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Chemistry KCSE Mock Exams and Answers {Latest Best Collections}

MOCKS 1

NAME ______________________________________ INDEX NO _____________________

DATE ____________________________ SIGN ______________________________

233/1

CHEMISTRY

PAPER 1

TIME 2HRS

Element K has atomic number 20 while element M has atomic number 8.
Write the electron configuration of K and M

K ______________________ (1mk)

M ______________________ (1mk)

Write the symbol of the most stable ion of K and M

K ____________________________ (1/2 mk)

M ___________________________ (1/2mk)

Molten lead (ii) iodide is electrolyzed using inert electrodes. Write the half equation of the reactions that occur at the anode and cathode.
Anode _______________________________________ (1mk)
Cathode ______________________________________ (1mk)
b) Explain why the conductivity of metals decrease with increase in temperature

________________________________________________________________________

Some sodium chloride was found to be contaminated with copper (ii) oxide. Describe how a sample of dry sodium chloride can be obtained from the mixline

________________________________________________________________________

Hot platinum wire was lowered into a flask containing concentrated ammonia solution as shown below

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State and explain the observations made (3mks)

________________________________________________________________________

a) What is a dative boud? (1mk)

________________________________________________________________________

b) Draw a dot (.) and cross (x) diagram to show bouding in carbon (ii) oxide (2mks)

Air was passed through several reagents as shown in the flow chart diagram

What is the purpose of concentrated potassium hydroxide solution? (1mk)

________________________________________________________________________

Write an equation for the reaction which takes place in the chamber with magnesium powder (1mk)

________________________________________________________________________

Name one gas which escapes from the chamber containing magnesium powder (1mk)

________________________________________________________________________

Name the following substances
CH₂CH CH₂CH₃ ______________________________________ (1mk)
CH₃CHCHCH₂CH₃ _______________________________________ (1mk)
State the observation made when compound in (a) above was passed through acidified potassium (vii) manganite (1mk)

________________________________________________________________________

The diagram below shows a wooden splint that was placed horizontally across the middle part of a non-luminous flame.

Explain the observation made (2mks)

_____________________________________________________________________

________________________________________________________________________

Explain why non-luminous flame is preferred for heating than luminous flame (1mk)

_____________________________________________________________________

________________________________________________________________________

Explain giving reasons why?
Sulphuric(vi) acide is not used with marble in the preparation of carbon(iv) oxide (2mks)

_____________________________________________________________________

________________________________________________________________________

Water cannot be used to extinguish oil fire

________________________________________________________________________

15cm³of a solution containg 2.88g/dm³ of an alkali XOH completely reacts with 20.0cm³ of 0.045m sulphuric(vi) acid. Calculate the molarity and relative atomic mass of x present in the alkali

________________________________________________________________________

An hydrocarbon Q was found to decolourise potassium manganate(vii)solution. When two moles of Q were burnt completely six moles of carbon(iv)oxide and six moles of water were formed.
Write the structural formula of Q (2mks)

________________________________________________________________________

Name the homologous series to which Q belongs

________________________________________________________________________

The diagram below represents an electrochemical cell

i) On the diagram label the salt bridge (1mk)
ii) State two observations made in cell B (1mk)

________________________________________________________________________

Write the overall ionic equation of the cell (1mk)

________________________________________________________________________

During the extraction of copper and zinc from their ores, some of the processes include
Crushing
Mixing of the crushed ore with oil and water and bubbling air through it.

(i) Name the process (ii) above (1mk)

________________________________________________________________________

(ii) What is the purpose of (ii) above

________________________________________________________________________

Dry chlorine gas was passed through two pieces of coloured cotton cloth as shown

State what is observed in each experiment (1mk)

Experiment I

______________________________________________________________________

Experiment II

______________________________________________________________________

Explain your observation using an equation (1mk)

______________________________________________________________________

a) what is meant by solubility? (1mk)

________________________________________________________________________

b) In an experiment to determine the solubility of solid Y in water at 30^oC the following results were obtained.

Mass of evaporating dish = 26.2g

Mass of evaporating dish + saturated solution = 42.4g

Mass of evaporating dish + dry solid y = 30.4g

Using the information, determine the solubility of solid Y at 30^oc in grams per 100g of water (2mks)

________________________________________________________________________

the molar heat of formation of carbon(ii) oxide is ^–105kjmol^-1, molar heat of combustion of carbon is -393 kjmol^-1

by using an energy cycle diagram, determine the molar heat of combustion of carbon(ii)oxide (3mks)

________________________________________________________________________

The diagram below was used to study the effect of heat on copper(ii)sulphate crystals

Name liquid M (1mk)

_____________________________________________________________________

State and explain the precaution that should be made before stopping heating (2mks)

_____________________________________________________________________

Deuterium ²₁D and tritium ³₁T are two isotopers of hydrogen. They react to form element Y and neutron particles according to the equation below.

²₁D + ³₁T ^a_bY + ¹₀n

Find the value of a and b (2mks)

________________________________________________________________________

What name is given to the type of reaction undergone by the isotope of hydrogen (1mk)

________________________________________________________________________

A gas occupies 4dm³ at -23⁰c and 152mmHg. At what pressure will its volume be halved, if the temperature then is 227⁰c? (2mks)

________________________________________________________________________

Ammonium nitrate was gently heated and the products collected as shown in the diagram

Identify
Colourless liquid H (1mk)

____________________________________________________

Gas G (1mk)
Describe one chemical test that can be used to identify gas G

_____________________________________________________________________

The diagram below shows the acidic and basic oxides fit into the general family of oxide

State the type of oxide that would be placed in the shaded area (1mk)

_____________________________________________________________________

Name an oxide that would be placed in the shaded area (1mk)

_____________________________________________________________________

A dynamic equilibrium between dichromate and chromate ions is established as shown in the equation below.

Cr₂O₇^2-(aq) + ZOH^–(aq) 2Cro^2-₄ + H₂O (l)

Orange Yellow

What is meant by dynamic equilibrium? (1mk)

_____________________________________________________________________

State and explain the observation made if a dilute hydrochloric acid is added to the equilibrium mixture (2mks)

_____________________________________________________________________

An experiment showed that the composition of a compound to be 5838% Barium, 13.72% Sulphur and 27.47% oxygen. Calculate the empirical formula of the compound (Ba = 137; S=32, O=16) (3mks)

________________________________________________________________________

In an experiment to study diffusion of gases, the following set up was used

State and explain observations made in the experiment (2mks)

________________________________________________________________________

Write an equation for the reaction that occurs in the experiment (1mks)

__________________________________________________________________

The figure below is an energy level diagram for the reaction 2Z (g) + 2B(g) = 2AB(g)

Explain the effect of yield AB by

Increase in pressure (1 ½ mk)

_____________________________________________________________________

Decrease in temperaline (1 ½ mk)

_____________________________________________________________________

Study the following changes that took place when the following substances are exposed to air.
NaOH(s) I NaOH(aq)

N₂CO₃.IOH₂O(s) II Na₂CO₃(s) + IOH₂O(l)

CuSO₄(s) + 5H₂O(l) III CuSO₄.5H₂O(s)

Name the process (3mks)

I _______________________________

II ______________________________

III _____________________________

A white solid K was heated. It produced a brown gas A and another gas B which relights a glowing splint. The residue left was yellow when hot and white when cold.
Identify gases A and B (2mks)

A ______________________________

B ______________________________

Write an equation for the decomposition of solid K (1mk)

_____________________________________________________________________

Bronze is an alloy of copper and another metal. Identify the other metal.

_______________________________________________________________________

MOCKS 1 2023

NAME…………………………..………………DATE ………………………………………

INDEX NO.……….……….………………………..… SIGNATURE ……………..………

233/2

CHEMISTRY

(THEORY)

PAPER 2

THEORY

The grid below shows part of the periodic table. Study it and answer the questions that follow. The letters do not represent the true symbols of the elements.


				A
I	B	C	D		E
F	G				H

Which element forms an ion of charge – 2? Explain your answer 2marks

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

(b) What is the nature of the oxide formed by element C? 1mark

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

How does the reactivity of H compare with that of E? Explain. 2marks

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

Write the chemical equation for the reaction between B and chlorine? 1mark

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

Explain how the atomic radii of the following compare; 2marks

F and G

B and G

The oxides of B and D are separately dissolved in water. State the effect of each product on litmus paper. 2marks

20cm³ of a solution of a hydroxide of I completely neutralizes 17.5cm³ of 0.5M sulphuric (VI) acid. Calculate the concentration in moles/litre of solution of the hydroxide of I3marks

a) Sulphur occurs naturally in two different forms called allotropes;

What are allotropes? 1mark

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

The two allotropes of sulphur are stable at different temperatures, as shown in the equation below.

Above 95.5⁰C

Rhombic sulphur Monoclinic sulphur

Below 95.5⁰C

Give a name to the temperature 95.5⁰C 1mark

…………………………………………………………………………………………………

b) Below is a flow chart diagram for the contact process for the manufacture of sulphuric (VI) acid.

Give the name of chambers labeled 1 ½ mark

………………………………………………………………

……………………………………………………………….

State the three conditions in the converter. 1 ½ mark

Explain why gases are passed through ; 2marks

I – The dust precipitator and drying power

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

II- The chamber labeled YWrite the balanced equations for the reactions in;3marks

Step 2:

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

Step 3:

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

Step 4:

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

Calculate the volume of sulphur (VI) oxide gas in litres that would be required to produce 178kg of Oleum in step 3. (Molar gas volume at s.t.p.=22.4l, H=1, O=16, S=32)3marks

Below is a scheme of some reactions of propanol. Study it and answer the questions that follow.

State the reagents and conditions required to effect step I 3marks

Draw the structural formulae and name product Z. 1mark

Name product Q 1mark

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

Explain how product Y can be distinguished from the product formed after step I has taken place. 2marks

What name is given to the process in Step II and step III 2marks

Step II

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

Step III

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

(i) Define the term hydrocarbon 1mark

(ii) Draw the structure of 1, 2 – dibromopropane 1mark

What is the molar heat of combustion of a substance? (1mark)

The experiment below was set up to determine the molar heat of combustion of methanol.

The following data was obtained from the above experiment.

Mass of burner + methanol before burning = 62.74g

Mass of burner + methanol after burning = 62.36gFinal temperature of water = 38.5⁰C

Initial temperature of water = 23.5⁰C

Volume of water used = 100cm³

From the above results work out the molar heat of combustion of methanol. (3marks)

(Density of water =1g/cm³, C = 12, O=16, H= 1.0)

Specific heat capacity of solution 4.2Kj K^-1_g K^-1)

Write a thermo chemical equation for this reaction. (1mark)

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

Explain why the value obtained in (i) above may be lower than the actual value. (1mark)

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

Study the data given below

C₃H_8(g) + 5O_2(g) 3CO_2(g) + 4H₂O_(l)ΔH = – 2209 KJmol^-1

H_2(g)+ ½ O_2(g) H₂O_(l)ΔH = -286KJmol^-1

C_(s) + O_2(g)CO_2(g)ΔH = -406KJmol^-1

Use this information to find the heat of formation of propane. (3marks)

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

What do you understand by the term heating value of a given fuel? (1mark)

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

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

State two factors you consider when choosing a fuel. (1mark)

…………………………………………………………………………………………………

Magnesium ribbon was reacted with steam as shown in the diagram below.

State two observations in the boiling tube. (2marks)

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

Describe how you test for gas x (2marks)

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

State one industrial use of the product formed in the boiling tube at the end of the experiment. (1mark)

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

- Explain what is meant by the term neutralisation. (1mark)

Starting with 50cm³ of 2M nitric (v) acid, describe how you would prepare crystals of sodium nitrate. (3marks)

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

Complete the table below. (1mark)

Indicator	Colour in
Indicator	Acidic solution	Alkaline solution
Phenolphthalein	__________	Pink
Methyl Orange	Pink	__________

When magnesium is burnt in air two reactions take place forming two different compounds. Write down the equations for the two reactions. (2marks )

The set up below is used to measure the change in mass during the course of the reaction between dilute hydrochloric acid (Excess) and marble chips at 22⁰C.

Changes in mass were noted at one minute intervals and were as follows;

Time (Min)	1	2	3	4	5	6	7
Loss in mass (g)	0.26	0.46	0.60	0.69	0.73	0.73	0.73

Write an equation for the reaction taking place in the flask. (1mark)

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

Give a reason why the mass of the flask charged with time? (1mark)

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

What is the role of cotton wool at the mouth of the flask? (1mark)

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

Explain why it is not advisable to use dilute sulphuric (VI) acid with marble chips in this experiment (1mark)

Plot a graph of loss in mass (vertical axis) against time. Label the curve 22⁰C (3marks)

On the same axis in (e) above sketch the graph you would expect to obtain if the experiment was repeated at 35⁰ Label the curve 35⁰C. (1mark)
State what would happen if the marble chips were replaced with the same mass of marble powder. Explain your answer. (1mark)

Determine the volume of carbon (IV) oxide produced if 0.12g of marble chips was reacted with excess dilute hydrochloric acid. (Experiment done at room temperature and pressure. Molar gas volume at r.t.p = 24dm³,Ca = 40.0,O = 16, C = 12.0) (2marks)

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

In an experiment ,0.71g of hydrated sodium carbonate (Na₂CO₃.XH₂O) was treated with dilute nitric v acid and the gas evolved was carbon iv oxide which was measured using a syringe at stp.The volume of carbon iv oxide obtained was 56cm³

a.Write the equation for the reaction between anhydrous sodium carbonate and dilute nitric v acid (1mk)

Calculate the number of moles of carbon iv oxide gas collected at s.t.p (molar gas volume at stp=22,400) (2mks)

c.Calculate the mass of anhydrous sodium carbonate reacted (3mks)

d.Calculate the mass of water in 0.715g of hydrated sodium carbonate (1mk)

Determine the R.F.M of hydrated sodium carbonate, hence the value of X(3mks)

MOCKS 1 2023

Name _________________________________________ Index No. _____________________________

Candidate’s Signature ___________________

Date _________________________________

233/3

CHEMISTRY

PAPER 3

PRACTICAL

2 ¼ HOURS

INSTRUCTIONS TO CANDIDATES

Write your name and admission number in the spaces provided.
Sign and write the date of examination in the spaces provided above.
Answer all questions in the spaces provided.
KNEC Mathematical tables and silent non-programmable electronic calculators may be used.
All working must be clearly shown where necessary.
Candidates should answer all the questions in English.

FOR EXAMINER’SUSE ONLY

Question	Maximum Score	Candidate’s Score
1	19
2	10
3	11
TOTAL SCORE	40

This paper consists of 8 printed pages

Turn Over

You are provided with:

– Solution A, a mixture of two bases sodium hydroxide and sodium carbonate solids

dissolved in a 1 litre solution.

– Solution B, 0.2M hydrochloric acid.

– Phenolphthalein and methylorange indicators.

– Solution C, barium chloride solution.

You are required to determine the concentration of each of the reactants in the mixture.

Procedure 1

Pipette 25.0cm³ of solution A into a conical flask.

Add two drops of methylorange indicator.

Titrate solution A with B until the yellow colour just changes to pink.

Record your results in the table below.

Repeat the procedure to obtain two more readings.

Table I (3 marks )

	1	2	3
Final burette reading (cm³)
Initial burette reading (cm³)
Volume of solution B used (cm³)

(a) Calculate the average volume (V₁) of solution B used. (1 mark )

(b) Calculate the number of moles of hydrochloric acid that reacted. (1 ½ marks )

Procedure II

Pipette 25.0cm³ of solution A into a conical flask. Measure 15.0cm³ of barium chloride

solution (solution C) with clean measuring cylinder.

Add it to the solution A in the conical flask. Shake it gently and add three drops of phenolphthalein indicator.

Titrate solution B into the conical flask until the pink colour just changes to colourless.

NB: The white precipitate should remain in the flask.

Repeat the procedure to obtain two more readings.

Table II ( 3 marks )

	1	2	3
Final burette readings (cm³
Initial burette reading (cm³)
Volume of solution B used (cm³)

(c ) Calculate the average volume (V₂) of solution B used. (1 mark )

(d) The equation for the formation of white precipitate

Na₂CO_{3 (aq)}+ BaCl_{2 (aq)} BaCO_{3 (s)}+ 2NaCl _(aq)

During titration II the white precipitate formed after adding barium chloride does

not take part in the titration but all the hydroxide ions (OH^–) in the solution are neutralized.

(i) Calculate the moles of the acid (solution B) reacting in titration II. ( 1 ½ marks )

(ii) Calculate moles of sodium hydroxide (OH^–) reacting during the titration. ( 1 ½ marks )

(e) Calculate number of moles of acid that reacted with sodium carbonate in the mixture. ( 1 ½ marks )

(f) Calculate the concentration of solution A in terms of sodium hydroxide in

moles per litre. ( 1 ½ marks )

(g) Write an ionic equation for the reaction of the acid with sodium carbonate. ( 1 mark)

(h) (i) Calculate the number of moles of sodium carbonate in the mixture. (1 mark )

(ii) Calculate concentration of solution A in terms of sodium carbonate in

moles per litre. (1 ½ marks )

You are provided with solid Z. Carry out the tests below and write your observations

and inferences.

(a) Using a clean metallic spatula, heat a half of solid Z in a Bunsen burner flame.

Observation

Inferences

( 1 ½ marks )

( 1 marks

(b) Dissolve the remaining portion of solid Z into 10cm³ of distilled water in a boiling tube.

Divide the resulting solution into four portions.

Observation

Inferences

( 1 mark )

( ½ mark )

(c ) To 1^st portion, add 3 drops of acidified potassium manganate (VII)

Observation

Inferences

( ½ mark )

( 1 ½ marks )

(d) To the 2^nd portion, add 3 drops of acidified potassium dichromate (VI) and warm.

Observation

Inferences

( ½ mark )

( 1 ½ marks )

(e) To the 3^rd portion, add all the NaHCO₃ provided.

Observation

Inferences

( 1 mark )

( ½ mark )

(f) To the 4^th portion, add 3 drops of universal indicator and determine the pH value.

Observation

Inferences

( 1mark )

( ½ mark )

You are provided with solid Y. Carry out the tests below and record your observations and

inferences in the spaces provided.

(a) Place half of solid Y in a boiling tube and heat. Test any gas produced with litmus paper.

Observation

Inferences

( 1 ½ marks )

( 1 mark )

(b) Place the remaining solid Y into a boiling tube. Add about 10cm³ distilled water and

shake. Divide the resulting solution into 5 portions.

Observation

Inferences

( ½ mark )

(c ) To the 1^st portion, add NaOH_(aq)dropwise till in excess.

Observation

Inferences

( 1mark )

( ½ mark )

(d) To the 2^nd portion, add NH_{3 (aq)}dropwise till in excess.

Observation

Inferences

( 1 mark )

( ½ mark )

(e) To the 3^rd portion, add 1cm³ of acidified hydrogen peroxide followed by

NaOH_(aq)dropwise till in excess.

Observation

Inferences

( 1 mark )

( ½ mark )

(f) To the 4^th portion, add 3 drops of lead (II) nitrate and then filter.

Observation

Inferences

( 1 mark )

(g) To the 5^th portion, add 3 drops of acidified barium nitrate solution.

Observation

Inferences

( ½ mark )

MOCKS 1 2023

233/3

CHEMISTRY

PAPER 3

PRACTICAL

021

Kenya Certificate of Secondary Education

CHEMISTRY

PAPER 3

CONFIDENTIAL TO SCHOOLS

The information contained in this paper is to enable the head of Institution and the teacher in charge of Chemistry to make adequate preparations for the Form 4 entrance examination. NO ONE ELSE should have access to this paper or acquire knowledge of its contents. The teacher in charge of Chemistry should NOT perform any of the experiments in the same room as the candidates NOR make the results of the experiments available to the candidates or given any other information related to the experiments to the candidates. Doing so will constitute an examination irregularity which is punishable.

In addition to the apparatus and fittings found in a Chemistry Laboratory, each candidate will require the following:

1g solid Y
1g solid Z
Metallic spatula
6 test tubes in a rack
2 boiling tubes
Test tube holder
Filter funnel
Filter paper (one)
Distilled water
Acidified potassium manganate (VII) + dropper
Acidified potassium dichromate (VI) + dropper.
About 1g of NaHCO_{3 (s)}
pH chart
Universal indicator.
2M NaOH_(aq)+ dropper
2M NH_{3 (aq)}+ dropper.
Blue and red litmus papers.
Acidified hydrogen peroxide + dropper.
Measuring cylinder (10 mls ).
Acidified 2M Barium Nitrate + dropper
2M Lead (II) nitrate + dropper.
Bunsen Burner.
150cm³ of solution A.
150cm³ of solution B
50cm³ of solution C
25.0cm³ pipette.
50.0cm³ burette.
A clamp and stand.
100ml measuring cylinder.
3 conical flasks.
White tile.
Phenolphthalein indicator.
Methyl orange indicator.

NOTE:

- Solution A is prepared by dissolving a mixture of 8g sodium hydroxide and 10.6g sodium carbonate in distilled water to make 1 litre solution.
- Solution B is prepared by measuring 17.2cm³ of concentrated hydrochloric acid ( specific gravity 1.18) to 500cm³ of distilled water and then making it to one litre.
- Solution C 0.1M barium chloride solution.
- Solid Y – Hydrated ammonium iron (II) sulphate
- Solid Z – Maleic acid

MOCKS 1 2023

MARKING SCHEME

233/2

CHEMISTRY

PAPER 2

JULY/AUGUST

Question 1

A (√1mk) elements in group (vi) have 6 electrons in the outermost energy level, they react by gaining 2 electrons.√1mk
Amphoteric Oxide √1mk
Element E is more reactive than H (√1mk) Elements E and H are non – metals in group (VII) and reactivity decreases down the group √1mk / E is smaller than H and hence has a higher electron affinity therefore more reactive.
B_(s) + Cl_2(g) BCl_2(s) 1mk
(i) The atomic radius of element F is greater than that of G √1mk / Across period number of protons (nuclear charge increases increasing effective nuclear charge.

(ii) The atomic radius of element G is greater than that of B. √1mk

Solution of oxide of B changes red litmus paper blue and has no effect on blue litmus paper 1mk while solution of oxide of D changes blue litmus paper red and has no effect on red litmus paper. 1mk
2IOH (aq) + H₂SO₄ (aq) I₂SO₄(aq) + 2H₂O(l) √1mk

2 : 1

Moles of H₂SO₄17.5 x0.5 = 0.00875moles √½ mk

1000

Moles of IOH 0.00875 ÷ 2 = 0.004375 moles √½ mk

Molarity of IOH = 1,000 x 0.004375

= 0.21875M √1mk

Concentration = 0.21875 moles/litre √½ mk

Question 2

(i) Crystalline forms of sulphur √1mk

Existence of sulphur in more than one form in the same physical state.√1mk

(ii) Transition temperature √1mk

(i) X – dilution chamber √1 ½ mk

Y- Heat exchanger √1 ½ mk

Z – Burner √1 ½ mk

(ii) Vandalism (v) catalyst √1 ½ mk

Temperature – 500⁰C √1 ½ mk

Pressure – 200atm √1 ½ mk

I – To remove dust particles and water vapour that could otherwise poison the catalyst √1mk

II- Lose heat and pre-heat incoming gases √1mk

Step 2; 2SO_2(g) + O_2(g) 2SO_3(g) √1mk

Step 3: SO_3(g) + H₂SO_4(l) H₂S₂O_{7 (l)} √1mk

Step 4: H₂S₂O_7(l) + H₂O_(l) 2 H₂SO_4(l) √1mk

H₂SO_4(l) + SO_3(g) H₂S₂O_7(l) √½ mk

1 : 1 : 1

1 mole of oleum = 178,000 = 1,000moles

178

1 mole at s.t.p = 22.4L

1,000moles = ? √½ mk

= 1000 x 22.4 = 22,400 litres √1mk

Question 3

Reagent : Hydrogen gas √1mk

Conditions: – Nickel catalyst √1mk

– I50-250⁰C (temperature) √1mk

H H H

H C C C H

Br H H

I – Bromopropane √1mk

Polypropene √1mk
Y decolourisesbromine water √1mk while the product formed after step I has taken place does not √1mk
Step II – dehydration √1mk

Step III – substitution √1mk

(i) A hydrocarbon is a compound that contains carbon and hydrogen only √1mk

(ii) H H H

H C C C H

Br Br H √1mk

Question 4

Molar heat of combustion is the enthalpy change that occurs when one mole of a substance is burnt completely in oxygen. ^{√ 1 mk}
1. Mass of methanol = 0.38g ^{√ ½ mk}

Change in temp. ΔT = 38.5 – 23.5

= 15⁰C

Heat produced. = MCDT

= 100 x 4.2 x 15 ^{√ ½ mk}

1000

= 63.1KJ.

Molar mass of ethanol (CH₃OH) = 32 ^{√ ½ mk}

Molar heat of combustion = 63.1 x 32 ^{√ ½ mk}

0.38

= 5313.68 KJ mol^-1

CH₃OH_(l) + H₂O_2(g) CO_2(g)+ 2H₂O_(l)^{√ 1 mk} ΔH = -5313.68KJmol^-1

Heat is lost to the environment

Hence the value is lower ^{√ 1 mk}

Equation for formation of propane.

3C_(s) + 4H_2(g) C₃H_8(g)^{√ 1 mk}

Heat of formation = 3 (-406) + 4 (-286) + 2209) ^{√ 1 mk}

= -1218 – 4576

= – 3585 KJmol^{-1 √ 1 mk}

This is the amount of heat energy given out when a unit mass or unit volume of fuel is completely burned in oxygen. ^{√ 1 mk}

Heating value
Ease and rate of combustion
Availability
Ease of transportation any 2 correct ½ mk each
Ease of storage
Environmental effects
Cost

Question 5

1. Magnesium burns with a bright white flame ^{√ 1 mk}

A white solid is formed ^{√ 1 mk}

Place a burning splint ^{√ 1 mk} near the mouth of the test tube containing the gas.

A ‘pop’ sound is produced.

This confirms that the gas is hydrogen ^{√ ½ mk}

Making lining of furnaces. ^{√ 1 mk}

1. This the reaction between a givennumber of moles of hydrogen ions (H⁺)^{√ 1 mk} and an equal number of hydroxide (OH^–) ions to form water.
2. Add 50cm³ of 2M^{√ 1 mk} sodium hydroxide solution.

Evaporate ^{√ ½ mk} the mixture to obtain a saturated solution.

Leave the saturated solution for some time to ^{√ ½ mk}
Filter the crystals and dry then dry then^{√ ½ mk} between two filter papers.

Indicator	Colour in
Indicator	Acidic solution	Alkaline solution
Phenolphthalein	Colourless ^{√ ½ mk}
Methyl Orange		Yellow ^{√ ½ mk}

2Mg_(s)+ O_2(g) 2MgO_(s)^{√ 1 mk}

3Mg_(s) + N_2(g) Mg₃N_2(s)^{√ 1 mk}

Question 6

CaCO_{3(s) +}2HCl_(aq) CaCl_2(aq) + H₂O_(l)+ Co_2(g)^{√ 1 mk}
The carbon (iv) oxide formed escaped into the atmosphere. ^{√ 1 mk}
To prevent acid from spraying out. ^{√ 1 mk}
Forms insoluble salt ^{√ ½ mk} of calcium sulphate which forms a coat ^{√ ½ mk} on the surface of the marble chips preventing any further reaction. ^{√ 1 mk}
The reactions rate would increase ^{√ ½ mk} marble powder provides a larger surface area, more particles are involved in reactions, thus increasing the rate of reaction. ^{√ ½ mk}
CaCo_3(s) + 2HCl+(aq)CaCl_2(aq) + H₂O_(l) + CO_2(g)^{√ ½ mk}

1mole 2moles 1mole

0.12g 0.12 x 24dm^{3√ 1 mk}

100

= 0.0288dm^{3 √ ½ mk}

Question 7

7(a) Na₂CO₃(s) + 2HNO₃(aq) 2NaNO₃(aq) + CO₂(g) +H₂O(l)

(b) 1 mole of CO₂(g) 22400cm³

56cm³

=0.0025 moles

1 : 1

? 0.0025moles

0.0025moles of Na₂CO₃

1Mole of Na₂CO₃= 106g

0.0025moles = ?

= = 0.265g

(d) Mass of water= 0.715-0.265=0.45g

(e)

	N_a2CO₃	H₂O
Mass	0.265g	0.45g
RFM	106	18
Moles	0.265/106=0.0025	0.45/18=0.025
Mole ratio	0.0025/0.0025=1	0.025/0.0025=10

X=10

233/3

CHEMISTRY

PAPER 3

PRACTICAL

021

Kenya Certificate of Secondary Education

CHEMISTRY

PAPER 3

MOCKS 1 2023

MARKING SCHEME

Procedure I

Table 1

	1	2	3
Final burette reading	25.1	35.0	39.9
Initial burette reading	0.0	10.0	15.0
Volume of solution B used	25.1	25.0	24.9

( Compare / use the teacher’s value )

Award marks as follows:

A: Complete table ( 1 mark )

Conditions

Complete table with three titration 1 mark

Incomplete table with two titrations ½ ark

Incomplete table with one titration 0 mark

B: Decimal place ( 1 mark)

Conditions :

Accept only one or two decimal places used consistently.

If two decimal place the 2^nd decimal place MUST be either o or 0.5

C : Accuracy 1 mark

Compare the student’s titre value with teacherstitre values.

Conditions

At least within ± 0.1 1 mark

At least within ± 0.2 ½ mark

Above ± 0.2 0 mark

D: Principles of averaging 1 mark

Values averaged must be shown and within ± 0.1 of each other

(a) 25.1 + 25.0 + 24.9 Ö ½

= 25.0cm³Ö ½

(b) Moles of acid that reacted

If 1000cm³ 0.2 moles

Then 25cm³ 25.0 x 0.2 Ö1

1000

= 0.005 moles Ö ½

Procedure II

Table II

Award according to procedure I table I

	1	2	3
Final burette reading	12.6	25.1	37.6
Initial burette reading	0.0	12.6	25.1
Volume of solution B used	12.6	12.5	12.5

( Compare / use the teacher’s value )

(c ) 12.6 + 12.5 + 12.5 Ö ½

= 12.5333cm³Ö ½

(d) (i) Moles of the acid

If 1000cm³ 0.2 moles

12.5333cm³ 0.2 x 12.5333 Ö1

1000

= 0.002506 moles Ö ½

(ii) Moles of sodium hydroxide

Mole ratio

H⁺ :OH^–

1 : 1 Ö1

\0.002506 : 0.002506

Ie 0.002506 moles Ö ½

(e) Moles of acid that reacted with sodium carbonate

Ans (b) – ans (dii)

0.005 moles – 0.002506 moles Ö1

= 0.002494 moles Ö ½

(f) Molarity of A in terms of NaOH

If 25.0cm³ 0.002506

The 1000cm³ 0.002506 x 1000 Ö1

25cm³

= 0.10024M Ö ½

(g) CO₃^2-_(aq)+ 2H⁺_(aq) H₂O _(l)+ CO_{2 (g)}

[Unbalanced 0 mark

Missing state symbol ½ mark]

(h) (i) Moles of sodium carbonate

½ x 0.002494 Ö ½

= 0.001247 moles Ö ½

(ii) Molarity of A in terms of Na₂CO₃

If 25cm³ 0.001247

Then 1000cm³ 0.001247 x 1000 Ö1

= 0.04988M Ö ½

	Observations	Inferences
2. (a)	– Solid melts Ö ½ – Burns in yellowÖ ½ sooty flame Ö ½ Max 1 ½ marks	– Presence of either C = C Ö ½ or C CÖ Max 1 mark
(b)	– Dissolves Ö ½ into a colourless Ö ½ solution Max 1 mark	– Solid is polar Ö ½ Max ½ mark
(c )	– Acidified KMnO₄changes from purple to colourless Ö ½ Max ½ mark	– Presence of either C CÖ ½ or C CÖ ½ or R – OH Ö ½ Max 1 ½ marks
(d)	– Acidified K₂Cr₂O₇ changes from orange to green Ö ½ Max ½ mark	– Presence of either C CÖ ½ ; C CÖ ½ or R – OH Ö ½ Max 1 ½ marks
(e)	– EffervencesÖ ½ production of colourless gas Ö ½ Max 1 mark	H⁺Ö ½ / O C OH present Max ½ mark
(f)	pH 4 Ö ½ Max ½ mark	Weakly acidic Ö ½ Max ½ mark

3 (a)	– Colourless liquid on cooler parts of test tube Ö ½ – Colourless gas with pungent smell Ö ½ – Gas turns moist red litmus blue Ö ½ / Blue litmus remains blue Ö ½	– Hydrated salt Ö ½ – Presence of NH₄⁺Ö ½ 1
(b)	– Solid dissolves into pale green solution Ö ½ – 1	– Polar solid Ö ½ – Presence of Fe²⁺Ö ½ 1
(c )	-Green Ö ½ ppt insoluble Ö ½ in excess – PPt turns brown on exposure to air Ö ½ 1 ½	– Presence of Fe²⁺Ö ½ – Fe²⁺ oxidized to Fe³⁺ by air Ö 1 1

(d)	– Green ppt Ö ½ insoluble in excess – Ppt turns brown on exposure to air Ö ½ 1 ½	– Presence of Fe²⁺Ö ½ – Fe²⁺ oxidized to Fe³⁺ by air Ö ½ 1
(e)	– Pale green solution turns yellow Ö ½ – Brown Ö ½ ppt insoluble Ö ½ in excess 1 ½	– Presence of Fe³⁺Ö ½ ½
(f)	– Formation of white ppt Ö ½ as residue and green solution as filtrate Ö ½ 1	– Presence of Fe²⁺Ö ½ – Presence of either Ce^–Ö ½ , SO₄^2-Ö ½ or SO₃^2-Ö ½ , CO₃^2-Ö ½ Max 2 marks
(g)	– White ppt forms Ö ½ ½	SO₄^2- present Ö ½ ½

MOCKS 1 2023

MARKING SCHEME

233/1

CHEMISTRY

PAPER 1

THEORY

(a) K 2. 8.8.2 √1mk

M 2.6 √1mk

(b) K ²⁺

M ^2-

2 (a) Anode: I^– (l) I₂ (g) +2e^–√1mk

Cathode: Pb²⁺+ 2e^– Pb (s)√1mk

b) Increase in temperature increases the kinetic energy (1/2 mrk) of positive centres and electrons making them to vibrate more. These increase collisions of positive centres and electrons hence increased resistance (1/2mrk)
Add water to the mixture and stir sodium chloride dissolve leaving copper (ii) oxide which is insoluble. (√1mk)

Filter(1/2) to remove copper (ii) oxide and sodium chloride as the filtrate

Evaporate the filtrate to saturation and cool to obtain sodium crystals (√1mk)

Dry them between filter papers/leave them in the open to dry (√1mk)

Hot platinum wire glows red. (√1mk)

Brown fumes are observed (√1mk)

Reaction between oxygen gas and ammonia gas over platinum wire is exothermic. (1/2mrk)

Ammonia is oxidized to nitrogen (ii) oxide which reacts with excess oxygen to form nitrogen (iv) oxide,(1/2 mrk)

a) A bond formed by two atoms/elements by share of electrons from one of the atoms/element(√1mk)

a) Remove / absorb carbon (iV) oxide (√1mk)

b) 3Mg (s) + N₂(g) Mg₃N₂ (s) (√1mk)
c) Neon/ Argon (√1mk)
a) But – 1 – ene (√1mk)
b) Pent – 2 –ene (√1mk)
c) Potassium manganate (VII) is decolourised/ Potassium manganate (VII) changes colour from purple to colourless (√1mk)

a) The outer zone has complete combustion and hence hotter tha the middle zone forming the charred black part (1mrk) Middle zone has incomplete combustion and hence less hot forming unburnt part (√1mk)
b) – Non – luminous flame is hotter than luminous flame (1mrk)

Non – luminous flame does not produce soot (1mrk) Any one (√1mk)

a) Sulphuric (VI) acid react with marble (Calcium carbonate) forming insoluble calcium sulphate(1mrk) which form a coat over marble stopping any further reaction (√1mk)
b) Oil is less dense (1/2) than water making oil float(1/2) on top hence continues to burn.
2XOH(aq) + H2SO4(aq) X2SO4 (aq) + 2 H2O(l)

XOH = 2 = 15 X M

H2SO4 1 20 X 0.045 (√1mk)

M = 2 X 20 X 0.045

1 X 15 = 0,12 moles/l (1/2)

1mole = 2.88

0.12 = 24 (1/2)

RFM of XOH = X + 16 + 1 (1/2)

X = 7 1/2)

a) 2CxHy X CO2 + y/2 H2O

X = 6

2 = 3 (1/2)

Y = 12

3 = 6 (1/2)

MF = C3H6 (1/2)

Structural fprmula = CH3 CH = CH2 (1/2)

b) Alkenes
on the diagram
a) √1mk
b) arrow from zinc half-cell towards copper half cell √1mk
c) Zn(s) + Cu²⁺(aq) Zn²⁺(aq) + Cu(s) √1mk

(i) Froath floatation √1mk

(ii) Concetrating the mineral ore by making impurities to sink atb the bottom. √1mk

(a) Exp. 1 – The colour of dry cloth did not turn to white/ cloth not bleached, because of the absence of hypochloric (I) acid which is responsible for bleaching

(b) Exp 2 – Wet cloth turned white due to bleaching as chlorine dissolves in water to form hypochloric(I) acid√1mk

b) Cl2(g) + H2O(g) + Dye {Dye + [O]} + 2HCl(g) √1mk

(a) Solubility is the maximum mass in grams of solute that will dissolve in 100g ofvwater at a given temperature/ is the mass in grams of solute required to make a saturated solution with 100g of water at given temperature. √1mk/

(b) Mass of solid Y = 30.4 – 26.2

= 4.2g (1/2mrk)

Mass of water in the solution = 42.4 – 30.4

= 12g (1/2 mrk)

12 g of water dissolve 4.2g solid Y

100g of ware will dissolve 100 x 4.2 (1/2mrk)

= 35g / 100g of water (1/2mrk)

AH⁰f(CO) + AH⁰c(CO) = AH⁰c(C)

-105 + AH⁰c(CO) = -393 √1mk

AH⁰c(CO) = -393 + 105 √1mk

= -188kJMol^-1 √1mk

a) Water √1mk

b)The delivery tube should first be removed √1mk to avoid sucking back of liquid M √1mk

a) Atomic mass of Y 2 + 3 = a + 1

a = 4 √1mk

Atomic number 1 + 1 = b + 0

b = 2 √1mk

b) Nuclear fusion √1mk)

V1 = 4dm3 ; P1 = 152mmHg ; V2 = 2dm3 ; T1 = 250K ; T2 = 500K P2 = ?

152 x 4 = P2 x 2

250 500 √1mk

P2 = 152 x4 x 500

250 x 2 √1mk

= 608mmHg √1mk

a) (i) Liquid H is Water √1mk

(ii) Gas G is Nitrogen (i) oxide √1mk

b) turn white anhydrous copper (II) sulphate to blue / Turns blue cobalt(II) chloride to pink √1mk
a) Amphoteric oxide √1mk
b) Lead (II) oxide / Zinc oxide / Aluminium (III) oxide (Any one) √1mk

a) Rate of forward reaction equals to the rate of backward reaction. √1mk
b) Orange colour of the solution intensifies √1mk

Equilibrium shift to the left/ backward reaction is favoured to replace OH^– that react with H⁺ √1mk

Element Ba S O

% composition 58.81 13.72 24.47

RAM 13732 16

No. of moles 58.81 13.72 24.47 (1/2mrk)

137 32 16

0.4293 0.4281 1.768

Mole ratio 1 1 4 (1/2mrk)

E . F. BaSO₄(√1mk)

(i) A white ring/ solid (1/2mrk) was formed inside the combustion tube closer to the cotton wool soaked in concentrated hydrochloric acid (1/2mrk). Ammonia is lighter/less dense than hydrochloric acid hence diffuse faster (√1mk)

(ii) NH₃ (g) + HCl(g) NH₄Cl(s) (√1mk)

(i) The yield of AB is increased. (√1mk)

The forward reaction is accompanied by a decrease in volume(1/2mrk). Equilibrium shifts to the right following increase of the forward reaction (1/2mrk)

(ii) The yield of AB is increased’ (√1mk)

The forward reaction is exothermic.(1/2mrk) Decrease in temperature favours the forward reaction, equilibrium shifts to the right.(1/2mrk)

(a) Deliquescence (√1mk)

(b) Efflorescence (√1mk)

a) A – Nitrogen (IV) oxide/ NO₂(√1mk)

B – Oxgygen/ O₂(√1mk)

b) 2ZnNO₃ (g)2ZnO(s) + 4 NO₂(g) + O₂(g) (√1mk)
Tin (√1mk)

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