Kenya Certificate of Secondary Education 2020

233/2 - Chemistry - Paper 2

(Theory)
Trial 1 2020 Time- 2 Hours
Name ………………………………………… Index Number……………………/………………..

Signature ……………………………….. Date …………………/…….………/…………

INSTRUCTIONS TO CANDIDATES
1. Write your name and index no in the spaces provided above.
2. Sign and write the date of exam in the spaces provided above.
3. Answer all the questions in the spaces provided after each.
4. Mathematical tables and silent electronic calculators may be used.
5. All working must be clearly shown where necessary.
6. This paper consists of 12 printed pages. Candidates should check to ensure that all pages are printed as
indicated and that no questions are missing.
7. All answers should be written in English.

FOR EXAMINER’S USE ONLY

Question Maximum score Candidate’s score

1 10
2 14
3 10
4 10
5 12
6 13
7 11
Total 80

T1ch 2020 Turn over

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 Answer al questions in the spaces provided

1. (a)The table below shows the ions of elements W, X, Y, Z and their electron arrangement.
The letters do not represent the actual symbols of the element.
Ion Electron configuration
W- 2,8,8
X2+ 2,8,8
Y3+ 2,8
Z2- 2,8

(i) Which two elements belong to the same period? Give a reason. (2mks)
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(ii) In which group of the periodic table does Y belong? (1mk)
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(iii) Write the formula of the compound formed between W and X (1mk)
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(iv) What type of bond is formed between W and X. Explain. (2mks)
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(b) (i) What is a coordinate bond. (1mk)
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 (ii) Draw a dot (.) cross (X) diagram to show bonding in the Ammonium ion. NH4+ ion (N =

7, H = 1) (2mks)

c) Aluminum chloride and sodium chloride are both chlorides of period 3 elements.
Use this information to explain the following observations.
I A solution of A1CI3 in water turns blue litmus paper red while that of sodium chloride
does hot. (1 ½ mks)
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II The melting point of sodium chloride (801°C) is higher than that of A1C13 (180°C).
( 1 ½ mks)
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2. . (a) Give the names of the following compounds.
(i) CH3CH2CH2CH3 . (1 mk)
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(ii) CH3CHCHCH2CH3 (1 mk)
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(b) Study the information in the table below ad answer the questions that follow.

No. of carbon atoms per molecule Relative molecular mass of hydrogen

2 28

3 42

4 56

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 (i) Write the general formula of the hydrocarbons in the table. (1 mk)
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(ii) Predict the relative molecular mass of the hydrocarbon with 5 carbon atoms. (1mk)
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(iii) Determine the molecular formula of the hydrocarbon in (ii) and draw its structural
formula. (2 mks)
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(c) Study the scheme given below and answer questions that follow.

(i) Name the reagent used in

Step I (1 mk)
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Step II (1 mk)
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Step III (1 mk)
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(ii) Write an equation for complete combustion of CH  CH (1 mk)
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(iii) Explain one disadvantage of the continued use of items in step III. (1 mk)
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3. Air was passed through several reagents as shown in the flow chart below.

(a) Name the major components of air. (2mks)

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(b) Write an equation for the reaction which takes place in the chamber with:
(i) Concentrated sodium hydroxide. (lmk)

(ii) Excess heated copper turnings. (lmk)

(iii) Excess heated magnesium powder. (1mk)

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 (c) Name one gas which escapes from the chamber containing magnesium powder. Give a reason
for your answer. (2mks)
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(d) Name the substance that was eliminated by electrostatic precipitation. (lmk)
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(e) Name a reagent that can be used in place of concentrated sodium hydroxide. (1 mk)
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(f) Name substance C. (lmk)

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(g) State three uses of gas C. (3mks)
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4. (a) Study the flow chart below and answer the questions that follow.

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Residue V was yellow when hot and white when cold.
(i) Identify
I White precipitate I. (1mk)
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II Solution II. (1mk)
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III Residue V. (1mk)
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(ii) Write an ionic equation for the reaction of solution II with Pb(NO3)2(aq). (1 mk)
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(iii) Write observations that would be made when ammonia solution is added drop wise
till in excess to the colourless solution II (lmk)
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(b) The diagram below represents a set-up for large scale manufacture of hydrochloric acid.
Study it and answer the questions that follow:

(i) Name substance X. (1 mk)

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 (ii) What is the purpose of glass beads? (1 mk)
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(iii) Give one source of substance X used in the above process. (lmk)
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(iv) Give two use of hydrochloric acid. (2mks)
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(c) The table below shows the ammeter readings obtained when two different electrolytes of the same
concentration were tested.

Electrolyte Ammeter reading (Amps)

Hydrochloric acid 4.0

Ethanoic acid 1.2

Why does Ethanoic acid give a lower ammeter reading? Explain your answer (2mks)
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5. The set-up below was used to prepare and collect gas X. During the experiment cleaned magnesium
ribbon was strongly heated before heating the wet glass wool.

(a) Name gas X ………………………………………………………………… (1mk)

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(b) Why is magnesium ribbon cleaned before it is used? (1mk)
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(c) State one observation that would be noted in the reaction tube. (1mk)
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(d) Write the equation for the reaction in the reaction tube. (1mk)
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(e) State one industrial use of the solid product formed in the reaction tube. (1mk)
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(f) What precaution should be taken at the end of experiment? Explain. (2mks)
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(g) At the end of the experiment 96.0cm3 of gas X were collected at 100C and 1 atmosphere
pressure. Mg = 24, M.G.V = 22.4, T = O0c AT STP, p = 1 atmospere at stp).
(i) Determine the volume gas X would occupy at s.t.p? (2mks)
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(ii) Calculate the mass of magnesium ribbon used Mg = 24. (2 mks)

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6. The flow chart below shows the large-scale manufacture of nitric (V) acid. Study it and answer the
questions below.

(a) Name substance X. (1mk)

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(b) Identify one source of X in this process. (1mk)
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(c) Write a balanced equation for the reaction which take place.
(i) At Step II. (1mk)
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(ii) In the absorption tower. (1mk)
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(d) Name the catalyst used in this process. (1mk)
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(e) Why is it not advisable to store nitric (V) acid in a transparent bottle? (1 mk)
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 (f) The apparatus below was arranged to investigate the properties of nitric (V) acid. Study the set-
up and answer the questions that follow:

(i) Explain what would be observed when blue and red litmus paper is dropped into flask Y
after the experiment. (2 marks)
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(ii) Write an equation for the reaction in test tube X above. (1 mark)
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(iii) What gaseous products would be expected if concentrated sulphuric (VI) acid was used
in place of conc. nitric (V) acid? (1 mark)
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7. (a) Explain the following observation, giving an equation where necessary. When a
sample of tap water is boiled for some time, a white precipitate is formed. (lmk)
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(b) A sample of hard water is found to contain 0.25g of calcium chloride and 0.24g of magnesium
sulphate per litre.
(i) Describe how this sample of water is softened by using anhydrous sodium
carbonate (2mks)
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 (ii) Calculate the mass of anhydrous sodium carbonate required to soften a litre of the
water sample (Ca= 40, Mg = 24, Na = 23, 0 = 16, Cl = 35.5, S = 32 and C = 12)
(3mks)
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(iii) Give two reasons why it is necessary / important to soften tap water supplied for
domestic . (2mks)
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(c) Study the flow chart below and answer the questions that follow.

(i) Identify solid T (lmk)

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(ii) Write an equation for the reaction between solid T and concentrated nitric (v) acid.
(lmk)
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(iii) Write an equation for the reaction that produces solution Q. (lmk)
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