FORM SIX CHEMISTRY NECTA 2013

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: 2013

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.;

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

Rydberg constant, RH;=;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

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;

1.;;Differentiate nuclear reaction from chemical reaction.;

(b);;Complete the following nuclear equation:

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(c) The following figure shows the mass spectrum of lead. The highest peaks and the mass numbers of the isotopes are shown. Calculate the average atomic mass of lead.

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2.;;(a) Lyman discovered a series of spectral lines for hydrogen in the ultra-violet region of the electromagnetic spectrum. What value must n1 have for this series? Give a reason for your answer.

(b);;;;;;Calculate the energy of a line in the Lyman series with ni = land n2 = 00.

(c) An experimental iodine laser emits light of wavelength 1.315gm. Calculate the frequency of this light and the energy per photon.

3.;;Predict the hybridization of the following:

(i);;;;;;PCl5

(ii);;;SF6

(iii);CO2

(iv);BC13

(b);;;;;;Arrange the following substances in order of increasing melting points:;

C02, H20, CO, H2;and Ar.

(c) Use VSEPR theory to predict the molecular geometry of the species PCL, NH3;and PC15.

4.;;State two characteristics of compounds which are suitable for steam distillation.

(b);;;;;;An aromatic compound Z was steam distilled at 98.60;C and 1 atmospheric pressure. The distillate was found to contain 25.5 grams of water and 7.4 grams of aromatic compound Z. Given that the saturated vapour pressure of water at 98.60C is 720mmHg, calculate the relative molecular mass of the aromatic compound.

(c);;;;;;Benzene (C6H6) and toluene form a nearly ideal solution. At 313K the vapour pressure of pure benzene is 150mmHg and of pure toluene is 50mmHg. Calculate the vapour pressure of a mixture of these two liquids containing equal masses at the given temperature.

5.;;Define the following:

(i);;;;;;;Molar volume of a gas at s.t.p

(ii);;;;;;Dalton's law of partial pressure.

(b);;;;;;Two has burettes, one containing 10cm3;of sulphur dioxide (S02) and other containing 30cm3;of hydrogen sulphide (H2S) both at I atmosphere and at OOC are initially separated by a stop cork. The stop cork is then opened and the two gases are allowed to mix according to the reaction SO2(g);+ 2H2S(S)→3S(s);+ 2H20(l)

Calculate the final pressure (in atmospheres) after the reaction has ended and the apparatus has regained its temperature of OOC. (Assume liquid water does not exert pressure).

6.;;Distinguish between the following:

(i);;;;;;Reaction quotient and equilibrium constant.

(ii);;;;Chemical equilibrium and physical equilibrium.

;(b) (i) The Kc value for the reaction 2NO(g);+ Cl2;;;2NOCl(g);is

4.6x 104;dm3;moElat 298 Kelvin. Calculate the KP value for this equilibrium.

(ii) Calculate the KP value for the equilibrium 2NOC12(g);2NO +Cl2(g);;at 298 Kelvin.

(c);;(i) For equilibrium reaction N2(g) +3H2(g);;2NH3(g);derive KP and Kc relationship if the pressure of the mixture is PT;and volume is VT.

SECTION B

7.;;;(a) Three elements; F, G, and H have atomic numbers 17, 18 and 19 respectively.

(i);;;;Write electronic configuration of each element.

(ii);;;;;What type of ion each element is expected to form?

(iii);;;;In which group and period would each element be placed?

(b);;;;;Study the following hypothetical elements in a periodic table and then answer questions that follow.

Using letters indicated in the table, identify the following:

(i);;;;;The element which is the most electronegative.

(ii);;;;;A pair of elements that is likely to form the strongest electrovalent bond.

(iii);;;Two elements which are likely to have strongest reducing properties.;

(iv);;;Two elements which form neither negative nor positive ions.

8.;;(a) With reference to Modern periodic table, briefly explain the following

(i);;;;;Diagonal relationship.

(ii);;;;Anomalous behaviour

(b);;;;;Explain how the hydrides of period 3 elements react with water.

(c);;;;;;The following are;some oxides of elements Of;;period;;;;3:

Nap,;;A1203, P205, Si02;and MgO. Arrange them in the order of

(i);;;;;;;Increasing in basic characters

(ii);;;;;Decreasing in ionic characters

9.;;(a) (i) What is the difference between the first and the second ionization energies of electron?

(ii) The first and the second ionization energies for the sodium atom are 493kJ and 4560kJ respectively. Account for such a big difference between the two ionization energies.

(b);;;;;By using chemical reactions, show how sodium reacts with the following:

(i);;;;;;;ethanol (ii) ammonia (iii) oxygen;;;;;;;;;;(vi) water

10.;;;;;;(a) State the law of mass action.

(b);;;;;One mole of PCI5 was introduced into a closed vessel ata certain temperature. By the time equilibrium was established, it was found that PC15 was 10% dissociated and the total pressure in the vessel was 4 atmospheres. Calculate:

(i);;;;;;;KP value at the temperature of the experiment

(ii);;;;;The total pressure at which PC15 was 20% dissociated.

11. (a) Complete the following equations for reactions of the alkanes:

;(b);;;;;;Write any three structural isomers of alkylicyclohexane of molecular formula C6H12.

(c);;;Write equations for the preparation of alkenes from the following starting materials, indicate the conditions required and if there is more than one product, indicate which one is major.

12.Write the Structure of the functional groups of the following sets of compounds:

1. Alkanes;;;;;;;;;;;;;;;;;;;;;;;;;;;; (ii) alkenes

;;;;;(iii) alkynes;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;(iv) alcohols

;;;;;(v) ketones;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;(vi) aldehydes

;;;;(vii) carboxylic acid;;;;;;;;;;;;;;;;;(viii)tertiary amines

(b) Give the IUPAC name of the following compounds

13.;;;;;With support of chemical reactions show how the following compounds can be prepared from ethanol as source of carbon atoms:;

(a);;;;;;;;Benzene

(b);;;;;;;Ethyl benzene

14.;;;;;(a) Write the structure of the major products for the reaction of gaseous hydrogen bromide with the following:

;(b);;;;;;;Explain how you can distinguish the following:

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