THE UNITED REPUBLIC OF TANZANIA NATIONAL EXAMINATIONS COUNCIL OF TANZANIA ADVANCED CERTIFICATE OF SECONDARY EDUCATION EXAMINATION

132/1 CHEMISTRY 1

(For Both School and Private Candidates)

Time: 3 Hours Year: 2015

Instructions

1. This paper consists of sections A and B with a total of ten (10) questions.;

2. Answer all questions in section A and two (2) questions from section B.

;3. Each question carries ten (10) marks in section A and fifteen (15) marks in section B.

;4. Mathematical tables and non-programmable calculators may be used.;

5. Cellular phones and any unauthorised materials are not allowed in the examination room.;

6. Write your Examination Number on every page of your answer booklet(s).

7.;;For calculations, you may use the following

Rydberg constant, R_H;=;1.09678x 10⁷m^-1

Gas constant, R = 8.31JmoI^-;¹;K;^-I;or 0.0082 atm mol^-1;K;^-I;dm³

GMV;;at s.t.p.;;;;22.4dm3

1 litre = 1 dm³;=1000cm³

At STP: Temperature = 273K, Pressure = 760mmHg

Planck constant, h=6.63x 10;^-34;Js

Velocity of light, C = 3.0 x 10⁸;m/s

Atomic masses H = 1, C = 12, N = 14, O-16, Na-23

;

1.;;;;;;;(a) State the following:

(i);;;;;;;;Pauli's exclusion principal

(ii);;;;;;Aufbau building principal.

(iii);;;;;Hund's rule of maximum multiplicity.

;(iv);;Half-filled and full-filled orbital rule.

(b) Write down the electronic configuration of each of the following species using orbital diagrams:

;(i) Cl-

(ii) K

(iii) Ca²⁺

(iv) F

;(c) Element Z occurs naturally as a mixture of;⁶⁹Z and;⁷¹;Z.

(i);;;;;;Briefly explain the significance of the numbers 69 and 71 and give a term which describes these two components in the natural element.

(ii);;;;If;⁶⁹Z and;^{7 I};Z have relative atomic mass of 69.8, find the percentages of;⁶⁹Z and;^7IZ in a sample of Z.

2.;;;;;(a) State the distribution law.

(b);;;The concentration of a solute X in water was found to be 8.5g/dm³;at room temperature. 100cm³;of this solution was shaken with 50cm;³;of methyl benzene until equilibrium was obtained. The organic layer was separated and found to contain 0.8g of X.

(i);;;;Calculate the distribution coefficient of X between methyl benzene and water.

(ii);;;What further mass of X would be removed from the aqueous layer if it was shaken with a further 50cm³;of methyl benzene?

(iii);;;;;Calculate the mass of X extracted if IOOcm;³;of methyl benzene was used at once instead of using 50cm³;twice. Which is the more efficient extraction process? Give reason for your answer.

3.;;(a) Describe two assumptions of kinetic theory of gases that are not obeyed by real gases.

(b);;;(i) Differentiate between diffusion and effusion for gases.

(ii) Uranium and fluorine form a gaseous compound UF6. It is proposed that the

²³⁵U and;²³⁸U isotopes be separated by gaseous diffusion of the;²³⁵UF and

²³⁸UF compounds. Which gas would diffuse more rapidly, and how much?

(c) A general equation for the breakdown of glucose in a human body can be presented as follows:

C₆H₁₂0₆;+60₂;+6H₂0. If 856 g of C₆H₁₂0₆;is consumed by a person over a certain period, what is the mass of C0₂;produced.

4.;;;;;;;;;(a) Write the equilibrium constant expressions (Kc) for the following reactions:

;(b);;;;;The equilibrium constant (Kc) for the reaction;is;at 25;⁰;C. What is the value of KP at this temperature?

View Ans

(c);;;;;;The following constants have been determined for hydrosulphuric acid at 25;⁰;C.

Calculate the equilibrium constant for the following reaction at the same temperature:

5.;;(a) 60cm;³;of a certain gas was collected at 60;⁰;C and;1.05 X 10⁵Nm^-2;. Calculate the volume of the gas at stp.

(b);;;;;When 0.5dm;³;of 02 and 1.0dm;³;of C02 were mixed at 27;⁰;C, the total pressure in the vessel was found to be 1.2atm. calculate:

(i);;;;;;;Partial pressure of each gas

(ii);;;;;The mass of each gas

6.;;;;;;;;;(a) Give ant four differences between a positive and a negative non-ideal solutions.

(b);;;;;Equal moles (0.5 moles) of benzene and toluene were mixed to form an ideal solution. Calculate the fraction of benzene and toluene in the second vapour given that P}nz = 95.1mmHg and =28.4mmHg

SECTION B

7.;;(a) 0.01M aqueous solution of 92.5% NaCl is dissociated at 18⁰C. Calculate the osmotic pressure(n) of this solution at the given temperature.

(b);;;;;When 5.8g of acetic acid (CH₃C0₂H) was dissolved in 90g of benzene (C₆H₆) the freezing point depression was found to be 3.8⁰C. Calculate the degree of association of acetic acid in benzene, given that acetic acid dimerizes in benzene and Kf =5.1;⁰C mol-I kg

8.;;(a) State Hess's law of constant heat summation.

(b);;;(i) Give the difference between the standard bond dissociation energy and the standard heat of formation of a substance.

(ii);;;;;;Calculate the enthalpy change for the reaction;

2NH₃;;;;;2(g) +3H₂(g) given

that:;;;;;

9.;;(a) Giving examples, briefly explain each of the following:

;(i) Hydrogen bonding;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(ii) Coordinate bond

(iii) Van der Waal forces

(b);;;;;For each of the following pairs of substances, predict which substance has a higher melting point, and give reason for each choice you make. (i) CH3CH3 and CH30H C02 and H2

(iii);;;;HCI and H20;;;;;(iv) Al and Mg (v) Si and Na

(c);;Describe the hybridization of beryllium in beryllium chloride (BeC12).

10.;;;;;(a);;Distinguish between the following: (i) atomic number from mass number (ii) a photon from a quanta.

(b);;;;;A photon was absorbed by a hydrogen atom in its ground state and the electron was promoted to the fifth orbit. When the excited atom returned to its ground state, visible radiation and other quanta were emitted.

(i);;;;;;;Briefly explain the transitions made by the electron for the excited atom to return to its ground state.

(ii);;;;;Calculate the wavelength of a photon emitted during a transition from the n1

= 5 state to the n2 = 2 state in the hydrogen atom given that AE = 2.18x10^-38

;

SECTION C

11.;;;;;(a);Briefly explain each of the following as applied in organic reactions

(i) Positive inductive effect. (ii) Negative inductive effect (iii) Mesomeric effect (iv) Stearic factors

(b);;;;;;Explain each of the following observations:

(i)Addition reactions in benzene need high energy.

(ii) Nucleophilic substitution reactions in benzene are not possible.

(iii);;;Methly group when attached to benzene ring direct another incoming group to ortho or para position.

(iv);;;;Nitro group when attached to benzene ring direct another incoming group to meta position.

12.;;;;;Give the mechanism for the following:

(a);;;;;;;Sulphonation of benzene

(b);;;;;;Chlorination of benzene

13.;;;;;(a) Write the mechanism ofthe following substitution reaction, indicating clearly the nucleophile, substrate and the leaving group:

;(b);;;;;;Carry out the following conversions:

(i);;;;;;;;Propane to I-chloropane.

(ii);;;;;;Propane to propene

(c);;;;;;;Complete the following reactions and name the organic product formed.

14. (a) Write the open structures of five isomers of the compound C₅H₇Cl and their corresponding IUPAC names.

(b);;;;;;Arrange the following compounds in the order of increasing acidity and reason(s) for your arrangement:

;(c);;;;;;Suggest suitable tests to distinguish the following compounds:;

(i);;Propyne and propene

(ii);;;2-methylpent-2-ene and 3-methlpent-2-ene

(iii);But-2-yne and butane

;