Chemistry Paper 1 Questions and Answers - Form 3 Term 3 Opener Exams 2023

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Kiswahili Paper 3 Questions and Answers - Form 3 Term 3 Opener Exams 2023

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Explain how the hotness of a Bunsen Burner flame can be increased. (1mk)
The set-up below represents the apparatus that may be used to separate a mixture of two miscible liquids C and D whose boiling points are 80°C and 110°C. (1mk)
1. Name B. (1mk)
2. What is the purpose of the thermometer? (1mk)
3. Which liquid was collected in the test tube? Explain (1mk)
4. State the method used in separating mixtures C and D above. (1mk)
A student accidentally mixed potassium chloride with white sand in the laboratory. Briefly describe how the mixture can be separated. (3mks)
The table below gives the number of electrons, protons and neutrons in substance X, Y and Z. study it and answer the questions that follow.

Substance Electrons Protons Neutrons

X 10 10 10

Y 10 8 10

Z 8 8 8
1. Which letters represent an ion? (1mk)
2. Which of the substances are isotopes? Explain. (2mks)
3. Calculate the mass number of substance Y. (1mk)
1. Name a suitable solvent for extracting an indicator from flowers. (1mk)
2. Give a reason why the solvent named in (a) above is used. (1mk)
The following set up of three- test tubes was used to investigate rusting of iron. Study it and answer the questions that follow.
1. Give a reason why rusting did not occur in test-tube C. (1mk)
2. What would be the effect of putting the iron nails in water into which some crystals of sodium chloride have been added? Explain. (2mks)
Describe how the following reagents can be used to prepare Lead Sulphate: solid potassium sulphate, solid lead carbonate, dilute nitric (V) acid and distilled water. (3mks)
Charcoal is a fuel that is commonly used for cooking. When it burns, it forms two oxides.
1. Name the two oxides. (2mks)
2. For each oxide identified state one use. (2mks)
1. State the Boyle’s law. (1mk)
2. A gas occupies 500cm³ at 27°C and 100,000 Pa. What will be its volume at 0°C and 101,325 Pa? (3mks)
On strong heating of potassium nitrate it liberates oxygen gas. In the space provided below, draw a labeled diagram of a set up that could be used for heating potassium nitrate and collecting the oxygen gas liberated. (3mks)
On complete combustion of a sample of hydrocarbon, 3.52g of carbon (IV) oxide and 1.44g of water were formed. Determine the molecular formula of the hydrocarbon. (relative molecular mass of hydrocarbon = 56, C=12, H=1) (3mks)
Study the flow chart below and answer that questions that follow.
1. Name the suitable drying agent for ammonia. (1mk)
2. Describe one chemical test for ammonia. (1mk)
3. Name Y. (1mk)
Nitrogen is inert. State one use of the gas based on this property. (1mk)
1. What is meant by Isomerism? (1mk)
2. Draw and name two Isomers of butane. (2mks)
3. Give the name of the substance CH ≡ CH (1mk)
Given that the atomic number of element Y is 13 and that of Z is 9.
1. Write the electronic arrangement of Y and Z. (1mk)
2. Draw the dot (.) and cross (x) diagram for the compound formed by Y and Z. (2mks)
3. Which type of structure is formed in the compound formed above? (1mk)
12.0cm³ of 0.05m hydrochloric acid reacted with calcium hydrogen carbonate to form calcium chloride, water and carbon IV oxide.
1. Write the chemical equation for the reaction. (1mk)
2. Calculate the number of moles of hydrochloric acid used. (2mks)
3. Determine the number of moles of calcium hydrogencarbonate used. (1mk
Study the flow chart below and answer the questions that follow.
1. Name:
  1. Gas V (1mk)
  2. Solid w (1mk)
Ethanedioic acid (COOH)₂ is used instead of methanoic acid (HCOOH) to prepare carbon (II) oxide in the laboratory. The reaction produces equal volumes of carbon (II) oxide and carbon (IV) oxide.
1. If water is one of the products, write an equation for the dehydration of ethanedioic acid. (1mk)
2. How can pure carbon (II) oxide be obtained from the mixture of the two gases? (2mks)
When fuels burn in the internal combustion engine at high temperature, one of the products formed is nitrogen (II) oxide.
1. Write an equation for the formation of nitrogen (II) oxide. (1mk)
2. Give a reason why nitrogen (II) oxide is not formed at room temperature. (1mk)
3. Describe how formation of nitrogen (II) oxide in the internal combustion engine leads to gaseous pollution. (1mk)
Sulphur exists in two crystalline forms.
1. Name one crystalline form of sulphur. (1mk)
2. State two uses of sulphur (IV) oxide. (2mks)
Ammonia gas was passed into water as shown below.
1. Explain why the pH of the solution is above 7. (1mk)
2. What is the use of the inverted funnel? (1mk)
20.0cm³ of a solution containing 4g per litre of sodium hydroxide was neutralized by 8.0cm³ of dilute sulphuric (VI) acid. Calculate the concentration of sulphuric (VI) acid in moles per litre. (Na=23, O=16, H=1, S=32) (3mks)
Write balanced equations for the decomposition of:
1. Ammonium carbonate. (1mk)
2. Lead (II) nitrate (1mk)
The set up below was used to collect gas F, produced by the reaction between water and calcium metal.
1. Name gas F (1mk)
2. State the confirmatory test for the gas. (1mk)
3. State the nature of the solution formed in the beaker. (1mk)
Name an appropriate apparatus that is used to prepare standard solutions in the laboratory. (1mk)
Explain why there is a general increase in the first ionization energies of the elements in period 3 of the periodic table from left to right. (2mks)
Dilute hydrochloric acid and sodium sulphite was reacted in the laboratory fume chamber.
1. Name the gas that was produced. (1mk)
2. Write the equation for the reaction which took place. (1mk)
When a sample of concentrated sulphuric (VI) acid was left in an open beaker in a room for two days the volume was found to have increased slightly.
1. What property of concentrated sulphuric (VI) acid is shown by the above reaction? (1mk)
2. State one use of concentrated sulphuric (VI) acid that depends on the property named above. (1mk)
When chlorine gas dissolves in water it forms chlorine water which appears yellow. Identify the components of chlorine water. (1mk)

MARKING SCHEME

Explain how the hotness of a Bunsen Burner flame can be increased. (1mk)
- By keeping the air hole fully open
The set-up below represents the apparatus that may be used to separate a mixture of two miscible liquids C and D whose boiling points are 80°C and 110°C. (1mk)
1. Name B. (1mk)
  - Liebig’s condenser
2. What is the purpose of the thermometer? (1mk)
  - To show which vapour fractions are distilling off.
3. Which liquid was collected in the test tube? Explain (1mk)
  - Liquid C, it has a lower boiling point (80°C) then that of D (110°C) hence distills off first.
4. State the method used in separating mixtures C and D above. (1mk)
  - Fractional disstillation
A student accidentally mixed potassium chloride with white sand in the laboratory. Briefly describe how the mixture can be separated. (3mks)
- add water to the mixture to dissolve sodium chloride. Filter to obtain sand as residue and potassium chloride as filtrate. Evaporate the filtrate to obtain crystals of potassium chloride.
The table below gives the number of electrons, protons and neutrons in substance X, Y and Z. study it and answer the questions that follow.

Substance Electrons Protons Neutrons

X 10 10 10

Y 10 8 10

Z 8 8 8
1. Which letters represent an ion? (1mk)
  - Y
2. Which of the substances are isotopes? Explain. (2mks)
  - Y and Z; their proton / atomic number is the same.
3. Calculate the mass number of substance Y. (1mk)
  - Mass number = No. of protons + No. of neutrons
    = 8 +10
    = 18
1. Name a suitable solvent for extracting an indicator from flowers. (1mk)
  - Propanone or acetone
2. Give a reason why the solvent named in (a) above is used. (1mk)
  - It is able to dissolve components in the flowers.
The following set up of three- test tubes was used to investigate rusting of iron. Study it and answer the questions that follow.
1. Give a reason why rusting did not occur in test-tube C. (1mk)
  - There was no oxygen needed/necessary for rusting to take place since boiling water removes dissolved oxygen.
2. What would be the effect of putting the iron nails in water into which some crystals of sodium chloride have been added? Explain. (2mks)
  - The highest amount of rusting would be observed. Presence of salt accelerates/increase the process of rusting.
Describe how the following reagents can be used to prepare Lead Sulphate: solid potassium sulphate, solid lead carbonate, dilute nitric (V) acid and distilled water. (3mks)
- Dissolve potassium sulphate in distilled water to obtain K₂SO₄ solution; add excess PbCO₃ to dilute HNO₃ acid and stir. Filter to obtain Pb(NO₃)₂ as filtrate. Mix pb(NO₃)₂ and K2SO₄ solution to precipitate PbSO₄. Filter and wash the residue with distilled water and dry it between filter papers.

Charcoal is a fuel that is commonly used for cooking. When it burns, it forms two oxides.

Name the two oxides. (2mks)
- Carbon (IV) oxide
- Carbon (II) oxide

For each oxide identified state one use. (2mks)

Carbon (IV) oxide	Carbon (II) oxide
Manufacture of soft drinks	In extraction of iron/metal from it ore
Used in fire extinguishers	Used as a fuel
Used in refrigeration as dry ice

1. State the Boyle’s law. (1mk)
  - The volume of a fixed mass of a gas is inversely proportional to its pressure at constant temperature.
2. A gas occupies 500cm³ at 27°C and 100,000 Pa. What will be its volume at 0°C and 101,325 Pa? (3mks)
  P1= 100,000Pa
  V1= 500cm3
  T1= (27 + 273) = 300K
  P2= 101325 Pa
  T2= ( 0 + 273) = 273
  V2=?
  P1V1= P2V2
  T1 T2
  V2= P₁V₁T₂
  P₂T₁V₂= 100,000 x 500 x 273
  101325 x 300
  = 449cm³
On strong heating of potassium nitrate it liberates oxygen gas. In the space provided below, draw a labeled diagram of a set up that could be used for heating potassium nitrate and collecting the oxygen gas liberated. (3mks)
- To be assessed by the teacher.
On complete combustion of a sample of hydrocarbon, 3.52g of carbon (IV) oxide and 1.44g of water were formed. Determine the molecular formula of the hydrocarbon. (relative molecular mass of hydrocarbon = 56, C=12, H=1) (3mks)
Mass of C = 12 x 3.52 = 0.96g
44
Mass of H = 2 x 1.44 = 0.16g
18
Elements C H
Mass (g) 0.96 0.16
RAM 12 1
Moles 0.96 0.16
12 1
0.08 0.16
Ratio 0.08 0.16
0.08 0.08
1 : 2
E.F : CH2
(CH₂)n = 56
14n = 56
14 14
n=4
M.F = (CH₂)₄
= C₄H₈
Study the flow chart below and answer that questions that follow.
1. Name the suitable drying agent for ammonia. (1mk)
  - Calcium oxide
2. Describe one chemical test for ammonia. (1mk)
  - It forms dense white fumes of ammonium chloride when reacted with hydrogen chloride gas.
3. Name Y. (1mk)
  - Water
Nitrogen is inert. State one use of the gas based on this property. (1mk)
- Used to fill light bulbs to prevent the oxidation of the filament.
- In storage of semen for artificial insermination.
1. What is meant by Isomerism? (1mk)
  - Existence of compounds with same molecular formula but different structural formulae.
2. Draw and name two Isomers of butane. (2mks)
3. Give the name of the substance CH ≡ CH (1mk)
  - Ethyne
Given that the atomic number of element Y is 13 and that of Z is 9.
1. Write the electronic arrangement of Y and Z. (1mk)
  - Y = 2.8.3
  - Z = 2.7
2. Draw the dot (.) and cross (x) diagram for the compound formed by Y and Z. (2mks)
3. Which type of structure is formed in the compound formed above? (1mk)
  - Giant ionic
12.0cm³ of 0.05m hydrochloric acid reacted with calcium hydrogen carbonate to form calcium chloride, water and carbon IV oxide.
1. Write the chemical equation for the reaction. (1mk)
  Ca(HCO₃)_2(aq) + 2HCl_(aq) → CaCl_2(aq) + 2H₂O_(l) + 2CO_2(g) ✔1
  - unbalanced eqn. – zero mk
  - Penalise ½ mk for wrong or missing s.s
2. Calculate the number of moles of hydrochloric acid used. (2mks)
  Moles of HCl = 12 × 0.05 ✔ ½ = 0.0006mol ✔ ½
  1000
3. Determine the number of moles of calcium hydrogencarbonate used. (1mk)
  Moles of Ca(HCO₃)₂ = ½ x 0.0006 ✔ ½
  = 0.0003mol ✔ ½
Study the flow chart below and answer the questions that follow.
1. Name:
  1. Gas V (1mk)
    - Hydrogen chloride
  2. Solid w (1mk)
    - Ammonium chloride
Ethanedioic acid (COOH)₂ is used instead of methanoic acid (HCOOH) to prepare carbon (II) oxide in the laboratory. The reaction produces equal volumes of carbon (II) oxide and carbon (IV) oxide.
1. If water is one of the products, write an equation for the dehydration of ethanedioic acid. (1mk)
  - (COOH)_2(s) Conc → CO_2(g) + CO_(g) + H₂O H2SO4(l)
2. How can pure carbon (II) oxide be obtained from the mixture of the two gases? (2mks)
  - By passing the mixture through a concentrated solution of potassium/sodium hydroxide, carbon (IV) oxide is absorbed leaving behind the carbon (II) oxide.
When fuels burn in the internal combustion engine at high temperature, one of the products formed is nitrogen (II) oxide.
1. Write an equation for the formation of nitrogen (II) oxide. (1mk)
  - N_2(g) + O_2(g) → 2NO_(g)
2. Give a reason why nitrogen (II) oxide is not formed at room temperature. (1mk)
  - Nitrogen atoms in the molecule are joined by strong triple covalent bond that requires a lot of energy to break than provided at room temperature.
3. Describe how formation of nitrogen (II) oxide in the internal combustion engine leads to gaseous pollution. (1mk)
  - Nitrogen (II) oxide reacts with oxygen in the air to form nitrogen (IV) oxide that dissolves in water vapour to form acid rain.
Sulphur exists in two crystalline forms.
1. Name one crystalline form of sulphur. (1mk)
  - Rhombic sulphur, monodinic sulphur
2. State two uses of sulphur (IV) oxide. (2mks)
  - As a bleaching agent
  - As raw material for manufacture of sulphuric (VI) acid.
  - As a fumigant
  - To make Ca(HSO₃)₂ used to bleach wood pulp in paper manufacture.
Ammonia gas was passed into water as shown below.
1. Explain why the pH of the solution is above 7. (1mk)
  - Because ammonia is basic, it dissolves in water to form a basic solution.
2. What is the use of the inverted funnel? (1mk)
  - To prevent sucking back of water as ammonia is very soluble by providing a large surface area for dissolution.
20.0cm³ of a solution containing 4g per litre of sodium hydroxide was neutralized by 8.0cm³ of dilute sulphuric (VI) acid. Calculate the concentration of sulphuric (VI) acid in moles per litre. (Na=23, O=16, H=1, S=32) (3mks)
H₂SO_4(aq) + 2NaOH_(aq) → Na₂SO_4(aq) + H₂O_(l)
M_aV_a = moles of a
M_bV_b moles of b
M_a × 8
0.1 × 20
Ma = 0.1 × 20
8 × 2
Ma = 0.125m
Write balanced equations for the decomposition of:
1. Ammonium carbonate. (1mk)
  - (NH₄)₂CO_3(s) 2NH_3(g) + CO_2(g) + H₂O^(g)
2. Lead (II) nitrate (1mk)
  - 2Pb(NO₃)_2(s) 2PbO(s) + 4NO_2(g) + O_2(g)
The set up below was used to collect gas F, produced by the reaction between water and calcium metal.
1. Name gas F (1mk)
  - Hydrogen
2. State the confirmatory test for the gas. (1mk)
  - It extinguishes a burning splint with a pop sound.
3. State the nature of the solution formed in the beaker. (1mk)
  - Alkaline / basic
Name an appropriate apparatus that is used to prepare standard solutions in the laboratory. (1mk)
- Volumetric flask
Explain why there is a general increase in the first ionization energies of the elements in period 3 of the periodic table from left to right. (2mks)
- Across the period there is a gradual increase in number of protons in the nucleus. This increases the force of attraction between the nucleus and the electrons.
Dilute hydrochloric acid and sodium sulphite was reacted in the laboratory fume chamber.
1. Name the gas that was produced. (1mk)
  - Sulphur (IV) oxide
2. Write the equation for the reaction which took place. (1mk)
  - Na₂SO_3(s)+ 2Hcl_(aq) SO_2(g)+ 2NaCl_(aq) +H₂O_(l)
When a sample of concentrated sulphuric (VI) acid was left in an open beaker in a room for two days the volume was found to have increased slightly.
1. What property of concentrated sulphuric (VI) acid is shown by the above reaction? (1mk)
  - Hygroscopy
2. State one use of concentrated sulphuric (VI) acid that depends on the property named above. (1mk)
  - Used as a drying agent
When chlorine gas dissolves in water it forms chlorine water which appears yellow. Identify the components of chlorine water. (1mk)
- Hydrochloric acid
- Chloric (1) acid / hypochlorous acid