ReviseNow 1996 - Revise Now

PAPER 1

SECTION A:

Answer all questions from this section.

1. The atomic number of element A is 33.

(a)Write the electronic configuration of A

……………………………………………………………………………………………………………………………………………………………………………………………………

(b)Write the formula of the oxide of A

(c) State whether the oxide of A you have given in (b) is acidic, neutral, basic or amphoteric. Write an equation to illustrate your answer

2. (a)Dilute Sodium hydroxide solution was added dropwise until in excess to aqueous chromium(III)chloride.

(i)State what was observed

(ii)Write the equation for the reaction

(b)To the product in (a) was added a few drops of hydrogen peroxide and the mixture boiled.

(i)State what was observed

(ii)Write the equation for the reaction

3. Given the following electrode potentials.

chem_1996_no_3_paper_1

(a)Arrange the electrodes in order of reducing power starting with the least reducing

(b) (i) Which two electrodes will form a cell of maximum e.m.f

(ii)Write the cell notation for the cell you gave in (i)

(iii)Write the overall cell reaction for the cell in (i)

4. 8.0g of copper ore was leached with dilute sulphuric acid and the resulting solution diluted to 250cm3,to 30.0cm3 of this solution was added excess 10% potassium iodide solution. The liberated iodine required 23.5cm3 of 0.05M sodium thiosulphate solution for complete reaction. Calculate the percentage of copper in the ore. The reactions that take place are

chem_1996_no_4_paper_1

5. Name a reagent that can be used to distinguish between each member of the following pairs of compounds .in each case state what would be observed when the reagent is added to each compound.

reagent……………………………………………………………………………………………………………………………………………………………………………………………………

observation…………………………………………………………………………………………………………………………………………………………………………………………………

(b) CH₃CH₂CH₂NH₂ and CH₃CH₂CH₂NHCH₃

Reagent……………………………………………………………………………………………………………………………………………………………………………………………………

6. Ammonium chloride undergoes hydrolysis when dissolved in water according to the equation.

NH₄⁺(aq) + aq ⇄ NH₃(aq) + H⁺(aq)

If the hydrolysis content for ammonium chloride Kh ,at 25⁰C is 5.6x10^-10,calculate

(i)The pH of a 0.1M solution of ammonium chloride

(ii)the percentage hydrolysis of 0.1M solution of ammonium chloride

7. The general formula of a polymer A is.

(a) write the formula of the monomer of A

(b)Name the type of polymerization by which A is formed

8. (a)Define the term heat of precipitation.

(b) 25.0cm³ of 0.5M silver nitrate solution was added to 25.0cm³ of 0.5M sodium chloride solution in an insulated container. The temperature of the resulting mixture rose by 3⁰C.Assuming that the container had negligible heat capacity and the heat capacity of the resulting mixture is .4.2 jg^-10C^-1, calculate the heat of precipitation of silver chloride.

9. (a)A solution containing 4.50g of a solute B dissolved in 125g of water freezes at -0.372⁰C.calculate the formula mass of B.(K_t for water is 1.86⁰Cmol^-1 per 1000g).

(b)How do you expect the formula mass of B to change if it ionized in water? Explain your answer

SECTION B

Attempt six questions from this section.

10.(a) Name the type of crystal lattice formed by the following substances.

(i)iodine

(ii) Caesium chloride

(iii)silicon dioxide

(b)Arrange the substances given in (a) in order of increasing melting point

(c)Explain how the bonding in each of the compounds in (a) affect their melting points

11. (a) An organic compound M contains C,80%,H,7% the rest being oxygen. Calculate the empirical formula of M.

(b) 0.5g when vaporized at 150⁰C and 760mmHg occupies 144.6cm³ Determine the molecular mass of M.

(c) M burns with a yellow sooty flame, forms a yellow orange solid with Brady`s reagent and reacts with a solution of iodine in sodium hydroxide to form a yellow solid. Write the formula of M.

(d)Write the equation for the reaction between M and Brady`s reagent.

12. In the extraction of aluminium from bauxite, the crude ore is purified by first digesting with sodium hydroxide solution.

(a)Describe what takes place when bauxite is digested with sodium hydroxide and write equations for the reactions taking place

(b)Name the steps that are carried out after digesting the bauxite with sodium hydroxide

(c)Describe how pure aluminium is obtained from the purified ore

13. Using equations only show how the following conversions could be carried out.

……………………………………………………………………………………………………………………

14. Sulphur dioxide is oxidized to sulphur trioxide according to the equation.

2SO₂(g) + O₂(g) ⇄ 2SO₃(g).The enthalpy of the forward reaction at 25⁰C is -96kjmol^-1

(a)Describe giving the reasons the effect on the position of equilibrium of

(i)Increasing the temperature from 25⁰C to 100⁰C

(ii)Excess oxygen

(b) At 7000C and total pressure of one atmosphere the partial pressure vat equilibrium for sulphur dioxide and oxygen are 0.27 and 0.41 atmosphere respectively. Calculate the equilibrium constant, Kp, for the reaction

(c)How is sulphuric acid obtained from sulphur trioxide?

15. (a) Explain the term molar conductivity of an electrolyte.

(b)Sketch a graph to show how the molar conductivity or barium hydroxide varies with concentration in aqueous solution.

(c)Given the following molar conductivities at infinite dilution, Ʌo, calculate Ʌo for ammonia solution

Ba(OH)₂ Ʌo = 457.6 ohm^-1cm²mol^-1

Ba cl₂ Ʌo =240.6 ohm^-1cm²mol^-1

NH₄ Cl Ʌo =129.8 ohm^-1cm²mol^-1

16.(a)Write equations to show how each of the following compounds can be synthesized.

(i) chem_1996_no_16_a from benzene sulphonic acid

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

chem_1996_no_16_c

(iii) chem_1996_no_16_c

(b)Arrange the compounds X, Y and Z (in (a) above) in order of increasing acidity

17. (a)Sketch the shapes of the following molecules.

(i)NH₃

(ii)BF₃

(iii)H₂S

(b)Explain why each molecule adapts the shape you give in (a) above

NH₃

BF₃

H₂S

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PAPER 2

SECTION A

Answer three questions from this section

1. (a) (i)Define the term partition coefficient and state the conditions under which it is valid.

(ii)Briefly describe how the partition coefficient for the distribution of iodine between water and trichloromethane can be determined.

(b) (i) 60cm³ of an aqueous solution containing 0.3g of compound Y was shaken with 30cm³ of ethoxyethane and the mixture allowed to stand. Calculate the mass of Y which was extracted into the ethoxyethane layer.( the partition coefficient of Y between ethoxyethane and water is 4.7).

(ii)The aqueous solution in (i) was extracted with two successive 15cm³ of ether. Calculate the mass of Y that was extracted by ether.

(c) The table below shows the result of partition of aminomethane between trichloromethane and 0.1M copper(II)sulphate solution.

[(CH₃NH₂(0.1M CuSO₄)]	0..87	1.10	1.33	1.57	1.80
[CH₃NH₂(CHCl₃)]	0.02	0.03	0.04	0.05	0.06

(i)Plot a graph of [CH₃NH₂(0.1M CuSO4] versus [CH₃NH₂(CHCl₃)]

(ii)Determine the number of moles of aminomethane that has formed a complex with copper(II) ion.

(iii)Write equation for the reaction between copper(II) ions and aminomethane.

2. Complete the following equations and in each case outline a mechanism for the reaction.

chem_1996_no_2_paper_2

3. (a) State what would be observed and write equation for the reaction which takes place when dilute sodium hydroxide is added dropwise until in excess to

(i)Ni²⁺(aq)

(ii)Mn²⁺(aq)

(iii)Sn⁴⁺(aq)

(b)Discuss the reaction between the elements of group(VII) of the periodic table(fluorine, chlorine, bromine and iodine) and

(i)water

(ii) sodium hydroxide solution

4. (a) Ethanoic acid is a weak acid

(i)Explain what is meant by ‘weak acid’

(ii)Calculate the pH of a 0.05M ethanoic acid solution(Ka of ethanoic = 1.8x10^-5mol dm^-3 ) state any assumptions you make.

(b) (i)Explain what is meant by a buffer solution

(ii)Discuss the action of a buffer solution

(c) A solution was made by dissolving 7.2g of ethanoic acid and 12.0g of sodium ethanoate to make 1l solution. to the solution was added 0.8cm3 0f 1M hydrochloric acid.

Calculate the pH of the solution. State any assumptions you make

SECTION B

5. (a) Compound A,C₇H₁₄O₂ reacted with sulphuric acid on heating t form compounds B,C₄H₁₀O and C₃H₆O₂,B reacted with sodium effervescence but had no effect on litmus paper.

(i)Write the names and structural formulae of all the possible isomers of B.

(ii)Name a reagent that can be used to distinguish between the isomers in (i) and state what would be observed if the isomers are reacted with the reagent.

(b)B reacted with acidified dichromate solution to give D which formed a fellow solid when reacted with alkaline iodine solution.

(i)Identify B D and the yellow solid.

(ii)Name one reagent that can be used to identify the functional group in D.

(c)Write equations and indicate a mechanism for the reaction between B and

(i) concentrated orthophosphoric acid

(ii)ethanoyl chloride.

(d) C reacts with sodium carbonate with solution of a gas. Write the structural formula of A.

6. (a)What is meant by the term atomic radius?

(b)Explain how atomic radii vary

(i)along a short period of a periodic table

(ii) down the group in the periodic table

(c) Explain how the sizes of ironic radii of group II ions affects the properties of their compounds compared to those formed by group 1 metals.

7. (a) (i) What is meant by stability of nucleus.

(ii)Explain the factors that determine the stability of a nucleus.

(b)The graphs below show a plot of the number of neutrons versus the number of protons in stable nuclei

chem_21

(i)State what lines A and B represent

(ii)Describe briefly how nuclei X and Y can gain stability

8.(a)Explain the following processes as used in the extraction of metals.

(i)Flotation

(ii)Roasting

(iii)smelting

(b)Describe briefly how the percentage purity of an iron ore can be determined in the laboratory.

CHEMISTRY 1996