Revision Exams For Chemistry KCSE Mokasa

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CHEMISTRY

Time: 2 Hours

MOKASA II EXAMINATIONS

CHEMISTRY PAPER TWO

Instructions to students:

Write your name, admission number and class in the spaces provided.
Answer all questions in the spaces provided
This paper consists of 12 printed
Candidates should check the question paper to ascertain that all the pages are printed as indicated and that no questions are missing.
Candidates must answer all questions in English

Question	MaximumScore	Student’sScore
1	12
2	11
3	12
4	13
5	11
6	11
7	09
TOTALS	80

(a) Use the standard reduction potentials given below to answer the questions that follow.

Half –cell reactions E⁰(V)

B²⁺_(aq) + 2e^– B_(S) – 0.44

A²⁺_(aq) + 2e^– A_(S) – 0.76

C_2(aq) + 2e^– 2C^–_(aq) +0.54

2E⁺_(aq) + 2e^– E_2(g) 0.00

D³⁺_(aq) + 3e^– D_(S) -1.66

Identify the strongest oxidizing agent. Give a reason. (1mk)

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

Arrange the elements having the negative standard reduction potentials in order of increasing reactivity. (2mks)

…………………………………………………………………………………………………

Calculate the m.f of a cell formed by combing the half-cells of B and D. (2mks)

…………………………………………………………………………………………………

Write down the overall equation for the reaction taking place in (iii) above. (1mk)

Draw an electrochemical cell represented by the cell notation A_(s) / A²⁺_(aq) // B²⁺ / B_(S).

(3mks)

Draw a well–labeled diagram to show how a spoon made of D is electroplated using A. (3mks)

(b) Determine the oxidation state of Mn in MnO₄^– (1mk)

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

Study the flow chart below for the extraction of aluminium from ore.

Name the chief ore from which aluminium is extracted. (½ mk)

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Give two impurities present in the ore. (1mk)

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Briefly explain how the impurities in (ii) above are removed. (2mks)

Identify: (1mk)

Solution F…………………………………………………………………………………….

Residue S…………………………………………………………………………………….

Write balanced equations for
The reaction taking place in process X (1mk)

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

Reaction producing gas F (1mk)

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

State any one uses of aluminium (½ mk)

Compare the atomic radius of aluminium with that of sodium.(Al = 13, Na = 11). (2mks)

Aluminium reacts with chlorine to form a molecular compound. Using dots ( ) and (X) to represent electrons. Show the bonding in the compound formed. (Al = 13, Cl = 17)

(2mks)

(a) Define the term “Dynamic Equilibrium”. (1mk)

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

(b) List two factors, other than concentration, that affect chemical equilibrium. (1mk)

(d) Consider the reaction below an equilibrium.

Br_2(g)+ H₂O_(l) 2H⁺_(aq) +OBr^–_(aq) +Br^–_(aq)

(Orange)(Colourless)

State and explain the observation made when sodium hydroxide solution is added to the equilibrium mixture. (2mks)

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

(II) The flow chart below shows some of the process involved in the large scale manufacture of sulphuric (VI) acid. Study and use if to answer the questions that follow.

Why is the process referred to as Contact Process? (½mk)

Identify (2mks)

Solid C………………………………………………………………………………………..

Gas M…………………………………………………………………………………………

Gas L………………………………………………………………………………………….

Liquid V………………………………………………………………………………………

Write down the equation for the reaction taking place in the absorption tower. (1mk)

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Other than recycling, describe how pollution can be minimized in the process. (1mk)

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15,000 litres of sulphuric (IV) oxide is reacted in chamber Y. With an efficiency of 80% determine the final mass of sulphuric (VI) acid produced in (2 ½mks)

(MGV= 24 L)

(a) In an experiment to determine the heat of methanol, a student set up the apparatus as shown below. Study the set up and use the data obtained to answer the questions that follow.

100cm³

X XXXXX

Initialtemperature of water = 22⁰C

Finial temperature of water = 36⁰C

Initial mass of lamp + methanol = 85.10g

Final mass of lamp + methanol = 84.75g

Density of water = 1g/cm³ C = 4.2 Jg^-1k^-1

Determine the heat change for this experiment. (1mk)

Determine the molar enthalpy of combustion of methanol. (2mks)

Write down a thermochemical equation for the reaction. (1mk)

………………………………………………………………………………………………………………….

Draw an energy level diagram for the reaction. (2mks)

The molar enthalpy of combustion of thane (C₂H₆) is –1560kJmol^-1. Explain which one is a better fuel methanol and ethane.

(C= 12, O = 16, H = 1) (2mks)

(b) Use the information below to answer the question that follows

Ca_{(s )}+ ½ O_2(g)CaO_(s) ∆^H₁ = – 635kJmol^-1

C_(s) + O_2(g)CO₂(g) ∆^H₂ = -394kJmol^-1

Ca (s) + C(s) + ³/₂O_2(g)CaCO_3(S) ∆^H₃ = – 207kJmol^-1

Name two enthalpy changes represented by ∆^H₂(2mks)

Use the information above to calculate the enthalpy change for the reaction (3mks)

CaO_(s) + CO_2(g)CaCO_3(s)

………………………………………………………………………………………………………………….

Study the set-up below and use it to answer the questions that follow.

Calcium hydroxide

Flame

Copper (II) oxide

Carbon (II) oxide

State the observation made in the combustion tube. (1mk)

Write an equation for the reaction producing the flame. (1mk)

………………………………………………………………………………………………………………….

Explain the observation made in the conical flask when the experiment is done for a longer period of time (2mks)

The flow chart below show the manufacture of sodium carbonate. Study it carefully and answer the questions that follow.

Identify (1_½mks)

Gas X……………………………………………

Gas Y…………………………………………….

Liquid Q…………………………………………

Give one use of calcium chloride. (_½mk)

………………………………………………………………………………………………………………….

Write balanced chemical equations for the reactions in (2mks)

Chamber III

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

Chamber IV

………………………………………………………………………………………………………………….

Give two reasons why the Solvay process is considered one of the most efficient industrial process? (2mks)

………………………………………………………………………………………………………………….

Name two process taking place in chamber II. (1mk)

Study the flow chart below and use it to answer the questions that follow.

Give the names of substances (2mks)

N…………………………………………………………………………………………………..

F…………………………………………………………………………………………………..

A………………………………………………………………………………………………….

E…………………………………………………………………………………………………..

Give the conditions necessary for: (1_½mks)

Process I

Process IV (_½mk)

Draw the open structural formula of (1mk)

Write balanced chemical equations for the reaction in

Process II. (1mk)

………………………………………………………………………………………………………………….

Between E and magnesium. (1mk)

………………………………………………………………………………………………………………….

Name: (1_½mks)

Process (I)………………………………………………………………………………………

Process (III)……………………………………………………………………………………….

Process (IV)………………………………………………………………………………………

Give one distinguishing property of substance (_½mk)

………………………………………………………………………………………………………………….

State two ways in which polymers K has improved human life. (2mks)

………………………….……………………………………………………………………………………………………………………………………………………………………………………………………….

Study the flow chart below and use it to answer the questions that follow.

Identify the anion and cation in solution K

Cation ………………………………………………………. (1mk)

Anion……………………………………………………. (1mk)

Name the white precipitate (1mk)

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

Name the type of reaction in step 2. (1mk)

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Name any other solution that would form white ppt T in step 3. (1mk)

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Write the formula of the complex ion in solution (1mk)

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Describe how a dry sample of the salt forming the white ppt T can be prepared in the laboratory starting with barium oxide.

(3mks)