CHAPTER 01 : VOLUMETRIC ANALYSIS

Volumetric analysis is the technique of finding the concentration of the solution. In this technique the solution of the known concentration is added repeatedly the one whose concentration is to be determined until there is just enough of it to neutralise the other of the unknown concentration. The method is called titration. During titration, the volume of standard solution that completely reacts with the measured volume of the solution under the analysis is recorded. The titration is repeated to obtain consistent titres. From consistent titre values, an average of volume of the standard solution is calculated. By us appropriate stoichiometry (reaction ratio) obtained from the balanced equation between the reacting substances in the experiment, the concentration of the solution under analysis can be calculated.

Volumetric analysis is performed using the following important laboratory apparatus. These include burette, pipette, conical flask, beakers, retort stand and clamp, volumetric flasks, weighing balance.

1.1. DETAILS OF APPARATUS USED DURING

TITRATION

a) Burette.

The burette is designed to deliver variable volumes of liquids. It is graduated from 0 to 50cm³ in units of 0.10cm³. Before use, the burette is rinsed with water, then a little of solution to be put in it. It is then clamped vertically and filled carefully with solution beyond the zero mark. The meniscus of the solution is then adjusted by draining it by opening the tap. Read the lower meniscus to get the accurate volume of the solution.

b)Pipette.

A pipette is designed to deliver a fixed or definite volume of a liquid such a 50, 25, 10, 5cm³. Before use, rinse the pipette with water followed by a little of the solution. The pipette is then filled by sucking the solution into it beyond the calibration mark. Close the mouth using the first finger, then adjust the meniscus to the mark by allowing the solution to flow down slowly. Then allow the accurately measured volume of the solution to flow into the conical flask under gravity. Do not blow; touch the side of the conical flask to allow the last drops to flow into the conical flask.

c) Conical flask.

The conical flask is where the pipetted solution is put; the flask must be cleaned with water. To the solution in the conical flask is added appropriate number of drops of indicator solution given. Mainly 2-3 drops are added. The indicator solutions include methyl orange, phenolphthalein indicator, bromocresol blue, bromocresol green, starch indicator, etc.

d) Beaker.

A beaker is designed to measure the varying volumes of solutions. It should be cleaned with water before use.

e)Retort stand and clamp.

These two are used together to clamp the burette as shown below.

1.2. SOLUTIONS

v Standard solution.

A standard solution is one whose concentration is accurately known.

The term concentration refers to the amount of solute dissolved in a specific volume of a solvent. One way of expressing the concentration of a solution is to state the number of moles of solute dissolved in 1000cm³ or 1litre of the solution. When one mole of a solute is dissolved in solvent (water) to make 1000cm³ of the solution, the solution is said to be a molar solution written as 1M or 1mol dm^-3. This is sometimes refered to as molarity.

A solution containing 5 moles of the solute in 1000cm³ or 1dm³ has a concentration of 5mol dm^-3 simply written as 5M. Similarly a solution containing 0.3 moles of sulphuric acid in 1000cm³ has a concentration of 0.3M, written as 0.3M sulphuric acid.

Qn. What would be the concentration/molarity of a solution containing 5moles in 2500cm³ of solution?

................................................................................................................................................................ ................................................................................................................................................................

a. Concentration in grams per litre or grams per cubic decimetres

The concentration can also be expressed in grams per litre or grams per cubic decimetres written as gl^-1 of gdm^-3 respectively. When 4g of sodium carbonate are dissolved to make 1 litre of solution, we say that the solution has a concentration of 4gl^-1 or 4gdm^-3 of sodium carbonate.

Example

53.5g of sodium chloride were dissolved to make 2000cm³ of the solution, calculate the

concentration of sodium chloride in grams per litre. (Na = 23, Cl = 35.5)

Solution

1000cm³ is the standard volume equivalent to 1dm³ or 1litre

1cm³ will be equal to 1 will be equal to

2000cm³ will be equal to 2000 X

2dm³ of solution contains 53.5g of NaCl

1dm³ of solution will contain g of NaCl

=26.75gdm^-3

Alternatively,

Since you know how to calculate the number of moles, we can first calculate the number of moles per litre/cubic decimetre and then convert to gdm^-3 as shown below.

R.F.M of NaCl = 23 + 35.5 = 58.5

Therefore molar mass of NaCl = 58.5g

This implies that 58.5g of NaCl contain 1 mole

1g of NaCl will contain moles

53.5g of NaCl will contain 53.5 X moles = 0.9145moles

2dm³ of solution contains 0.9145moles

1dm³ of solution will contain ^0.9145⁄₂ moles = 0.4573 moldm^-3 = 0.4573M

Therefore molarity = 0.4573M

1 mole of NaCl weighs 58.5g

Therefore 0.4573moles will weigh

b. Calculating the amount of substance in a given volume of solution

As stated before, the concentration of solution is quoted in terms of mol dm^-3 or gl^-1. The quoted figure is called molarity (M).

Given a solution of sodium hydroxide with molarity of 0.5M, it means that every 1000cm³ of that solution contains 0.5moles of sodium hydroxide. If there is uniform distribution of the solute (sodium hydroxide) in the solution and samples of different volumes of this solution are drawn from it.

Qn. How can we find the amount of sodium hydroxide in each of the drawn samples?

Let’s consider the example below,

If solution samples of volumes 5.00, 10.00, 25.00cm³ are drawn from a 0.5M solution of sodium hydroxide, calculate the number of moles of sodium hydroxide in each of the samples.

For 5.00cm³

0.5M means that 1000cm³of solution contains 0.5moles of sodium hydroxide

1.00cm³ of solution will contain moles

Therefore 5.00cm³ will contain X 5.00 moles

= 0.0025moles

For 10.00cm³

0.5M means that 1000cm³of solution contains 0.5moles of sodium hydroxide

1.00cm³ of solution will contain moles

Therefore 10.00cm³ will contain X 10.00 moles

= 0.005moles

For 25.00cm³

0.5M means that 1000cm³of solution contains 0.5moles of sodium hydroxide

1.00cm³ of solution will contain moles

Therefore 25.00cm³ will contain X 25.00 moles

= 0.0125moles

1.3. ACID-BASE TITRATION

Acid-base titration is the titration between an acid and an alkali. The reaction taking place is in this titration is called neutralisation reaction. The reaction is represented by the equation below,

H+(aq) + OH-(aq) strongO(l)

The progress of the reaction is determined by adding an indicator to the solution in the conical flask. At the end point, the indicator shows a sharp colour change. Students should take care when the end point is about to be reached. Add the solution from the burette drop by drop to avoid over shooting. At this level, the indicator solutions used for titration are phenolphthalein and methyl orange indicators. They show the following colours in acid and base media.

Indicator	Colour in acid medium	Colour in alkali medium
Phenolphthalein	Colourless	pink
Methyl orange	Red	yellow

A. TITRATION PROCEDURE

Given a solution for titration and a set of apparatus to be used,

a) Use a pipette to deliver appropriate volume of solution e.g 25.0, 20.0, 10.0, 5.0cm³ into a clean conical flask. The pipette must be rinsed water and the solution to be pipette.

b) Rinse the burette with some water followed by a little of the solution to be put in the burette. Fill the burette with the solution up to slightly beyond the zero mark and allow some of the solution to flow into the tip of the burette. Read the initial burette readings as V₁cm³

c) Arrange the apparatus as shown below, run the solution from the burette drop wise. Use your left hand to open the burette tap and your right hand to swirl the conical flask (unless you are left handed). Stop when the indicator just changes colour. This is the end-point of the solution.

d) Read the final burette reading as V₂cm³. Subtract the initial burette reading from final burette reading to obtain the volume of solution in the burette that completely reacts with a volume of standard solution in the flask, ie V = V₂ – V₁.

e) Repeat the titration several times to obtain consistent titres. Take closest titre values and determine their average. Use the average volume to calculate the concentration of the unknown using appropriate stoichiometry, or mole ratios. Reaction equation is crucial in obtaining reaction ratios of the reaction, B

B. FILLING THE TABLE

Volume of pipette = 25.0cm³

Experiment	1	2	3	4
Final burette reading (cm3)	25.40	27.00	44.90	36.80
Initial burette reading (cm3)	0.00	2.20	20.00	12.00
Volume of solution used (cm3)	25.40	24.80	24.90	24.80

Note the following,

vThe table must be filled to two decimal places with the last figure being a zero.

vThe subtraction must be correct

vTake values which a close to one another to calculate the average. This enhances precision; students should know that precision does not mean accuracy. Precision is simply the closeness of the measured values to one another whereas accuracy is the degree of agreement of the measured value to the accepted or accurate value.

vThe pipette volume must be indicated. Since the pipette is used to deliver a fixed volume. The volume is appropriately recorded to one decimal place; however there is no penalty for recording to two decimal places.

C. PRACTICAL SHEDULESa) Practical 1 Standardisation of sodium hydroxide with 0.1M hydrochloric acid

You are provided with the following

• 1 burette (50ml)

• 2 conical flask

• 1 pipette (20 or 25ml)

• Phenolphthalein indicator

• Solution of BA1 which is 0.1M hydrochloric acid solution

• Solution of BA2 which is sodium hydroxide solution

You are required to determine the concentration of solution of BA2 in

i. Mol dm^-3 or M

ii. gdm^-3 or gl^-1

Procedure:

Pipette 25.0 0r 20.0cm³ of BA2 into a clean conical flask. Add two drops of phenolphthalein indicator and swirl. Titrate the mixture with BA1 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below.

Volume of pipette used.................................................cm³

Experiment	1	2	3	4
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA1 used (cm3)

Values used to calculate the average volume of BA1

................................................................................................................................................................ ................................................................................................................................................................ ...............

Average volume of BA1

................................................................................................................................................................ .......................................................................................................... ...................................................... ................................................................................................................................................................

Calculate,

i. Number of moles of BA1 that reacted.

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

ii. The number of moles of BA2 that reacted.

................................................................................................................................................................ ................................................................................................................................................................ .............................................................................................................................

iii. The concentration of BA2 in mol dm^-3

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ..........................................................................................................................................................

iv. The concentration of BA2 that reacted in gl^-1

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

Teachers comment and evaluation

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ....................................................................................................

b) Practical 2 Standardisation of hydrochloric acid using sodium carbonate solution

You are provided with the following,

• BA3 which is approximately 0.2M hydrochloric acid

• BA4 which is made by dissolving 10.6g of sodium carbonate to make 1litre of solution  Methyl orange indicator

• 1 burette

• 1 pipette

• 2 conical flasks

• Stand and clamp

You are required to determine the concentration of BA3 in

i) Mol dm^-3 ii) gl^-1

Procedure,

Pipette 25.0cm³ of BA4 into a clean conical flask. Add 2 drops of methyl orange indicator into it and swirl. Titrate the mixture with BA3 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below,

Volume of the pipette used................................................cm³

Experiment	1	2	3	4
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA3 used (cm3)

Values used to calculate the average volume of BA3

.......................................................................................................................................................................

.............................................................................................................................................................

Average volume of BA3

....................................................................................................................................................................... .......................................................................................................................................................................

.......................................................................................................................................................

Calculate

i) number of moles of BA4 that reacted (Na = 23, C = 12, O = 16)

..................................................................................................................................................... ....................................................................................................................................................

ii) the number of moles of BA3 that reacted

..................................................................................................................................................... ..................................................................................................................................................... ..................................................................................................................................................... .....................................................................................................................................................

iii) the concentration of BA3 in mol dm^-3

..................................................................................................................................................... ..................................................................................................................................................... .....................................................................................................................................................

iv) the concentration of BA3 in gl^-1(H = 1, Cl = 35.5)

..................................................................................................................................................... .....................................................................................................................................................

.....................................................................................................................................................

Teacher’s comment and evaluation

....................................................................................................................................................................... ......................................................................................... .............................................................................. .............................................................................. ............................................................... .......................... ...............................................................................

c) practical 3 Determination of relative atomic mass of metal M in M₂CO₃

You are provided with the following solutions

• BA1 which is 0.2M hydrochloric acid solution

• BA2 which is a salt solution made by dissolving 10.6g 0f M₂CO₃ in 1litre of solution

You are required to determine the relative atomic mass of metal M in M₂CO₃

Procedure,

Pipette 25ml of BA2 into cleans a conical flask. Add two drops of methyl orange indicator to it and swirl. Titrate the mixture with BA1 from the burette. Repeat the titration to obtain consistent titres.

Record your results in the table below,

Volume..........................................................................cm³

Experiment	1	2	3	4
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA1 used (cm3)

Values used to calculate the average volume of BA1 ................................................................................................................................................................

............................................................................................................................

The average volume of BA1

................................................................................................................................................................ ......................................................... .......................................................................................................

..............................................................................................................

Calculate,

a)i) The number of moles of BA1 that reacted

................................................................................................................................................................ ....................................................................................... ......................................................................... .......................................................... ......................................................................................................

iii) write the equation of reaction between BA1 and BA2

................................................................ ................................................................................................

.................................................................. ............................................................

iv) write the mole ratio of the reaction

................................................................... .............................................................................................

..............................................................................................................................

b) The number of moles of BA2 that reacted

...................................................................... .......................................................................................... ........................................................................................ ........................................................................ .......................................................................................... ...................................................................... .......................................................................................... ......................................................................

c) Calculate the molarity of BA2

....................................................................... ......................................................................................... ............................................................................... ................................................................................. ........................................................................ ........................................................................................ ................................................................................. ............................................................................... ................................................................................................................................................................

d) Calculate the relative formula mass of M₂CO₃

...................................................................................................... .......................................................... ........................................................................................ ........................................................................ ...................................................................................................... .......................................................... ........................................................................................ ........................................................................

e) Determine the relative atomic mass of M( C = 12, O = 16)

....................................................................... ......................................................................................... ................................................................................... ............................................................................. ................................................................................................................................................................ ................................................................................................................................................................

Teachers comment and evaluation

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d) Practical 4 Determination of atomic mass of X in an acid

You are provided with the following,

BA3 which is a solution containing 1.7g of OH^- ions per litre

BA4 which is a dibasic acid H₂X containing 9.8gl^-1

You are required to determine the atomic mass of X in the acid (H = 1, O = 16)

Procedure,

Pipette 25 or 20ml of BA3 into a clean conical flask. Add 3 drops of phenolphthalein indicator. Titrate the mixture with BA4 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below,

Volume of pipette used...................................................................cm³

Experiment	1	2	3	4
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA4 used(cm3)

Values used to calculate the average volume of BA4

....................................................................... ......................................................................................... ............................................. ...................................................................

Average volume of BA4

................................................................................................................................................................ ................................................................................................................................................................ ........................................................................................

Write the ionic equation for the reaction between BA3 and BA4

................................................................................................................................................................

................................................................................................................

i)Calculate the molarity of BA3

............................................................................ .................................................................................... ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

i) Calculate the number of moles of BA3 that reacted

................................................................................................................................................................

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ .............................................................

ii) Calculate the number of moles of BA4 that reacted

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

................................................................................................................................................................ ................................................................................................................................................................

.............................................................

iii)Determine the molarity of BA4

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

.............................................................

iv)Calculate the relative atomic mass of X in the acid

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

.............................................................

Teachers comment and evaluation

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

....................................................................................................

e) Practical 5 Determination of the number of moles of water of crystallisation

You are provided with the following,

BA5 which is a solution containing 12.6g of dibasic acid Y.nH₂O per litre of solution

BA6 which is made by dissolving 8g of sodium hydroxide to make 1 litre of the solution (1 mole of Y reacts with 2 moles of sodium hydroxide, molar mass of Y = 90)

Procedure,

Pipette 25 or 20ml of BA5 into a clean conical flask. Add 3 drops of phenolphthalein indicator, then titrate with BA6 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below.

Volume of pipette used...................................................................cm³

Experiment	1	2	3	4
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA6 used(cm3)

Values used to calculate the average volume of BA6

................................................................................................................................................................

......................................................................................

Average volume of BA6

................................................................................................................................................................ ................................................................................................................................................................

.................................................

a)Calculate,

i)Molarity of sodium hydroxide.

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ............................................................. ii) The number of moles of sodium hydroxide that reacted. ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ .............................................................

iii)The number of moles of Y.nH₂O that reacted

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

................................................................................................................................................................ ................................................................................................................................................................

.............................................................

iv)The molarity of Y.nH₂O

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ .............................................................

v) Determine the value of n in Y.nH₂O

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

................................................................................................................................................................ ................................................................................................................................................................

.............................................................

Teachers comment and evaluation

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

....................................................................................................

f) Practical 6 Determination of the stoichiometry of the reaction between the acid H_nA and

sodium hydroxide

You are provided with the following

• BA1 which is 0.3M sodium hydroxide solution

• Ba2 which is 0.2M solution of acid HnA

Procedure,

Pipette 25 or 20ml of BA1 into a clean conical flask. Add 2 drops of methyl orange indicator.

Titrate the mixture with BA2 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below,

Volume of pipette used...................................................................cm³

Experiment	1	2	3	4
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA2 used(cm3)

Values used to calculate the average volume of BA2

................................................................................................................................................................

............................................................................................................................

Average volume of BA2

................................................................................................................................................................ ................................................................................................................................................................

............................................................................................................. a) Calculate the,

i)Number of moles of sodium hydroxide that reacted.

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ .......................................................... ii) The number of moles of H_nAthat reacted.

................................................................................................................................................................

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

..........................................................

b) Determine the mole ratio of the acid H_nA to sodium hydroxide.

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

................................................................................................................................................................ ................................................................................................................................................................

.............................................................

c) The value of n in H_nA

................................................................................................................................................................

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

.............................................................

Write the equation for the reaction.

................................................................................................................................................................

................................................................................................................

Teachers comment and evaluation

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

....................................................................................................

g) Practical 7 Determining the basicity of an acid H_nX

You are provided with the following

• BA1 which is 0.2 moles per litre of H_nX

• BA2 which is 0.5M solution of sodium hydroxide.

You are required to determine the basicity, n of the acid

Procedure,

Pipette 25 or 20ml of BA2 into a clean conical flask. Add 3 drops of methyl orange indicator.

Titrate the mixture with BA1 from the burette. Repeat the procedure to obtain consistent titres. Record the results in the table below,

Volume of pipette used...................................................................cm³

Experiment	1	2	3	4
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA1 used(cm3)

Values used to calculate the average volume of BA1 ................................................................................................................................................................

.............................................................................................................

Average volume of BA1

................................................................................................................................................................ ................................................................................................................................................................

........................................................................................

a)Calculate the,

I. Number of moles of sodium hydroxide that reacted

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ .............................................................

II. The number of moles of H_nX that reacted

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ .............................................................

III. Determine the mole ratio of the acid H_nX to sodium hydroxide

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

.............................................................

IV. The basicity, n of the acid H_nX

................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................

................................................................................................................................................................ ................................................................................................................................................................

.............................................................

Write an ionic equation of the reaction between the acid and base (sodium hydroxide)

................................................................................................................................................................

..........................................................................

Teachers comment and evaluation

................................................................................................................................................................ ................................................................................................................................................................

................................................................................................................................................................

....................................................................................................

h) Practical 8

You are provided with the following:

BA1 which is a solution containing 12.6gl^- of a dibasic acid of formula H₂C₂O₄.xH₂O. BA2 which is a 0.1M sodium hydroxide solution. You are required to determine the value of x

Procedure:

Pipette 20cm³ ( or 25cm³) of BA2 into a clean conical flask and add 2-3 drops of methyl orange indicator. Titrate this mixture with BA1 from the burette until the colour changes from yellow to orange. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used . . . . . . . . . . . . . . . . . . ...cm³

Experiment	1	2	3
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA1 used (cm3)

Volumes of BA1 used for calculating the average . . . . . . . . . . . . .cm³

Average volume of BA1 used . . . . . . . . . . . . . . . . . . ... cm³

Questions:

(a)Calculate the:-

(i) number of moles of BA2 reacted.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) number of moles of BA1 that reacted with BA2.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . .............

(iii) The concentration in moll^- of BA1 .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(iv) The R.M.M of the acid and hence the value of x.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

i) practical 9

BA1 which is a solution of acid H_nX of concentration 0.625M.

BA2 which is a 0.5M sodium hydroxide.

You are required to determine the reaction ratio for BA1 and BA2

Procedure:

Pipette 20cm³ (or 25cm³) of sodium hydroxide solution into a clean conical flask and add 2-3 drops of phenolphthalein indicator. Titrate this mixture with BA1 from the burette until the pink colour changes to colourless. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used . . . . . . . . . . . . . . . . . . ...cm³

Experiment	1	2	3
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA1 used (cm3)

Volumes of BA1 used for calculating the average . . . . . . . . . . . . .cm³

Average volume of BA1 used . . . . . . . . . . . . . . . . . . . . ... cm³

Questions:

(a)Calculate the:-

(i) Number of moles of BA1 reacted.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Number of moles of BA2 reacted.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(iii) The value of n (basicity of H_nX).

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(iv) The mole ratio.

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j) practical 10

You are to determine the value of R in RH₂ BA1 is an acid of formula RH₂ and was prepared by dissolving 1.125g of RH₂ in 250cm³ of distilled water.

BA2 is a n aqueous solution of sodium carbonate prepared by dissolving 2.65g of it in 250cm³ of distilled water.

Procedure:

Pipette 20 or 25 cm³ of BA1 into a conical flask add 1 – 2 drops of phenolphthalein indicator and titrate into it BA2 from a burette. Repeat the experiment until consistent results are obtained.

Results:

Capacity of pipette used . . . . . . . . . ..cm³

Experiment Number	1	2	3
Final burette readings cm3
Initial burette reading cm3
Volume of BA2 used cm3

Best 2 titre values to use to determine average volume of BA2

used . . . . . . . . . . . . . . . . . . . . . . . . . ..

Average volume of BA2

used . . . . . . . . . . . . . . . . . . . . . . . . ...

Questions:

(a) Calculate the

(i) Molarity of BA2

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. . . . .

(ii) Number of moles of BA2 that reacted

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(iii) Molarity of BA1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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(iv) Relative formula mass of RH₂

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(v) Value of R in RH₂

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k) practical 11

You are provided with the following:

BA1 which is a solution of an impure acid H₂X of concentration 2gdm^-3. BA2 which is a solution of sodium hydrogen carbonate made by dissolving 4.2g in 1dm^-3.You are required to determine the percentage purity of BA1

Procedure:

Pipette 20cm³(or 25cm³) of BA2 into a clean conical flask and add 2-3 drops of methyl orange indicator. Titrate this mixture with BA1 from the burette until the colour changes from yellow to pale pink colourless. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used . . . . . . . . . . . . . . . ...cm³

Experiment	1	2	3
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA1 used (cm3)

Volumes of BA1 used for calculating the average . . . . . . . . . . . . .cm³

Average volume of BA1 used . . . . . . . . . . . . . . . . . . . ... . cm³

Questions:

(a)Calculate the:-

(i) Number of moles of BA2 reacted.

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(ii) Number of moles of BA1reacted.

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(iii) Molarity of BA1.

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(iv) The percentage impurity of BA1 ( X = 88g)

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l) practical 12

You are provided with the following:

BA3 which is a 0.04M hydrochloric acid solution.

BA4 which is a solution made by dissolving 3.6g of Na₂CO₃.10H₂O to make 250cm³ of a solution.

You are required to determine the percentage impurity of BA4

Procedure:

Pipette 20cm³ (or 25cm³) of BA4into a clean conical flask and add 2-3 drops of methyl orange indicator. Titrate this mixture with BA3 from the burette until the colour changes from yellow to orange. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used . . . . . . . . . . . . . . . ...cm³

Experiment	1	2	3
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA3 used (cm3)

Volumes of BA3 used for calculating the average . . . . . . . . . . . . . .cm³

Average volume of BA3 used . . . . . . . . . . . . . . . . . . . . ... cm³

Questions:

(a) Write an equation for the reaction.

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(b) Calculate:-

(i) Moles of BA3 that reacted.

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(ii) The moles of Na₂CO₃.10H₂O in 250cm³ of a solution.

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(Iii) The percentage purity of Na₂CO₃.10H₂O.

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. . . . . . . . . . . . . . . . . . . . . . ( Na = 23, C = 12, O = 16, H = 1)

m) practical 13 You are provided with the following:

BA3 which is a 0.2M solution of a monobasic acid.

BA4 which is a solution made by dissolving 11.6g of Na₂CO₃.nH₂O to make a litre of a solution. You are required to determine the value of n

Procedure:

Pipette 20cm³ (or 25cm³) of BA4 into a clean conical flask and add 2-3 drops of methyl orange indicator. Titrate this mixture with BA3 from the burette until the end point. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used . . . . . . . . . . . . . . . . ...cm³

Experiment	1	2	3
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA3 used (cm3)

Volumes of BA3 used for calculating the average . . . . . . . . . . . . .cm³

Average volume of BA3 used . . . . . . . . . . . . . . . . . . . ... cm³

Questions:

(a)Calculate:-

(i) Moles of BA3 that reacted.

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(ii) Moles of Na₂CO₃.10H₂O in 1000cm³ of a solution.

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(Iii) The formula mass of BA4 and hence the value of n.

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Na = 23, C = 12, O = 16, H = 1)

n) practical 13

You are provided with the following:

BA1 which is a solution containing 6.2g of Y.nH₂O in one litre ( Y = 106, 1 mole of Y reacts with

2 moles of hydrochloric acid).

BA2 which is a 0.1M hydrochloric acid.

You are required to determine the number of moles of water of crystallization in BA1

Procedure:

Pipette 20cm³ ( or 25cm³) of BA1 solution into a clean conical flask and add 2-3 drops of phenolphthalein indicator. Titrate this mixture with BA2 from the burette until the pink colour changes to colourless. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used . . . . . . . . . . . . ...cm³

Experiment	1	2	3
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA2 used (cm3)

Volumes of BA2 used for calculating the average . . . . . . . . . . . . . .cm³

Average volume of BA2 used . . . . . . . . . . . . . . . . . . . . ... cm³

Questions:

(a)Calculate the:-

(i) Number of moles of BA2 reacted.

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(ii) Number of moles of BA1 reacted that reacted with the acid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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(iii) Concentration of BA1 in moles per litre.

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(iv) The value of n in Y.nH₂O.

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o) practical 14

You are provided with the following:

BA1, which is a solution containing 12.5gl^- of a mixture of anhydrous sodium carbonate and sodium chloride.

BA2, which is a 0.1M hydrochloric acid solution.

You are required to determine the composition of sodium chloride in BA1

Procedure:

Pipette 20cm³ (or 25cm³) of BA1 into a clean conical flask and add 2-3 drops of methyl orange indicator. Titrate this mixture with BA2 from the burette until the colour changes from yellow to orange. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results: Volume of pipette used . . . . . . . . . . . . . . . . ...cm³

Experiment	1	2	3
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of BA2 used (cm3)

Volumes of BA2 used for calculating the average . . . . . . . . . . . . .cm³

Average volume of BA2 used . . . . . . . . . . . . . . . . . . . ... cm³

(a)Calculate the:-

(i) Number of moles of BA2 reacted.

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(ii) Number of moles of BA1 that reacted with BA2.

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(iii) The concentration in moles per litre of BA1.

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

(iv) The percentage of sodium chloride in BA1.

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D. WORKED EXAMPLES

WORKED EXAMPLE 1

You are provided with the following:

BA1 which is a solution of 0.1M calcium hydroxide.BA2 which is sulphuric acid. You are required to determine the concentration of BA2

Procedure:

Pipette 20cm³ (or 25cm³) of BA1 into a clean conical flask and add 2-3 drops of phenolphthalein indicator. Titrate this mixture with BA2 until the pink color changes to colorless. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used: 20cm³

Experiment	1	2	3
Final burette reading (cm3)	8.30	16.30	24.40
Initial burette reading (cm3)	0.00	8.30	16.30
Volume of BA2 used (cm3)	8.30	8.00	8.10

NB: The table must be filled in two decimal places, accurately and not in pencil.

Volumes of BA2 used for calculating the average; 8.00cm³ and 8.10cm³

Average volume of BA2 used (8.00 + 8.10)/2 = 16.10 = 8.05cm³

Questions:

(a)Calculate the:-

(I) number of moles of calcium hydroxide in BA1 that reacted.

1000cm³ of solution contained 0.1 moles of calcium hydroxide

(20.0cm³ )/1000 of solution contained 0.1 x 20.0 moles of calcium hydroxide

= 0.002moles of calcium hydroxide

(ii) Number of moles of BA2 reacted.

Ca(OH)2 (aq) + strongSO4 (aq) CaSO4 (aq) + 2strongO (l) From the equation;

1 mole of calcium hydroxide reacted with 1 mole of sulphuric acid.

0.002moles of calcium hydroxide reacted with 1/1X 0.002 moles of sulphuric acid.

= 0.002moles

(iii) Concentration of BA2 in moles per litre.

8.05cm³ of solution contained 0.002 moles of sulphuric acid.

1000cm³ of solution contained ( 0.002 x 1000 )/8.05moles of sulphuric acid.

= 0.25 moles per litre.

NB: moles per litre is the same as M, moles per 1000cm³, and moles per 1dm³

(iv) Concentration of BA2 in grams per litre. (S = 32, O = 16, H = 1)

RFM of H₂SO₄ = (1X2 )+ (32X1) + (16X4) = 98

1 mole of HCl weighs 98g

0.25 moles of HCl weigh (98x 0.25)g

=24.5 g/l

NB: Using a formula anywhere leads to loss of marks.

WORKED EXAMPLE 2

You are provided with the following:

BA1, which is a solution made by dissolving 4.8g of metal hydroxide MOH in one litre.

BA2, which is a 0.0625 moll^- sulphuric acid.

You are required to determine the relative atomic mass of M in MOH

Procedure:

Pipette 20cm³ (or 25cm³) of BA1 into a clean conical flask and add 2-3 drops of phenolphthalein indicator. Titrate this mixture with BA2 until the pink color changes to colorless. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used; 25.0cm³

Experiment	1	2	3	4
Final burette reading (cm3)	24.10	48.10	24.00	48.10
Initial burette reading (cm3)	0.00	24.10	0.00	24.00
Volume of BA2 used (cm3)	24.10	24.00	24.00	24.10

Volumes of BA2 used for calculating the average. 24.00cm3 and 24.00cm3

Average volume of BA2 used 24.00 + 24.00 = 48.00 = 24.00cm³

2 2

Questions:

(a) Calculate the:-

(i) Number of moles of BA2 reacted.

1000cm³ of solution contained 0.0625 moles of sulphuric acid

(24.00cm³ ) of solution contained (0.0625 x 24.00)/1000 moles of sulphuric acid

= 0.0015moles of sulphuric acid

(ii) number of moles of MOH in BA1 reacted.

2MOH (aq) + strongSO4 (aq) M2SO4 (aq) + 2strongO (l)

From the equation;

1 mole of sulphuric acid reacted with 2 mole of MOH

0.0015mole of sulphuric acid reacted with (2x 0.0015) mole of MOH

= 0.003 mole of MOH

(iii) molarity of BA1 .

25.0cm³ of solution contained 0.003 moles of hydrochloric acid.

1000cm³ of solution contained (0.003 x 1000)/25.0 moles of hydrochloric acid.

= 0.12M

(iv) The formula mass of MOH.

0.12moles of MOH were contained in 4.8g

1 moles of MOH was contained in (4.8/0.12)g

= 40g

(V) The R.A.M of M (O = 16, H = 1)

Relative formula mass of MOH = (mx1) + (16x1) + (1x1) = 40 Then; m+17 = 40 M = 23.

WORKED EXAMPLE 3

You are provided with the following;

GA1, which was a solution made by dissolving 12.6g of a monobasic acid HNO_X to make 1 litre of solution.

GA2, which is a 0.2M sodium hydroxide solution.

You are required to determine the value of X in HNO_X

Procedure:

Pipette 25cm³ (or 20cm³) of GA2 into a clean conical flask and add 2-3 drops of phenolphthalein indicator. Titrate this mixture with GA1 until the pink colour changes to colourless. Repeat the titrations two more times for consistent results and enter your results in the table below.

Results:

Volume of pipette used = 25.00cm³

Experiment	1	2	3	4
Final burette reading (cm3)	25.20	25.10	25.00	25.00
Initial burette reading (cm3)	0.00	0.00	0.00	0.00
Volume of GA2 used (cm3)	25.20	25.10	25.00	25.00

Volumes of GA2 used for calculating the average; 25.00cm³ and 25.00cm³

Average volume of GA2 used (25.00 + 25.00)/2 = 50.00 = 25.00cm³

Questions:

(a) Write an ionic equation for the reaction between the acid in GA1 and sodium hydroxide in GA2

H⁺ _(aq) + OH^- _(aq) H₂O _(l)

(b) Calculate;

(i) Moles of sodium hydroxide in GA2 that reacted with the acid

1000cm³ of solution contained 0.2moles of sodium hydroxide

25.00cm³ of solution contained (0.2 x 25.00)/1000 moles of sodium hydroxide

= 0.005moles of sodium hydroxide

(ii) Number of moles of HNO_X in GA1 reacted.

From the equation;

1 mole of sodium hydroxide reacted with 1 mole of MOH

0.0015mole of sodium hydroxide reacted with (1/1x 0.005) mole of MOH

=0.005 mole of MOH

(iii) Molarity of GA1.

25.0cm³ of solution contained 0.005 moles of hydrochloric acid.

1000cm³ of solution contained (0.005 x 1000 )/25.0 moles of hydrochloric acid.

= 0.2M

(iv) The formula mass of HNO_X

0.2moles of HNO_X were contained in 12.6g

1 moles of HNO_X was contained in (12.6/0.2)g

= 63g

(V) the value of X ( O = 16, H = 1, N=14)

Formolar mass of MOH = (1x1) + (14x1) + (Xx16) =40 Then; 16X+15 = 63 16X = 48.

X = 3

WORKED EXAMPLE 4

You are provided with the following

BA1, which is a solution containing 10g of solid Y.10H₂O per 500cm³ (Y = 202)

BA1, which is 0.1M hydrochloric acid solution

Ratio of Y: HCl is 1:2

You are required to determine the percentage purity of solid Y.10H₂O

Procedure:

Pipette 25 (or 20) cm³ of BA1 into a clean conical flask. Then add 2 – 3 drops of methyl orange indicator and titrate with solution BA2 until you obtain a persistent colour change. Repeat the titration 2 – 3 times to obtain consistent results. Enter your results in the table below.

Results:

Volume of pipette used = 25cm³

Final burette reading/cm3	15.40	30.90	46.30
Initial burette reading/cm3	0.00	15.40	30.90
Volume of BA2 used/cm3	15.40	15.50	15.40

Titre values used for calculating average volume of BA2;

15.50cm³ and 15.40cm³

Average volume of BA2 = 15.45cm³

Questions:

(a) Calculate the

(i) Moles of hydrochloric acid in BA2 that reacted

1000cm³ of solution contained 0.1 moles of calcium hydroxide

15.45cm³ of solution contained (0.1 x 15.45)/1000 moles of calcium hydroxide

= 0.001545moles of calcium hydroxide

(ii) Moles of Y in BA1 that reacted with hydrochloric acid.

From the mole ratio;

2 moles of the acid reacted with 1 mole of Y

0.001545 moles of the acid reacted with (0.001545/2) moles of Y

= 0.000772 moles of Y

(iii) Molarity of BA1 and hence the percentage purity of the solid, Y.10H₂O (4 marks)

25.0cm³ of solution contained 0.000772 moles of hydrochloric acid.

1000cm³ of solution contained (0.000772 x 1000)/25.0 moles of hydrochloric acid.

= 0.03088M

RFM of Y.10H₂O = 202 + 180 = 382

1 mole of Y.10H₂O weighs 382g

0.03088 moles of Y.10H₂O weigh (382x 0.03088) g

= 11.7g/l

Also

500cm3 of BA1 contained 10g of Y.10H₂O

1000cm3 of BA1 contained (10 x 1000)500 g of Y.10H₂O

= 20g/l

Therefore, the percentage purity of Y.10strongO in BA1 = (11.7 x 100 %)/20

= 58.5%

NB: Percentage impurity = 100 – (percentage purity)