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KCSE Mokasa Chemistry Paper 1 Joint Exams and Marking Schemes Free Access

Name: …………………………………………………………………………Class: ………… Adm.No……………..

School: ………………………………………………………………………..Date: ………………Sign: ………………

233/1

CHEMISTRY

Paper 1

Time: 2 hours

M O K A S A 2 J O I N T E X A M I N A T I O N –

Kenya Certificate to Secondary Education

INSTRUCTIONS TO CANDIDATES

Write your name, admission number, date and school in the spaces provided.
Answer all the questions in the spaces provided.
All working must be clearly shown where necessary.
Scientific calculators may be used.

FOR EXAMINERS’ USE ONLY

1	2	3	4	5	6	7	8	9	10

11	12	13	14	15	16	17	18	19	20

21	22	23	GRAND TOTAL	%

This paper consists of 17 printed pages. Candidates are advised to check and to make sure all pages are as indicated and no question is missing.

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a) Define the term isomerism. (1mark)

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

b) Draw and name two isomers of C₄H₁₀(2 marks)

The figure below shows the behavior of emission from a radioactive isotope M. Use it to answer the questions that follow.

Explain why isotope M emits radiations (1 mark)

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

Name the radiations labeled P and J (1 mark)

P…………………………………………..

J…………………………………………..

Explain why radiation A is not deflected (1 mark)

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

68gof aluminiumsulphate were dissolved in 600cm³ of water, calculate the concentration of the sulphate ions in the solution. (Al=27,S=32,O=16) (3 marks)

a) Using an equation explain the observation made when concentrated nitric (V) acid is added into a beaker containing copper turnings. (2 marks)

b) What property of nitric acid is shown in the equation above? (1 mark)

An element Z is atomic number 13, Z reacts with both oxygen and chlorine. Explain why the oxide of Z has a melting point of 1020⁰C while the chloride of Z sublimes at 124^oC (2marks)

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

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

Ammonia gas

Drying agent

Heated black solid

Copper metal

Nitrogen

Name a suitable drying agent used in the process above (1mark)

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

Describe one chemical test for ammonia gas (1mark)

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

Name substance X (1mark)

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

Lead (II) nitrate solution forms a white precipitate when reacted with sodium hydroxide. The precipitate dissolves in excess sodium hydroxide to form a colourless solution.

Identify;
The white precipitate …………………………………………… (1mark)
Colourless solution ……………………………………………… (1mark)
Write an ionic equation for the formation of the colourless solution (1mark)

The set up below shows the investigation of the effect of a certain gas on heated iron powder. Use the diagram to answer the questions that follow.

Conc H₂SO₄

NaCl_(s)

Conc H₂SO₄

Combustion tube

Iron

Water

Heat

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

………………………………………………………………………………………………

State and explain the difference in the observation made if chlorine gas was used instead of the gas produced in the set up above. (2marks)

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

Identify the amendment that would be made in the set up above when chlorine gas is to be used. (1 mark)

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

Describe one chemical test that can be used in a school laboratory to distinguish between ethanol and ethanoic acid. (2mark)

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

The diagram below shows a piece of heating apparatus. Study it and answer the questions that follow.

Name the parts labeled L and M (2marks)

L………………………………………………………………………….

M…………………………………………………………………………

State the function of the parts labeled K (1mark)

Hydrazine gas N₂H₄ burns in oxygen to form nitrogen gas and steam.
Write a balanced chemical equation when hydrazine burns in oxygen (1mark)

Use the bond energies given below to calculate enthalpy change for the reaction in (a) above. (3marks)

Bond

Bond energy (kJmol^-1)

N N

N H

H H

O O

944

163

388

496

463

A form four students accidentally mixed the following: iron filling, sodium chloride, aluminium chloride and copper (II) oxide. Describe how the student can obtain a pure sample of sodium chloride crystal. (3marks)

Explain how a student can prepare a crystal of silver nitrate in the school laboratory starting with silver metal. (3marks)

A ²⁺_(aq)+ 2e^–A_(s)-2.72

B ²⁺_(aq)+ 2e^–B_(s)-1.78

C ⁺_(aq)+ e^–C_{2 (g)}0.00

D ²⁺_(aq)+ 2e^–D_(s)+0.34

F_{2 (g)}+ 2e^–F ^–_(aq)+2.44

E^θVolts

Use the standard electrode potential below to answer the questions that follow. The letters do not represent the actual symbol of the elements.

Identify element C (1mark)

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

Draw a well labeled diagram for the electrochemical cell formed when the half cells of A and B are combined. (3marks)

Carbon (II) oxide was passed over heated lead (II) oxide in a combustion tube as shown in thediagram below.

Lead (II) oxide

Dry

Carbon (II) oxide

Heat

Tube A

Calcium hydroxide

State the observation made in tube A (1mark)

…………………………………………………………………………………………………

Write a well-balanced chemical equation for the reaction that took place in the combustion tube. (1mark)

Graphite is one of the allotropes of carbon:
Name one other element that exhibits allotropy (1mark)

………………………………………………………………………………………

Give a reason why graphite is an ideal lubricant than ordinary oil (1mark)

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

a) State the Grahams’ law of diffusion (1mark)

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

b) In an experiment 60cm³ of a gas Q diffuse through a porous plate in 10 seconds. Another gas P diffuse through the same plate in 30 seconds. Given that the density of gas Q is 25g/cm³, calculate the density of gas P. (3marks)

An element Q reacts with excess oxygen to form a yellow solid.
Write a balanced chemical equation for the reaction between Q and water. (1mark)

State one observation made when Q reacts with water (1mark)

………………………………………………………………………………………………

Study the graph below and answer the questions that follow. The letters do not represent the actual symbols of the elements.

100

200

300

400

500

600

Atomic number

Ionization

energy

What is meant by the term ionization energy? (1mark)

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

What is the general name given to the group in which elements P,Q and R belong to (1mark)

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

Explain why R has the lowest ionization energy (1mark)

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

Hydrogen chloride gas was bubbled into three boiling tubes A, B and C containing methylbenzene, distilled water and excess sodium hydroxide solution respectively. A piece of magnesium ribbon was then added into each boiling tube. State and explain the observations made in boiling tubes A and B. (3marks)

Boiling

tube

Observation

Explanation

An element C reacts moderately with an acid to produce hydrogen gas. It also reacts with

steam to form a black solid and hydrogen gas.

State the name of the name of the product formed when C is exposed to moist air (1mark)

………………………………………………………………………………………

Write the equation for the reaction between C and steam. (1mark)

The figure below represents extraction of sulphur by frasch process.

Ground level

Identify the substance carried through pipe X (1mark)

…………………………………………………………………………………………………

State two properties of molten sulphur that make it possible for sulphur to be extracted by the method shown above. (2 mark)

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

Explain why sulphur is not extracted by open cast mining method. (1mark)

Metallic cup

Ag_(s)

Ag⁺_(aq)

The set up below was used by Anthony a form four student who wanted to electroplate his metallic cup with silver. He passed a current of 2A for 2 hours.

If the initial mass of the cup was 98g, determine the mass of the cup after the 2hours (1F=96,500C Ag=108) (3marks)

State one importance of electroplating (1mark)

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

Study the diagram below and answer the questions that follow.

Dry Chlorine gas

Dry flower petals

Fresh flower petals

Chlorine gas

State and explain the observations made in gas jar A and B (3marks)

Gas jar	Observation	Explanation
A
B

Write the chemical equation that occurs in gas jar B (1mark)

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

Ore

Oxide X

Metal X +Hydrogen gas

Salt solution

Colourless solution

CO₂

Heat

HCl_(aq)

Excess NH_{3 (aq)}

Name the chief ore from which metal X is extracted (1mark)

………………………………………………………………………………………………

Name the main cation in the colourless solution (1mark)

………………………………………………………………………………………………

Write the chemical equation for the reaction between the oxide of X and carbon (II) oxide when heated. (1mark)

Time (sec)

In an experiment magnesium ribbon was reacted with dilute hydrochloric acid and the volume of hydrogen gas produced with time recorded. The graph below shows the volume of hydrogen gas produced against time.

Volume of hydrogen m³

Explain the following observations:

The curve is steep at the beginning (2mark)

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

The curve flattens at region AB (1mark)

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

On the same axis plot the curve that would be obtained if the acid used was ethanoic acid in place of hydrochloric acid (1mark)

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