PRESENT’S OFFICE, REGIONAL ADMINISTRATION

AND LOCAL GOVERNMENT

SECONDARY EXAMINATION SERIES

CHEMISTRY FORM FOUR 

MID-TERM EXAMS – AUG/SEPT – 2024

TIME: 2:30 HRS

INSTRUCTIONS 

1.  Thus paper consists of section A, B and C with total of  eleven (11) questions
2.  Answer all questions
3.  All writing must be in blue or Black in except drawing which must be in pencil
4.  Section A and C carry fifteen (15) marks
5.  Cellular phones and any unauthorized material are not allowed in assessment room

 SECTION A

Answer all questions in this section

1.               For each of the items (i) - (x) choose the correct answer from the given alternatives and its letter in the answer sheet provided.

1. Zinc reacts with dilute acids displacing hydrogen, but copper does not. This indicates that; -

1.              Zinc is higher in the activity series than hydrogen and copper
2.               Zinc is less reactive than copper
3.              Copper is more electropositive than zinc
4.             Copper is inert
5.               Copper is found above zinc and hydrogen in the electrochemical series.

2. The reason that made scientists to stop using hydrogen gas in filling balloons is; -

1.              The gas became denser than air
2.               The gas is less dense than air
3.              Discovery of helium gas
4.             The gas is soluble in water
5.               The gas is highly flammable and burns with pop sound.

3. What fire extinguisher will you use to help your friend whose shirt caught fire during an experiment in the laboratory?

1.              Powder fire extinguisher
2.               Fire blanket
3.              Carbon dioxide
4.             Water
5.               Foam.

4. The nuclide notation of element Z is ₁₅³¹Z which set of sub-atomic particles is collect?

1.              15 protons, electrons 16, and 15 neutrons
2.               15 protons,15 electrons, and 16 neutrons
3.              15 protons, 15 electrons and 15 neutrons
4.             16 protons, 16 electrons and 15 neutrons
5.               16 protons, 15 electrons, and 15 neutrons

5. A form four student was given the following staffs for preparation of ammonia gas.

1.                  Source of heat
2.                 Calcium hydroxide
3.                  Ammonium chloride
4.                 Solid potassium hydroxide

6. A rapid chemical reaction that release energy in form of light and heat is called; -

1.              Neutralization
2.               Decomposition
3.              Combustion
4.             Precipitation
5.               Displacement

7. Which of the following pairs constitute the best methods for treating and purifying water?

1.              Chlorination and distillation
2.               Chlorination and sedimentation
3.              Disinfection and decantation
4.             Disinfection and filtration
5.               Chlorination and aeration

8. The equation below shows the dissociation of sulphuric acid into ions: -

H₂SO_4(aq)       H⁺ _(aq)  + SO4^2- _(aq). From the equation, how many ions are there in 9.8g of   H₂SO₄?

1.              2.9x10²³ ions
2.               1.22x 10²³ions
3.              8.9 x10²³ions
4.             1.81x10²³ions
5.               0.3x10²³ions

9. Why oxygen differs from other gases?

1.              It explodes and support combustion
2.               It neither burns nor support combustion
3.              It burns but does not support combustion
4.             It supports combustion but does not burn
5.               It burns and support combustion

10. In the following equilibrium equation

the forward reaction is exothermic. Which change would increase the production of Sulphur trioxide at equilibrium?

1.              Adding a catalyst
2.               Decreasing pressure
3.              Increasing temperature
4.             Decreasing Sulphur trioxide concentration
5.               Decreasing temperature

2.               Match the items in list A with the correct response in List B by writing the letter of the correct response in the box provided bellow

SECTION B (54 marks)

Answer all questions in this section

3.               (a) Form four students wanted to verify the presences of water in an unknown compound using hydrated copper (II) sulphate. A small amount of hydrated copper (II) sulphate was placed on watch glass followed by addition of few drops of the unknown compound. Then was no change in the colour observed.

1.                  Why was there was no change in the colour of hydrated copper (II) sulphate?
2.               What other substance that could be in the place of the hydrated copper (II) sulphate to observe the required colour change.

(b) What is so called the universal solvent comment on this statement

4. Chemistry teacher guided students of form four to study carefully an experiment carried out in order to distinguish various substances formed during an experiment. The procedures were as follows

1.                                    Measure about 120cm3 of water and pour it in a beaker
2.          Add a spatula full of common salts and stir to allow salts to dissolve
3.                                    Continue to add more salts to the solution, stirring until no more salts can dissolve
4.          Place the solution on tripod stand and heat gently as you continue stirring
5.                                    Stop heating when salts dissolves
6.                                     Place the beaker in a trough of cold water and allow cooling for 3 to minutes note the results observed
   1.                                                   What type of solution was obtained when a spatula full of table salt were dissolved in 120 cm3 of water at room temperature?   Give reasons
   2.          What type of solution was obtained when no more salts dissolved in cold water at room temperature? Give reason
   3.           What is the name of the final solution obtained after cooling through of coldwater? Give reason
   4.              Explain the two (2) application of the concept studied above

5. Mwasiti was supplied with two beakers, one containing 0.1M KOH standard solution, and the other beaker containing sulphuric acid solution whose molarity was not known.  She was asked to find the molarity of the acidic solution. Mwasiti took the basic solution and put it into the burette, then she measured accurately 25cm³ of sulphuric acid using a measuring cylinder and transferred it into a conical flask, she is then added few drops of methyl orange indicator.

Her titration results were showing that 25cm³ of acid required 2cm³ of KOH standard solution.

She used the following formula to calculate the molarity of the sulphuric acid.

Molarity of H₂SO₄ acid = (Volume of acid   x   Volume of base)/Molarity of base

(a) What are the mistakes Mwasiti performed in her titration? (Four mistake).

(b) For each mistake, suggest the correct measure you would take.

6. (a) A person suffering from in digest ion produces1.0Litre of gastric juices per day which contains about 2.0g of hydrochloric acid. How many antacid tablets each containing 400mmg of sodium bicarbonate (NaHco3) is needed to neutralize all the hydrochloric acid produced in a day?

2.                                Name the suitable warning sign that you would find on the following: -

1. A bottle containing concentrated sulphur in a day?
2. A bag contain ingrator insect poison
3. Room door containing x–ray machine
4. Bag containing dynamites

7. Explain how the following factors affect the rate of chemical reaction

1.                                               Pressure (ii) Temperature

2.          Sodium hydroxide was dissolved in water after a while the container. Holding the solution was observed to be hat
   1.                                Basing on the heat change, name there action that took place in the above process
   2.         Suggest any two application of  there action above in our everyday
   3.       Draw energy level diagram for the above process named in b(i)

8. During electrolysis of an aqueous of salt of metal X, a current of 2.0A was passed for 26 minutes and 32 seconds. The mass of metal ‘X’ deposited was 0.24g.

1. On which electrode was the metal X deposited?
2. Calculate the amount of charge needed to deposit 1 mole of metal X.
3. Calculate the charge carried on the ion.
4. Write an ionic equation to show how the ions of the metal X are discharged at the electrode (R.A.M. of metal X= 24)

SECTIONC (30 MARKS)

Answeronlytwo(02) questionsfromthissection.

9. Agriculture is back bone of our economy but the addition of in organic fertilizers in the farm is not as important as addition of organic manure. Discuss the correctness of this statement in four points.

10. The extraction of metals has economic advantageous in Tanzania, but it’s still destructive to the environment. Illustrate three (3) environmental destructions may be caused by the process, and suggest three (3) control measure to problem.

11. (a)Name the process used to obtain an aqueous solution of ethanol from a sugar, for example Glucose (C₆H₁₂O₆)

(b) States without further description, the method you would use to obtain a sample of reasonably pure ethanol from the aqueous solution, and indicate the physical properties to which this separation in based.

 (c) Briefly explain the following chemical reaction which takes place when: -

1. Ethanol burns in air with a pale blue flame.
2. Sodium is added to a pure ethanol; a colorless gas is evolved.

PRESENT’S OFFICE, REGIONAL ADMINISTRATION AND LOCAL GOVERNMENT

SECONDARY EXAMINATION SERIES

CHEMISTRY FORM FOUR

MID-TERM EXAMS – AUGUST – 2023

032/1 CHEMISTRY 1

TIME: 3:00 Hours YEAR. 2023

Instructions

1. This paper consists of sections A, B and C with a total of eleven (11) questions.
2. Answer all questions in section A and B and any two (2) question from section C
3. Section A carries sixteen (16) marks, section B carries fifty four (54) marks and section C carries thirty (30) marks.
4. All writing must be in blue or black ink except drawings which must be in pencil
5. All communication devices and any unauthorized materials are not allowed in the examination room
6. Write your Examination Number on every page of your answer sheet(s) provided.
7. The following constants may be used;

• Atomic masses H=1, C=12, K=39, O=16,S=32, Cl=35.5
• Avogadro’s constant = 6.02x10²³
• GMV at S.T.P = 22.4dm³
• 1Faraday =96500C
• 1Litre=1dm³=1000cm³

SECTION A: (16 Marks)

Answer all questions

1. For each of the following items (i) – (x) choose the correct answer among the given alternatives and write its letter besides the item number on the answer sheets provided.

1. A form one student saw the "flammable" sign on a box and made the following possible interpretations. Which one is the most correct?

1. The box contained firewood
2. The box contained papers
3. The box had radioactive materials
4. The box contained spirit used in lamps
5. The box contained health hazards

2. What should be done if the results obtained from an experiment do not support the hypothesis?

1. Experiment should be changed
2. Results should be left out
3. Ideas for further testing to find a solution should be given
4. Problem should be identified
5. Hypothesis should be accepted

3. The reaction between potassium metal and water is

Which of the following statement is true about this reaction?

1. Hydrogen is oxidized
2. potassium is reduced
3. Potassium is the reducing agent
4. Hydrogen is the reducing agent
5. Water is both oxidizing and reducing agent

4. How many molecules are there in 16.8litres of chlorine gas at STP?

1. 4.517 X10²³
2. 7.5 X10²³
3. 8.029 X10²³
4. 9.033X10²³
5. 6.75 X10²³

5. Ammonia is the basic gas that can obtained by reacting ammonium salt and calcium hydroxide. Which of the following can be used to dry ammonia during its preparation.

1. Concentrated sulphuric acid.
2. Calcium Chloride
3. Lime water
4. Calcium oxide.
5. Calcium Carbonate

6. Mr John treated water for domestic purpose, unfortunately the water remained hard on boiling and formed no leather with soap. Suggest the ions present in the water.

1. Ca²⁺ and HCO₃^-.
2. Ca²⁺ and CO₃ ^2-
3. Mg²⁺ and SO₃^2-
4. Mg²⁺ and HCO₃^-.
5. Mg²⁺ and SO₄^2-.

7. A mixture of 100cm3 of ethanol and 100cm3 of pure water can be separated by....

1. Solvent extraction
2. Simple distillation
3. Evaporation
4. Fractional distillation
5. Filtration

8. If Mr. Kashamba wants to electroplate his spoon with copper sulfate solution, he should arrange the electrode in the following way...

1. Spoon as Anode and copper cathode.
2. Spoon cathode and copper Anode
3. Spoon Anode and carbon cathode.
4. Spoon cathode and copper(II) sulphate anode
5. Carbon cathode and copper Anode

9. Which of the following sets represents isotopes of an element?

1. ¹⁶₇K , ⁷₈K and ¹⁸₉K
2. ¹⁶₇K , ¹⁶₉K and ¹⁶₈K
3.  and
4. ¹⁶₈K , ¹⁷₈K and ¹⁸₉K
5. ¹⁶₉K , ¹⁶₈K and ¹⁷₈K

10. Asha harvest unripe mangoes from her fruit garden, she then keep them till ripe and sell the mangoes. What changes occur for mangoes to turn ripe from unripe?

1. Physical change.
2. Chemical change.
3. Physical and chemical change
4. Neither physical nor chemical change.
5. Physical change and taste change

2. Match the uses of apparatus in list A with the respective element in list B by writing the letter of the correct response besides the item number in the answer sheet provided

SECTION B (54 Marks)

Answer all questions in this section

4, Juma was given two gas jars, one containing gas “X” and another one containing gas “Z” Gas “X” is used to prepare water gas in the laboratory and gas “Z” is used treating sewage plants

1. Identify the two gases
2. With reasons give the method used to collect gas “Z” in the laboratory
3. Give three uses of gas “X” in our daily life

4. 16.8 g of impure potassium hydroxide was dissolved in distilled water to make 100 ml. 20mls of this solution required 28mls of 0.07M sulphuric acid to react. Calculate;

1. Molarity of KOH
2. Mass concentration of pure KOH

5. (a) A form three student performed two different experiments

Experiment I; Students dissolved one tea spoon of sugar in cold water

Experiment II: Students dissolved one tea spoon of sugar in hot water

By using the concept of collision theory explain in which experiment the sugar dissolved more quickly?

(b)You are provided with the following equilibrium reaction

What happens to the production of ammonia if

1. Pressure increased
2. The equilibrium system is cooled
3. Hydrogen is removed
4. Nitrogen increased

6. Samwel bought all necessary building materials as he wanted to build modern and expensive house for his mother, four months later he found that almost all nails and iron sheets have been rusted, unfortunately he has no any extra money to buy the new nails and iron sheets. As a chemist student what will you advise Samwel (Give two points)

(b) Suppose you are in a bus travelling for annual holiday, a bus driver went to the petrol station to fill fuel but he forget to switch off the bus engine, this caused explosion hence the fire started.

As a form four student

1. How will you be able to use fire extinguisher to fight against fire?
2. Which type of fire extinguisher will be suitable for you to use? Give reason of your choice

7. (a)What are the four stages for extraction of moderate reactive metals

(b) In certain areas iron can be extracted through blast furnace which involve different temperatures such as1000⁰C, 750⁰C and 250⁰C in different stages

1. What is the chief ore in the extraction of iron
2. At what temperature reduction taking place?
3. What are the importance of coke, hot air and waste gases

(c).What are the two environmental effects caused by extraction of metals

8. During manufacturing of Sulphuric acid, Sulphur trioxide gas is dissolved in concentrated sulphuric acid instead of dissolving it directly in water

1. Explain why? And Write a balanced equation of dissolution of the gas in the acid
2. Write a balanced chemical equation for each of the following

1. Sulphuric acid act as an acid
2. Sulphuric acid act as an oxidizing agent.

SECTION C (30 Marks)

Answer only two questions from this section

9. Explain the term substitution reaction as applied in organic chemistry

(b)With the use of chemical tests differentiate between saturated hydrocarbons and unsaturated hydrocarbons.

(c). Write and name all isomers of pentane

10. The head master of Mtakuja secondary school advised an environmental master to use manure and fertilizers in order to improve the growth of trees and plant around the school .What are the significance of manure and fertilizers as per head masters advise.(Five points)

11. There are various environmental plans to be used in controlling the solid waste and soil pollution in Mbozi municipality. Advise accordingly to the effective plans to be taken in order to achieve such activities.( Five points)

THE PRESIDENT’S OFFICE MINISTRY OF EDUCATION, REGIONAL ADMINISTRATION AND LOCAL GOVERNMENT

COMPETENCY BASED SECONDARY EXAMINATION SERIES

CHEMISTRY

FORM FOUR- SEPT 2022

CODE 032/1

INSTRUCTIONS

1. This paper consists of sections A, B and C with a total of fourteen (14) questions
2. Answer all questions in sections A and B and one (1) question from section C
3. Sections A and C carry fifteen (15 ) marks each and section B carries seventy (70) marks
4. Cellular phones and any unauthorized materials are not allowed in the examination room
5. Write your Examination Number on every page of your answer booklet(s)
6. The following constants may be used

Atomic masses H=1, C=12 , N=14, O=16 , Cl=35.5 , CU=64 , P=15, Fe=56

Avogadro’s number =6.02 x 1023.

GMV at s.t.p= 22.4 dm3.

1 Faraday = 96,500 coulombs.

Standard pressure =760 mm Hg.

Standard temperature =273 K.

1 litre = 1 dm3 =1000 cm3.

SECTION A (15 Marks)

Answer all questions in this section

1. For each of the items (i) - (x), choose the correct answer from among the given alternatives and write its letter beside the item number in the answer booklet provided.

1. A metal nitrate which will not give a metal oxide on heating is:

1. Calcium nitrate 
2. Silver nitrate 
3. Lead nitrate
4. Copper nitrate
5. Zinc nitrate

2. What number of faradays of electricity is required to deposit 4g of calcium from molten calcium chloride?

1. 0.1 
2. 0.2 
3. 0.4 
4. 0.3 
5. 0.7

3. When methane undergoes substitution reaction with excess chlorine. What is the final product?

1. Chloromethane
2. Dichloromethane
3. Trichloromethane
4. Tetracloromethane
5. Monochloromethane

4. The reason why white anhydrous copper (II) Sulphate turns blue when exposed in Atmosphere is that it

1. Absorbs water vapour
2. Reacts with oxygen
3. Reacts with carbon dioxide
4. Become dry
5. Release water to the Atmosphere

5. Which action should be taken immediately after concentrated sulphuric acid is spilled on the skin?

1. It should be rinsed off with large quantities of running water.
2. It should be neutralized with concentrated NaOH
3. The affected area should be wrapped tightly and shown to a medical health provider
4. It should be Neutralize with solid CaCO₃
5. It should be neutralized with concentrated KOH

6. The molarity of 5.3g in 100ml of Na₂CO₃ solution is

1. 0.2M
2. 0.5M
3. 0.05M
4. 0.005M
5. 0.01M

7.                     The reaction between hydrogen and Iodine is represented by H_2(g) + I_2(g) 2HI_(g) H=-xKJ/mol The reaction is

1. Endothermic reaction
2. Neutralization reaction
3. Displacement reaction
4. Exothermic reaction
5. Decomposition reaction

8.                   One of the following apparatus is used to measure fixed volume of liquid

1. Burette
2. Pipette
3. Conical flask
4. Measuring cylinder
5. Volumetric flask

9. A substance which absorb water from the atmosphere and form a solution is called

1. Efflorescent 
2. hygroscopic 
3. deliquescent
4. amphoteric
5. salt

10. AgNO_3(aq) + NaCl_(aq) → AgCl_(s) + NaNo_3(aq). This a good example of

1. Neutralization reaction 
2. double decomposion reaction 
3. Redox reaction 
4. synthesis reaction
5. decomposition.

2. Match the properties of element in list A with the respective element in List B by writing the letter of the correct response besides the item number in answer sheet provided.

3. (a) The Modem periodic law is based on modification of Mendeleev periodic law. Explain how the two theories differ from each other.

(b) Comment on the following statement

(i) Lithium has large size than Beryllium

(ii) Sodium is smaller than potassium

(c) Give any four ions whose electronic configuration resemble to that of Neon. (07 Marks)

4. a) How many chlorine molecules are in 20cm³ of chlorine gas at s.t.p.

b) Calculate number of ions present in 5g of copper (II) Nitrate

5. (a) (i) People suffering from heart burn usually use wood ashes for relief. Mention chacteritics which makes the ashes to be used for heart burn relief.

(ii) Give four compounds found in the laboratory which show the same characteristic as ashes. 

(b) How many ions are there in 6.82g of Al₂(SO₄)₃

6. 5.3g of X₂CO₃ was dissolved in water to make 0.5 litre of a solution. 25cm³ 0f this solution required 50.0cm³ of 0.1M HCl for complete neutralization.

a) Write the balanced chemical equation for the reaction

b) Calculate the concentration of X₂CO₃ in mol/dm³

c) Calculate the relative molecular mass of X₂CO₃

d) Calculate the relative atomic mass of X

e) What is the name and symbol of element X

7. (a) A gaseous compound consists of 86% Carbon and 14% Hydrogen by mass. At S.T.P, 3.2dm³ of the compound had mass of 6g.

(i) Calculate its molecular formula

(ii)Give the IUPAC name of the compound

(b) Most of the apparatus in the laboratory are made up of glass materials. Support this statement by giving ant two (2) reasons. (07 Marks)

8. Element R having atomic number 20 combines with element S having atomic number 17 to form a certain compound

a) Write the formula of the compound and state the type of bond formed in the compound

b) Give any three properties of the compound formed in 7(a) above

9. a) Muumini is a student from Katosani secondary school, she is not able to State Le Chatellier’s principle, Help her.

b) In the industrial preparation of Sulphur trioxide mr Atieno yo established equilibrium between Sulphur dioxide and oxygen gas as follows:

2SO_2(g) + O_2(g)   2SO_3(g)∆H= - 94.9KJ/mol.

i. How would you adjust temperature and pressure to maximize the proportion of the product at equilibrium? 

ii. Why is it unfavorable to work with very high pressure and very low temperature in the contact process? 

iii. What catalyst is used to speed up the rate of formation of Sulphur trioxide before attaining the equilibrium?

10. a) Mr Mapulishi tasked to prepare all requirements for extraction of sodium.Describe the use of each of the following during extraction of Sodium

i. Calcium Chloride ii. Graphite anode

iii. Steel gauze

b) .Why sodium is collected by upwards in the downs cell

c) Write electrodes reaction in downs cell during extraction of Sodium

11. Mr Kalubandika wanted to know some chemistry pertaining concepts. Help Mr Kalubandika to answer the following conceptual questions.

a) In which other areas do we find the warning signs out of laboratory (give four point)

b) Explain how measurements of volume differ when using measuring cylinder and burette

c) It is recommend that laboratory apparatus should be properly washed or wiped after use, explain the significance for this when

i. Measuring volume of liquids

ii. Measuring mass of substance

12. (a) Give the meaning of the following terms

(i) Soil pH (ii) Liming

(b) (i) Explain why sulphur and its compounds are removed from the fuel before they are burned

(ii) By using a reaction equation explain how propane differs from propene

13. (a) Outline any three uses of carbon dioxide gas in animals and plants

(b) Complete the following reactions

(i) CH₂=CH₂ + O₂

(ii) CaC₂ + 2H₂O 

(iii)CH₄ +Cl₂  

(iv) C₂H₅OH +O₂  

14. In q certain chemical plant that deals with the production of hydrogen gas, a certain chemist passes an electric current in series through copper (II) Sulphate and sulphuric acid solutions. In both electrolytes, inert electrodes were used. If 8400cm3 of hydrogen at S.T.P were produced for several hours, what volume of oxygen gas would also be produced? What mass of copper was produced?

THE PRESIDENT'S OFFICE

MINISTRY OF REGIONAL GOVERNMENT AND LOCAL GOVERNMENT

PRE-NATIONAL  EXAMINATION SERIES-1

CHEMISTRY  FORM-4

2020

TIME: 3:00 HRS

Instructions

1. This paper consists of sections A, B and C with a total of fourteen (14) questions.
2. Answer all questions in sections A and B and one (1) question from section C.
3. Cellular phones and any unauthorised materials are not allowed in the examination room.
4. Write your Examination Number on every page of your answer booklet(s).
5. The following constants may be used.

Atomic masses: H 1, O- 16, N- 14, S = 32, Zn - 65, Cl -35.5, cu - 64.

Avogadros number= 6.02 x 10²³

GMV at s.t.p =22.4 dm³ .

1 Faraday= 96,500 coulombs.

Standard pressure = 760 mm Hg. Standard temperature 273 K.

1 litre =1 dm³ =1000 cm 3.

SECTION A (15 Marks)

Answer all questions in this section.

1. For each of the items (i) — (x), choose the correct answer from among the given alternatives and write its letter beside the item number in the answer booklet provided.

(i) "Water is referred to as the universal solvent". What does this mean? 

1. Water is neither acidic nor basic as compared to other liquids.
2. Water exists in three states of matter than any other liquids.
3. Water dissolves both organic and inorganic solutes. 
4. Water is used more domestically than any other liquids.
5. Water dissolves more substances than any other known liquids.

 (ii) A current of 0.2 A was passed through an electrolyte for 16 minutes and 40 seconds. What is the quantity of electricity produced in coulombs?

1.  2000 C  
2. 1000 C 
3.  200 C 
4.  0.20 C 
5.  7686 C.

(iii) Substance X liberates chlorine gas from acidified potassium chloride. The behaviour of X is described as:

1.  an oxidising agent    
2.  an oxidising and reducing agent
3.  catalyst   
4.  a reducing agent
5.  bleaching agent.

(iv) Which carbonate is the most stable to heat?

1.  Calcium carbonate   
2.  Copper (II) carbonate
3.  Lead (II) carbonate 
4.  Zinc carbonate 
5. .Iron (II) carbonate.

(v)  Aluminium does not react with water and does not corrode much in air because

1.  it is below hydrogen in the reactivity series
2.  it forms a stable carbonate which prevents reactions
3.  the metal is covered with a protective coating of an oxide 
4.  aluminium ions have positive charges
5.  it is very stable.

(vi) Which of the following compounds does NOT belong to the alkenes homologous series?

1.  C₂H₄ 
2.  C₃H₆  
3.  C₄H ₈ 
4.  C₅H₁₀ 
5.  C₆H ₁₄.

(vii) Which of the following is NOT among the composition of air?

1. Noble gases 
2. Carbon dioxide 
3. Nitrogen 
4. Hydrogen 
5. Water vapour. 

(viii)   Chlorine ion, Cl^- differs from chlorine atom because it has       

1.   more protons. 
2.  less protons. 
3.  more electrons. 
4.  less electrons. 
5.  more neutrons.

(ix) Which of the following pairs of compounds can be used in the preparation of calcium sulphate?

1. Calcium carbonate and sodium sulphate
2. Calcium chloride and ammonium sulphate
3. Calcium hydroxide and barium sulphate 
4. Calcium nitrate and lead (II) sulphate 
5. Calcium chloride and barium sulphate. 

(x)  Which of the following solutions is the most concentrated?

1. 50 g of calcium carbonate in 100 cm³ of water
2. 60 g of sodium chloride in 200 cm³ of water
3. 65 g of potassium nitrate in 100 cm³ of water
4. 120 g of potassium sulphate in 200 cm³ of water
5. 50 g of sodium hydroxide in 200 cm³ of water.

2.  Match the items in List A which the responses in List B by writing the letter of the correct response beside the item number in the answer booklet provided.

SECTION B (70 Marks)

Answer all questions in this section.

3. (a) (i) State Avogadro’s law of gaseous volume.

(ii) Find the volume of oxygen gas required to burn completely 1 dm³ of methane. CH4 + 2O  2(_g) ? CO  2 + 2H  2O. 

(iii) What is the volume of carbon dioxide formed in the reaction at (ii) (4 marks)

(b) Define the following terms:

(i) Mole

(ii) Molecular weight (2 marks)

4. (a) Ammonia gas can be prepared by heating an ammonium salt with an alkali

(i) Name the most common pair of reagents suitable for this reaction.

(ii) Write the equation for the reaction. (4 marks)

(b) Ammonia is very soluble in water and less dense than air. How does each of the properties determine the way in which ammonia is collected in a gas jar? 

5. (a) Differentiate empirical formula from molecular formula

(b) Calculate the empirical formula for a compound with the following composition: lead 8.32 g, sulphur 1.28 g, oxygen 2.56 g (relative atomic wt of lead = 207, sulphur = 32, oxygen = 16)

6. (a) Classify the following reactions into oxidation and reduction reactions.

(i)  S( s) + O 2( g) ? SO 2( g)

(ii) N2( g) + 3H 2( g) ? 2NH 3( g)

(iii) Fe2+ (aq) ­ e ­  ? Fe3+ (aq)

(iv) Fe³⁺ _(aq) ­ e  ^­  ? Fe²⁺ _(aq)  (4 marks)

(b) What is the oxidation number of iron in iron (III) chloride? (3 marks)

7.(a) Explain the meaning of the following:

(i) Malleable

(ii) Ductile

(iii) Brittle 

(b) Give an account of the following

(i) Anhydrous copper (II) sulphate becomes coloured when exposed to the air for a long time.

(ii) Carbon dioxide can be collected by the downward delivery method.

(iii) Concentrated sulphuric acid is not used for drying hydrogen sulphide gas.

(iv) Sodium metal is kept in paraffin oil. 

8. (a) (i) What is the first step to take when you want to identify the contents of a given salt containing one anion and one cation?

(ii) In a solution of water, identify a solute and a solvent. Justify your answer. 

(b) Sodium is a solid while chlorine is a gas at room temperature although they are in the same period in the periodic table. What is the cause of this difference?

9. (a) (i) Name three gases which should not be produced in order to prevent the destruction of ozone layer. 

 (ii) List and explain three effects of ozone layer depletion.

(b) Lack of safe water for domestic and industrial uses is a serious problem in most of Tanzanian towns. The major cause of this problem is pollution in the water sources. Slate three methods that could make water from a pond or a well be safe for drinking.

10. (a) (i) Name the products formed when nitrates of potassium and zinc decompose by heat. 

 (ii) Suggest why the nitrates of zinc and potassium behave differently on heating.

(b) Mention two uses of sodium nitrate.

11. (a) Which ways are the fossil fuels detrimental to the environment? Give four points. 

(b)  Briefly explain how biogas is produced by using domestic waste.

12. (a) (i)  Define isomerism.

(ii) Draw and name two structural formulae of the isomers of C4H8.

(b) Carbon dioxide can be prepared by adding an acid to calcium carbonate.

(i) Using a named acid, write a balanced chemical equation for the reaction. (ii) Name all the products formed in (b) (i)

SECTION C (15 Marks)

Answer one (1) question from this section.

13. Describe the cause, two effects and measures to be undertaken in order to prevent/reduce the amounts of acid rain.

14. 0.48g of a metal, M was placed in a test tube and hot copper (II) sulphate solution was added to it and stirred until the reaction stopped. The metal (M) displaced copper from copper (II) sulphate solution. Copper was filtered, washed with water, dried at 100⁰ C  and the mass found to be 1.27g. Given that, the balanced chemical reaction that occurred is M _(s)  + CuSO  _4(aq)  MSO  _4(aq)  + Cu  _(s) 

(a) Calculate;

1. The number of moles of copper that were formed and the number of moles of M that were used in the reaction.
2. The relative atomic mass of M and hence identify metal M.

(b) State the appearance of the metal formed (Cu).

(c) With ionic equations, explain why the reaction can be considered to involve both oxidation and reduction.