Chemistry Paper 1 Questions and Answers - KCSE 2022 Mock Exams Set 1

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INSTRUCTIONS TO CANDIDATES

Write your Name, Index Number and School in the spaces provided above
Answer all the questions in the spaces provided after each question
KNEC Mathematical tables and silent non-programmable electronic calculators may be used
ALL working must be clearly shown where necessary
Candidate should check the question paper to ascertain that all the pages are printed and that no questions are missing
Candidates should answer the questions in English

FOR EXAMINER’S USE ONLY

QUESTIONS	MAX SCORE	CANDIDATE’S SCORE
1 – 29	80

QUESTIONS

1. Give the name of the ﬁrst member of the alkyne homologous series (1 mark)
2. Describe a chemical test that can be used to distinguish ethanol from ethanoic acid (2 marks)
1. Name the raw material from which aluminium is extracted (1 mark)
2. Give a reason why aluminium is extracted using electrolysis (1 mark)
3. Give one use of aluminium metal (1 mark)
1. What is meant by lattice energy? (1 mark)
2. Study the energy level diagram below and answer the question that follows:
  
  What type of reaction is represented by the diagram? (1 mark)
1. Sketch a graphical representation of Boyles law on the axes below (1 mark)
2. A gas occupies 400 cm³ at 25°C and 100,000 Pa What will be its volume at 27°C and 101325 Pa? (2 marks)
1. What is half- life? (1 mark)
2. The half-life of protactinium - 234 is 117 minutes Determine the mass that decays in 585 minutes starting with 100 g of the sample (2 marks)
State two disadvantages of hard water (2 marks)
Hydrogen chloride gas can be prepared by reacting sodium chloride with an acid
1. Name the acid (1 mark)
2. Write an equation for the reaction between sodium chloride and the acid (1 mark)
3. State two uses of hydrogen chloride (1 mark)
When solid B was heated strongly, it gave off water and a solid residue When water was added to the solid residue, the original solid B, was formed
1. What name is given to the process described? (1 mark)
2. Give one example of solid A (1 mark)
The set up below can be used to prepare oxygen gas Study it and answer the questions that follow
1. Identify X (1 mark)
2. Write the equation for the reaction which occurs in the flask (1 mark)
3. State one use of oxygen other than in welding (1 mark)
The atomic number of an element, M is 13
1. Write the electronic conﬁguration of the ion M³⁺ (1 mark)
2. Write the formula of the chloride of M (1 mark)
3. State the structure of the compound formed in (b) above (1 mark)
Concentrated sodium chloride was electrolysed using graphite electrodes Name the product formed at the anode and give a reason for your answer (2 marks)
The curve shown below shows the variation of time against temperature for the reaction between sodium thiosulphate and hydrochloric acid
1. Explain the shape of the curve (2 marks)
2. Other than temperature name one factor that affects the rate of reaction (1 mark)
1. Dry ammonia was passed over heated copper (II) oxide in a combustion tube
  1. State the observations made in the tube (1 mark)
  2. Write an equation for the reaction that occurs (1 mark)
2. What products would be formed if red hot platinum is introduced into a mixture of ammonia and oxygen? (1 mark)

The table below shows behaviour of metals P, Q, R and S Study it and answer the questions that follow:

Metal	Appearance on exposure to air	Reaction with water	Reaction with dilute sulphuric (VI) acid
P	Remains the same	Doesn’t react	Reacts moderately
Q	Remains the same	No reaction	Doesn’t react
R	Slowly tarnishes	Slow	Vigorous
S	Slowly turns white	Vigorous	Violent

Arrange the metals in the order of reactivity starting with the most reactive (2 marks)
Name a metal which is likely to be R (1 mark)

Given the following substances: sodium carbonate, orange juice and sodium bromide
1. Name one commercial indicator that can be used to show whether sodium carbonate, orange juice and sodium bromide are acidic, basic or neutral (1 mark)
2. Classify the substances in 15 (a) above as acids, bases or neutral (2 marks)
  
  Acid
  
  Base
  
  Neutral
The ﬂow chart below shows various reactions of zinc metal Study it and answer the questions that follow:
1. 1. Other than water, name another reagent that could be Q (1 mark)
  2. Write the formula of reagent P (1 mark)
2. Write an equation for the reaction in step 4 (1 mark)
1. One of the allotropes of sulphur is monoclinic sulphur, name the other allotrope (1 mark)
2. Concentrated sulphuric (VI) acid reacts with copper and prapanol State the property of the acid shown in each case (2 marks)
  Copper
  Propanol

Study the standard electrode potentials in the table below and answer the questions that follow

Half -reaction	E ^θ(V)
Ag⁺(aq) + e → Ag(s)	+ 0.80
Cu²⁺(aq) + 2e → Cu(s)	+ 0.34
Mg²⁺(aq) + 2e → Mg(s)	- 2.38
Ca²⁺(aq) + 2e → Ca(s)	- 2.87

Which of the metals is the strongest oxidising agent? (1 mark)
What observations will be made if a copper coin was dropped into an aqueous solution of calcium nitrate? Explain (2 marks)

Calculate the number of sulphate ions present in 225 cm3 of 2 M aluminium sulphate solution (L=60 × 1023) (3 marks)
1. A crystal of iodine, heated gently in a test tube gave off a purple vapour
  1. Write the formula of the substance responsible for the purple vapour (1 mark)
  2. What type of bond is broken when the iodine crystal is heated gently? (1 mark)
2. State one use of chlorine (1 mark)
Describe how samples of barium (II) sulphate, ammonium chloride and common salt can be obtained from a mixture of the three (3 marks)
1. Give the name of the process which takes places place when maize flour is converted to ethanol (1 mark)
2. Write the formula of the compound formed when ethanol reacts with sodium metal (1 mark)
1. Study the graph below which shows variation of atomic radius with atomic number
  
  State and explain the trend shown in the graph above (2 marks)
2. State one use of sodium (l mark)
A farmer intended to plant blueberries in her farm She first tested the pH of the soil and found it to be 100 In order to obtain high yield, what advice would be given to the farmer if blueberries do well in acidic solution? (2 marks)
Starting with calcium nitrate solution, describe how a pure dry sample of calcium carbonate can be prepared in the laboratory (3 marks)
A hydrocarbon contains 8182% of carbon If the molar mass of the hydrocarbon is 44, determine the molecular formula of the hydrocarbon (C = 120; H = 10) (3 marks)
1. Describe how Carbon (II) Oxide can be distinguished from Carbon (IV) Oxide using calcium hydroxide solution (2 marks)
2. What is the role of carbon (IV) oxide in ﬁre extinguishing? (l mark)
1. Name one source of alkanes (1 mark)
2. Methane gas was reacted with one mole of chlorine gas State the condition necessary for this reaction (1 mark)
1. What is meant by heating value of a fuel? (1 mark)
2. Other than heating value, name one factor to be considered when choosing a fuel (1 mark)

MARKING SCHEME

1. Give the name of the ﬁrst member of the alkyne homologous series (1 mark)
  Ethyne
2. Describe a chemical test that can be used to distinguish ethanol from ethanoic acid (2 marks)
  Put ethanol and ethanoic acid into separate test tubes. Add two drops of orange acidified potassium dichromate (VI) into each of the test tube. The acidified potassium dichromate (VI) will change to green in the test tube with ethanol and remain orange in test tube with ethanoic acid.
1. Name the raw material from which aluminium is extracted (1 mark) Bauxite
2. Give a reason why aluminium is extracted using electrolysis (1 mark) It is highly reactive
3. Give one use of aluminium metal (1 mark) Used to make airplane parts
1. What is meant by lattice energy? (1 mark)
  The energy change that occurs when an ionic substance is formed from its constituent ions in the gaseous state.
2. Study the energy level diagram below and answer the question that follows:
  
  What type of reaction is represented by the diagram? (1 mark)
  Exothermic
1. Sketch a graphical representation of Boyles law on the axes below (1 mark)
2. A gas occupies 400 cm³ at 25°C and 100,000 Pa What will be its volume at 27°C and 101325 Pa? (2 marks)
  P1V1 = P2V2
  T1 T2
  25º C=> 273 x 25 = 298 k
  27º C=> 273 x 27 = 300 k
  100,000 x 400 = 101325 x v2
  298 300
  v2 = 397.4 cm³
1. What is half- life? (1 mark)
  The time taken for a given mass/ amount of radioactive isotope to decay to half its original mass.
2. The half-life of protactinium - 234 is 117 minutes Determine the mass that decays in 585 minutes starting with 100 g of the sample (2 marks)
  N = (1)n
  N₀ 2
  n = 5.85 = 5
  1.17
  N = 1/2 ⁵
  100
  N = 1 x 100 = 3.125g
  2^⁵
State two disadvantages of hard water (2 marks)
- It stains white clothes
- Forms boiler scales that reduce the efficiency of boilers
- Wastes soap
Hydrogen chloride gas can be prepared by reacting sodium chloride with an acid
1. Name the acid (1 mark)
  Concentrated sulphuric (VI) acid
2. Write an equation for the reaction between sodium chloride and the acid (1 mark)
  
  NaCl (s) + H₂SO₄ (l) → NaHSO₄ (s) + HCl (g)
3. State two uses of hydrogen chloride (1 mark)
  - Used to clean metal surfaces
  - Used to make dyes, drugs and photographic materials such as silver bromide.
  - Sewage treatment
  - Water treatment
  - pH control and neutralisation in industries that require purity.
When solid B was heated strongly, it gave off water and a solid residue When water was added to the solid residue, the original solid B, was formed
1. What name is given to the process described? (1 mark)
  
  Temporary chemical change
2. Give one example of solid A (1 mark)
  
  Hydrated copper (II) sulphate
  
  Hydrated cobalt (II) chloride
The set up below can be used to prepare oxygen gas Study it and answer the questions that follow
1. Identify X (1 mark)
  Water
2. Write the equation for the reaction which occurs in the flask (1 mark)
  2Na₂O₂ (s) + 2H₂O (l) → 4NaOH (aq) + O₂ (g)
3. State one use of oxygen other than in welding (1 mark)
  - Air enriched with oxygen is used in hospitals for patients with breathing difficulties.
  - Oxygen mixed with helium is used by deep sea divers and mountain climber.
  - Used to burn rocket fuels
  - Used as one of the reactants in fuel cells
The atomic number of an element, M is 13
1. Write the electronic conﬁguration of the ion M³⁺ (1 mark)
  2.8
2. Write the formula of the chloride of M (1 mark)
  MCl₃
3. State the structure of the compound formed in (b) above (1 mark)
  Giant ionic structure
Concentrated sodium chloride was electrolysed using graphite electrodes Name the product formed at the anode and give a reason for your answer (2 marks)
Chlorine. Chloride ions are preferentially discharged due to high concentration.
The curve shown below shows the variation of time against temperature for the reaction between sodium thiosulphate and hydrochloric acid
1. Explain the shape of the curve (2 marks)
  
  Less time is taken for the reaction to take place at higher temperatures. As temperature increases, the kinetic energy of the reacting particles increases and this leads to higher frequency of effective collisions between the reacting particles, hence rate of reaction increases.
2. Other than temperature name one factor that affects the rate of reaction (1 mark)
  - Concentration
1. Dry ammonia was passed over heated copper (II) oxide in a combustion tube
  1. State the observations made in the tube (1 mark)
    Black solid changes to brown
  2. Write an equation for the reaction that occurs (1 mark)
    3CuO (s) + 2NH₃ (g) → 3Cu (s) + N₂ (g) + 3H₂O (l)
2. What products would be formed if red hot platinum is introduced into a mixture of ammonia and oxygen? (1 mark)
  Brown fumes are seen/ produced

The table below shows behaviour of metals P, Q, R and S Study it and answer the questions that follow:

Metal	Appearance on exposure to air	Reaction with water	Reaction with dilute sulphuric (VI) acid
P	Remains the same	Doesn’t react	Reacts moderately
Q	Remains the same	No reaction	Doesn’t react
R	Slowly tarnishes	Slow	Vigorous
S	Slowly turns white	Vigorous	Violent

Arrange the metals in the order of reactivity starting with the most reactive (2 marks)
S, R, P and Q
Name a metal which is likely to be R (1 mark)

Magnesium

Given the following substances: sodium carbonate, orange juice and sodium bromide
1. Name one commercial indicator that can be used to show whether sodium carbonate, orange juice and sodium bromide are acidic, basic or neutral (1 mark)
  - Phenolphthalein
  - Methyl orange
  - Litmus
  - Litmus papers
2. Classify the substances in 15 (a) above as acids, bases or neutral (2 marks)
  
  Acid
  
  orange juice
  
  Base
  
  sodium carbonate
  
  Neutral
  
  sodium bromide
The ﬂow chart below shows various reactions of zinc metal Study it and answer the questions that follow:
1. 1. Other than water, name another reagent that could be Q (1 mark)
    Excess sodium hydroxide
  2. Write the formula of reagent P (1 mark)
    HCl
2. Write an equation for the reaction in step 4 (1 mark)
  Zn (s) + H₂SO₄ (aq) → ZnSO₄ (aq) + H₂O (l)
1. One of the allotropes of sulphur is monoclinic sulphur, name the other allotrope (1 mark)
  Rhombic sulphur
2. Concentrated sulphuric (VI) acid reacts with copper and prapanol State the property of the acid shown in each case (2 marks)
  
  Copper ……oxidizing property
  
  Propanol …Dehydrating property

Study the standard electrode potentials in the table below and answer the questions that follow

Half -reaction	E ^θ(V)
Ag⁺(aq) + e → Ag(s)	+ 0.80
Cu²⁺(aq) + 2e → Cu(s)	+ 0.34
Mg²⁺(aq) + 2e → Mg(s)	- 2.38
Ca²⁺(aq) + 2e → Ca(s)	- 2.87

Which of the metals is the strongest oxidising agent? (1 mark)
Cu (s) / copper
What observations will be made if a copper coin was dropped into an aqueous solution of calcium nitrate? Explain (2 marks)
No change. Copper has a more positive electrode potential and hence it is a weaker reducing agent. Therefore, it cannot displace calcium ions from the calcium nitrate solution.

Calculate the number of sulphate ions present in 225 cm3 of 2 M aluminium sulphate solution (L=60 × 1023) (3 marks)
Al₂ (SO₄)₃
2 moles -> 1000 cm³
? -> 22.5 cm³
22.5 x 2 = 4.5 = 0.045 moles
1000 1000
0.045 x 3 = 0.135 moles
1 mol -> 6.0 x 10²³ ions
0.135mol -> ?
0.135 x 6.0 x 10²³
1
= 8.1 x 10 ^-22 ions
1. A crystal of iodine, heated gently in a test tube gave off a purple vapour
  1. Write the formula of the substance responsible for the purple vapour (1 mark)
    I₂
  2. What type of bond is broken when the iodine crystal is heated gently? (1 mark)
    Van der Waals forces of attraction
2. State one use of chlorine (1 mark)
  - Used in making PVC, aerosols (CFCs), Pesticides eg DDT
  - Used in water treatment
  - Used to manufacture hydrochloric acid
  - Used to manufacture bleaching agents
Describe how samples of barium (II) sulphate, ammonium chloride and common salt can be obtained from a mixture of the three (3 marks) Heat the mixture for ammonium chloride to dissociate into HCl gas and ammonia gas and recombine on a cool surface. Collect ammonium chloride. Add water to the remaining mixture and stir. Sodium chloride dissolves and barium sulphate remains undissolved. Filter the mixture to obtain barium (II) sulphate as the residue and sodium chloride as the filtrate. Rinse the residue and collect it. Heat the filtrate to evaporate the water and remain with solid common salt (sodium chloride).
1. Give the name of the process which takes places place when maize flour is converted to ethanol (1 mark)
  Fermentation
2. Write the formula of the compound formed when ethanol reacts with sodium metal (1 mark)
  C₂H₅ONa
1. Study the graph below which shows variation of atomic radius with atomic number
  
  State and explain the trend shown in the graph above (2 marks)
  Atomic radius increases from Lithium to potassium. Potassium has four occupied energy levels while sodium has three and lithium has only two.
2. State one use of sodium (l mark)
  - Sodium vapour is used in streetlights to give the yellow glow.
  - Sodium and potassium alloy is used as a coolant in nuclear reactors
A farmer intended to plant blueberries in her farm She first tested the pH of the soil and found it to be 100 In order to obtain high yield, what advice would be given to the farmer if blueberries do well in acidic solution? (2 marks)
The farmer should add acidifying substances such as vinegar and lemon.
Starting with calcium nitrate solution, describe how a pure dry sample of calcium carbonate can be prepared in the laboratory (3 marks)
Add sodium carbonate solution to calcium nitrate solution and stir. A precipitate of calcium carbonate is formed. Filter the mixture to obtain calcium carbonate as the residue. Rinse the residue with distilled water and dry it between filter papers.

A hydrocarbon contains 8182% of carbon If the molar mass of the hydrocarbon is 44, determine the molecular formula of the hydrocarbon (C = 120; H = 10) (3 marks)

Elements	Carbon	Hydrogen	(CH3)_n = 44 (12 + 3)_n = 44 15n = 44 n = 2.9 ≈ 3 ∴ C₃H₉
%	81.82	18.18
RAM	12	1
Moles	81.82/12 = 6.81	18.18/1 = 18.18
M.R	6.81 / 6.81 = 1	18.18 / 6.81 = 2.7
	1	3
E.F CH³

1. Describe how Carbon (II) Oxide can be distinguished from Carbon (IV) Oxide using calcium hydroxide solution (2 marks)
  Bubble the gases into separate test tubes with calcium hydroxide. The test tube in which a white precipitate is formed indicates that the gas is carbon (IV) oxide. No white precipitate when carbon (II) oxide is bubbled.
2. What is the role of carbon (IV) oxide in ﬁre extinguishing? (l mark)
  
  Carbon (IV) oxide does not support combustion and it is denser than air. It covers the flame cutting off oxygen supply and also extinguishes the flame.
1. Name one source of alkanes (1 mark)
  Crude oil
2. Methane gas was reacted with one mole of chlorine gas State the condition necessary for this reaction (1 mark)
  U.V. light
1. What is meant by heating value of a fuel? (1 mark)
  Heating value/ Calorific value of a fuel is the amount of energy given out when a unit mass of fuel is completely burnt in oxygen.
2. Other than heating value, name one factor to be considered when choosing a fuel (1 mark)
  - Availability
  - Ease of storage
  - Cost of the fuel
  - Environmental effects