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KCSE CLUSTER TESTS 20

Chemistry Paper 2

1.

i) Work out the activation energy for the reaction. (1mk)

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ii) Calculate the heat of formation of HF. (1mk)

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iii) Is the reaction endothermic or exothermic. Give a reason for your answer.

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b) In an experiment to determine the heat of combustion of methanol, CH3OH, a student set-up the apparatus as shown below. Study the set-up and the data below and answer the questions that follow

DATA

Volume of water=400cm3

Final temperature of water=350C
Initial temperature of water= 250C

Final mass of lamp +Methanol=35.40g

Initial mass of lamp +Methanol =35.90g

Density of water=1.0g/cm3 Specific heat capacity of water=4.2jg-1 0c-1

b) Write an equation for the combustion of methanol.

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c) Calculate:

i) The number of moles of methanol used in combustion (C=12; O=16.0; H=1.0)

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ii) The heat change in the experiment.

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iii) The heat change when one mole of Methanol was burnt completely.

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d) Explain why the value of Molar heat of combustion for Methanol obtained in this experiment is different from the theoretical value.

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f) Draw on the grid below an energy level diagram for the combustion of Methanol.

11 marks

2.

Study the flow chart below and answer the questions that follow.

a) Write the structural formular of propane. (1mk)

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b) State the reagents and conditions necessary in

i) Step VII Reagent ( ½ mk) Condition ( ½ mk) …………….... …………………………… …………………………

ii) Step II Reagent ( ½ mk) Condition ( ½ mk) ………………. …………………………… ………………………..

c) Identify the following substances L

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d) Write equations taking place in steps

i) III

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ii) V

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e) Name the process that takes place in step

i) IV

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ii) V

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f) The following structures represent P Q and R.

Which of the detergents is;

i) The worst pollutant? Explain

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ii) Unsuitable to use when washing clothes with hard water? Explain.

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13 marks

3.

The grid below is part of the periodic table. Study it carefully and then answer question given thereafter. The letters do not represent actual chemical symbols of the elements.

a) Select the element which is the strongest reducing agent. Give a reason for your answer.

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b) An element P forms an ion P- with electronic configuration 2.8.18.8. Place element P on the grid provided above.

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c) Compare the atomic radii of elements Q and X. Explain your answer.

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d) Write a chemical equation to show the effect of heat on the nitrate of element N.

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e) Why is element L used in light bulbs.

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f) The electrical conductivity of element Q is higher than that of element M. Explain

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g) When 6.0dm3 of chlorine gas were completely reacted with element N 23.75g of the product were formed. Determine the relative atomic mass of element N [Cl=35.5; Molar gas volume at r.t.p =24.0dm3 mol-1]

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11 marks

4.

a) The set up below was used during the electrolysis of 6M hydrochloric acid using inert electrodes

i) Identify the anions and cations present in the solution.

Anions:

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Cations:

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ii) Give a reason why a mixture of gases are obtained at electrode B. Explain your answer

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iii) During the electrolysis, a current of 2 amperes was passed through the solution for 3 hours,20 minutes. Calculate the volume of the gas produced at electrode A (1 Faraday =96500 Coulombs and molar gas volume at room temperature is 24000cm3)
b) Name one applications of electrolysis

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c) Use the information below on standard electrode potentials to answer the questions that follow:

i) From the list select:

I. The strongest reducing agent. Give a reason

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II. The strongest oxidizing agent. Give a reason

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ii) Calculate the e.m.f of the cell constructed in (i) above.

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12 marks

5.

In an experiment to study the rate of reaction between a metal carbonate of MCO3 and dilute hydrochloric acid. 1.0g of the carbonate were reacted with excess of the acid. The data in the table below was recorded. Use it to answer the questions that follow.

a) i) On the grid provided plot a graph of total volume of carbon (IV) oxide produced against time.

ii) From the graph determine the volume of carbon (IV) oxide produced after 45 seconds.

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b) Determine the rate of reaction between 90th second and 120th second.

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c) On the same grid sketch the curve that would be obtained if powdered carbonate was used.

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d) i) Dilute sulphuric acid cannot be used in this experiment. State and explain the possible identity of the metal carbonate.

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ii) State and explain how the rate of reaction changes as the reaction proceeds.

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11 marks

6.

a) Study the scheme below and answer the questions that follow.

i) Write the formula of the cation present in solution F.

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ii) What property of Chlorine is shown in step I

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iii) Write an equation for the reactions taking place in steps II and III.

Step II

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Step III

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vi) Explain why Fe2+ solution slowly changes colour to brown when exposed to air for sometime.

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b) A student set up the following apparatus for preparing gas jars of dry ammonia gas

(i) Complete the diagram to show how dry ammonia gas could be collected.

(ii) Write an equation that produces ammonia gas from the set up above.

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(iii) Dry ammonia was passed over 2.4g of hot copper (ii) oxide in a combustion tube for some time.

I) State and explain the observations made in the combustion tube.

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II) Calculate the volume of ammonia gas that reacted at STP. (Cu=64, O=16,H=1,N=14, molar gas volume at STP=22.4litres)

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12 marks

7.

a) The flow chart below outlines some of the process involved during extraction of copper from copper pyrites. Study it and answer the questions that follow.

Identify:

i) Gas K

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ii) Gas P

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b) Write equations for the reactions that takes place in the

i) 1st Roasting furnace

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ii) Absorption tower

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c) i) Write the formula of the cation present in the slag M

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ii) What name is given to the reaction that takes place in chamber N? Give a reason for your answer.

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d) i) Name catalyst Y

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ii) Given that the mass of copper obtained from the above extraction was 210kg, determine the percentage purity of the ore (copper pyrites), if 810kg of it was fed to the 1st roasting furnace (Cu=63.5,Fe=56.0,S=32.0)

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10 marks

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