Chemistry Paper 2 Questions and Answers - Form 4 Term 1 Opener Exams 2021

CHEMISTRY
PAPER 2
(THEORY)
FORM 4 TERM 1 OPENER EXAMS
TIME: 2 HOURS

INSTRUCTIONS TO CANDIDATES

Answer ALL the questions in the paper
Mathematical tables and silent electronic calculators may be used.
All questions should be answered in English.

1. The curves below represent the variation of temperature with time when pure and impure samples of a solid were heated separately.
  1. Which curve shows the variation in temperature for the pure solid? Explain. (2mks)
  2. State the effect of impurities on the melting and boiling points of a pure substance.
    1. Melting points (1 mk)
    2. Boilling points (1 mk)
2. The diagram below shows the relationship between the physical states of matter.
  1. Identify the processes B and D. (2mks)
    1. B………………………………………………
    2. D…………………………………………….
  2. Name process A (1mk)
  3. State two substances in chemistry that undergo the process A (1mk)
  4. Is the process E exothermic or endothermic? Explain (1mk)
Air was passed through several reagents as shown below
1. Name the main inactive component of air (1mk)
2. Name the components of air that are removed in the following chambers (3mks)
  1. Chamber 1
  2. Chamber 3
  3. Chamber 4
3. What is the purpose of passing air through concentrated sulphuric (vi) acid. (1mk)
4. Write a chemical equation for thereaction which takes place in :-
  1. chamber 1 (1mk)
  2. Chamber4 (1mk)
5. State and explain the observation made in chamber 3 during reaction (2mks)
6. Name one gas which escapes from the scheme above (1mk)
1. Draw and name two isomers of Pentane()
2. Study the flow diagram below and then answer the questions that follow.
  1. Name process J, K and T (3mks)
    1. J- ……………………………………………………………..
    2. K- …………………………………………………………….
    3. T- …………………………………………………………….
  2. State the reagents necessary for processed J and K (1mk)
  3. Name substances U, W, S and Y (4mks)
    1. U ……………………………………………………………….
    2. W ………………………………………………………………
    3. S ………………………………………………………………..
    4. Y ………………………………………………………………..
3. Describe how burning can distinguish CH₂CH₂ from CH₃CH₃ (2mks)
The grid below shows a part of the periodic table. The letters do not represent the actual symbols. Study it and answer the questions that follow.
1. Identify the elements in period 1 (1mk)
2. With a reason, identify the element with the largest atomic radius (2mks)
3. Draw the atomic structure of element Q (1mks)
4. Write down the electronic configurations of elements Y and W (2mks)
  1. Y- ……………………………………………………………………….
  2. W- ………………………………………………………………………
5. Element G forms an ion G^3- and its ionic configuration 2.8.8. indicate its position on the grid above (1mk)
6. Identify an element whose oxide reacts with both acids and alkalis (1mk)
7. 1. Write down the chemical formular of the compound formed between elements K and(1mk)
  2. Draw the bonding in the compound formed in (g) (i) above using dots (.) and crosses (x) to represent electrons (1mk)
8. Compare the atomic radius elements X and K. Explain (2mks)
1. Study the diagram below and answer the questions that follow
  1. Write a chemical equation for the reaction in tube A (1mk)
  2. Name the two salts formed in tube B (1mk)
  3. State the observation made in tube C (1mk)
  4. What is the purpose of potassium hydroxide in tube D. (1mk)
  5. Name gas P (1mk)
2. The flow chart below shows some industrial processes. Use it to answer the questions that follow
  1. Give the source of the following raw materials
    1. Nitrogen gas (1mk)
    2. Hydrogen gas (1 mk)
  2. Name the following substances;
    1. Catalyst P (1 mk)
    2. Gas M (1 mk)
    3. Liquid F (1 mk)
  3. Write the chemical equations for; formation of gas M. (1mk)
  4. The reaction in the absorption tower (1mk)
  5. State one use of nitric (v) acid (1 mk)
Below is a set of apparatus that was used to obtain a dry sample of sulphur(iv)oxide gas
1. Name;
  1. Solid W (1mk)
  2. The apparatus containing dilute hydrochloric acid (1mk)
2. State the role of Liquid Y (1mk)
3. Complete the diagram to show how the gas could have been collected (1mk)
4. A sample of sulphur(iv)oxide gas was passed through freshly prepared iron(III)sulphate solution. State and explain the observation made (2mks)
5. 50cm³ of 2M Hydrochloric acid was used during the above experiment. Determine the volume of sulphur(iv)oxide gas produced at r.t.p (molar gas volume = 24dm³) (3mks)
6. Other than manufacture of sulphuric(VI) acid state two other uses of sulphur(IV) oxide. (2mks)
1. Study the diagram below and answer the questions that follow:
  1. Name Liquids A and B
    1. A …………………………………………………………………………………… (1mk)
    2. B …………………………………………………………………………………… (1mk)
  2. Solid D can be anhydrous calcium chloride. Suggest another suitable reagent that can be used in place of anhydrous calcium chloride. (1mk)
  3. State the role of D suggested in (ii) above. (1mk)
  4. write a balanced equation for the reaction in the conical flask . (1mk)
  5. Explain why solid C collects further away from the heated aluminum metal. (1mk)
  6. In the combustion tube above 0.675g of aluminum metal reacted completely with 1800cm³ of chlorine gas at room temperature. Determine the molecular formula of solid C given that its relative formula mass is 267. (Al = 27, Cl = 35.5, Molar gas volume at r.t.p. = 24.0 litres) (3mks)
2. The reaction between hot concentrated sodium hydroxide and chlorine gas produces sodium chlorate (V) as one of the products
  1. give one use of sodium chlorate(V) (1mk)
  2. Explain the difference between bleaching by chlorine and by sulphur(IV) oxide gas. (1mks)
3. A solution of hydrogen chloride in water reacts with zinc carbonate but a solution of the gas in methylbenzene does not. Explain (2mks)

MARKING SCHEME

1. The curves below represent the variation of temperature with time when pure and impure samples of a solid were heated separately.
  1. Which curve shows the variation in temperature for the pure solid? Explain. (2mks)
    - Sharp/ constant melting point and boiling point.
  2. State the effect of impurities on the melting and boiling points of a pure substance.
    1. Melting points (1 mk) - lower the M.P √ 1
    2. Boilling points (1 mk) - raises the b.p√ 1
2. The diagram below shows the relationship between the physical states of matter.
  1. Identify the processes B and D. (2mks)
    1. B - Melting √1
    2. D - Condensation√1
  2. Name process A (1mk)
    - Sublimation √1
  3. State two substances in chemistry that undergo the process A (1mk)
    - Iodine √ ½
    - Ammonium chloride √ ½ Any two 1mk.
    - Solid ice √ ½
    - Iron (III) chloride√
    - Aluminum chloride √ ½
  4. Is the process E exothermic or endothermic? Explain (1mk)
    - Exothermic √ ½
    - Involves heat loss ½
Air was passed through several reagents as shown below
1. Name the main inactive component of air (1mk)
  - Nitrogen gas√ 1
2. Name the components of air that are removed in the following chambers (3mks)
  1. Chamber 1 - Carbon (iv) oxide gas√1
  2. Chamber 3 - Oxygen gas√1
  3. Chamber 4 - Nitrogen√1
3. What is the purpose of passing air through concentrated sulphuric (vi) acid. (1mk)
  - To remove/absorb water vapour or dry / drying agent.
4. Write a chemical equation for thereaction which takes place in :-
  1. chamber 1 (1mk)
    - 2 NaOH(Aq) +CO2(g) → Na2CO3(S)+H2O (L)√1
  2. Chamber4 (1mk)
    - 3Mg (s) +N2 (g) → Mg3N2(S)√1
      Penalize ½ if state symbols miss/wrong
      Penalize fully if not balanced.
5. State and explain the observation made in chamber 3 during reaction (2mks)
  - Brown solid changes to black√1
  - Brown copper metal oxidized/ reacts with oxygen to form copper (II) oxide (black)
6. Name one gas which escapes from the scheme above (1mk)
  - Argon
  - Neon
  - Helium
    Any one. (1mk)
1. Draw and name two isomers of Pentane
  
  Any two
  Drawing ½mk
  Naming ½mk
  Penalize fully if the structure is
  wrong
2. Study the flow diagram below and then answer the questions that follow.
  1. Name process J, K and T (3mks)
    1. J- Hydrogenation√1
    2. K- Bromination/Halogenation √1
    3. T- Polymerisation√1
  2. State the reagents necessary for processed J and K (1mk)
    - J-Hydrogen gas √ ½
    - K- Bromine gas √ ½
  3. Name substances U, W, S and Y (4mks)
    1. U - carbon (IV) Oxides gas √1
    2. W -chloroethane √ 1
    3. S - Polyethene√ 1
    4. Y - Sodium propanoate√ 1
3. Describe how burning can distinguish CH₂CH₂ from CH₃CH₃ (2mks)
  - CH₂CH₂ √ 1 burns with a yellow sooty flame while CH₃CH₃ √1 burns with a blue non- sooty flame.
The grid below shows a part of the periodic table. The letters do not represent the actual symbols. Study it and answer the questions that follow.
1. Identify the elements in period 1 (1mk)
  - C and T (Mark tied to the two elements)
2. With a reason, identify the element with the largest atomic radius (2mks)
  - J – has five energy levels/ highest number of energy levels.
3. Draw the atomic structure of element Q (1mks)
4. Write down the electronic configurations of elements Y and W (2mks)
  1. Y -2,8,8,2 √ 1
  2. W- 2,8,7√1
5. Element G forms an ion G3- and its ionic configuration 2.8.8. indicate its position on the grid above (1mk)
  - Period 3 should be shown on the grid
    Group 5 otherwise penalize fully
6. Identify an element whose oxide reacts with both acids and alkalis (1mk)
  - M
7. 1. Write down the chemical formular of the compound formed between elements K and(1mk)
    - K W₂
  2. Draw the bonding in the compound formed in (g) (i) above using dots (.) and crosses (x) to represent electrons (1mk)
8. Compare the atomic radius elements X and K. Explain (2mks)
  - K has a smaller √ ½ atomic radius than X
  - K has more √ ½ protons in the nucleus which increase the nucleus force of attraction √ ½ (higher nuclear charge) hence the electrons on the energy levels are strongly attracted towards the nucleus.
1. Study the diagram below and answer the questions that follow
  1. Write a chemical equation for the reaction in tube A (1mk)
    Heat
    - 2 Pb (NO₃)_2(S)→ 2 PbO_(s) +4 NO_{2 (g)} + O₂
    - Penalize ½ mk if state symbols miss /wrong
    - Penalize fully if not balanced
  2. Name the two salts formed in tube B (1mk)
    - Sodium nitrite√ ½
    - Sodium nitrate √ ½
  3. State the observation made in tube C (1mk)
    - Charcoal glow red hot √1
  4. What is the purpose of potassium hydroxide in tube D. (1mk)
    - To absorb Carbon (IV) oxide gas formed√1
  5. Name gas P (1mk)
    - Carbon (II) oxide gas √1
2. The flow chart below shows some industrial processes. Use it to answer the questions that follow
  1. Give the source of the following raw materials
    1. Nitrogen gas (1mk) - fractional distillation of liquid air√ 1
    2. Hydrogen gas (1 mk) - Electrolysis of brine
      Cracking of hydrocarbon
      Water gas√ 1
  2. Name the following substances;
    1. Catalyst P (1 mk) - rhodium √ 1
    2. Gas M (1 mk) - Nitrogen (II) Oxide √ 1
    3. Liquid F (1 mk) - water √ 1
  3. Write the chemical equations for; formation of gas M. (1mk)
    platinum
    4NH₃ +5O₂ → 4NO_(g) + 6H₂O_(l)
  4. The reaction in the absorption tower (1mk)
    4 NO_2(g) +2H₂O_(l)+O_2(g) → 4 HNO_3(aq)
  5. State one use of nitric (v) acid (1 mk)
    - Manufacture of nitrate fertilizers, synthetic fibre, dyes, drugs, explosives,
    - Purification of metals (Any one 1 mk).
Below is a set of apparatus that was used to obtain a dry sample of sulphur(iv)oxide gas
1. Name;
  1. Solid W (1mk)
    - Sodium sulphite
  2. The apparatus containing dilute hydrochloric acid (1mk)
    - Dropping funnel
2. State the role of Liquid Y (1mk)
  - Drying agent
3. Complete the diagram to show how the gas could have been collected (1mk)
4. A sample of sulphur(iv)oxide gas was passed through freshly prepared iron(III)sulphate solution. State and explain the observation made (2mks)
  - Yellow iron (III) sulphate solution √1 turned pale green sulphur (IV) oxide gas reduced iron (III) ions to iron (II) ions√1.
5. 50cm³ of 2M Hydrochloric acid was used during the above experiment. Determine the volume of sulphur(iv)oxide gas produced at r.t.p (molar gas volume = 24dm³) (3mks)
  - Na₂SO_3(S) + 2HCl_(aq) → 2 NaCl_(aq)+SO_2(g) + H₂O_(l)moles of HCl
    2 moles → 1000 cm³50 cm³√ (1 mk)
    ^(2×50)/₁₀₀₀=¹⁰⁰/₁₀₀₀ = 0.1moles
    Mole ratio Hcl : SO₂ 2 : 1 √ ½
    Moles of SO₂ = ¹/₂= 0.05moles
    1Mole → 24dm³moles ? = 1.2dm³√ ½
    2^(0.05×24)/₁√½
6. Other than manufacture of sulphuric(VI) acid state two other uses of sulphur(IV) oxide. (2mks)
  - to make calcium hydrogen sulphite used to bleach wood pulp in the manufacture of paper
  - as a fumigant
  - as a preservative in jam and fruit juices

Study the diagram below and answer the questions that follow:

Name Liquids A and B
1. - Concentrated hydrochloric acid(1mk)
2. - water(1mk)
Solid D can be anhydrous calcium chloride. Suggest another suitable reagent that can be used in place of anhydrous calcium chloride. (1mk)
- Calcium oxide/CaO (1mk)
State the role of D suggested in (ii) above. (1mk)
- to absorb unreacted/excess chlorine (1mk)
write a balanced equation for the reaction in the conical flask . (1mk)
- 2KMnO_4(S)+ 16HCl _(aq)→ 2KCl _(aq)+ 2MnCl_(aq) + 8H₂O_(l) + 5Cl_2(g)
Explain why solid C collects further away from the heated aluminum metal. (1mk)
- Solid C sublimes (1mk) hence collects on the cooler place away from heating

In the combustion tube above 0.675g of aluminum metal reacted completely with 1800cm³ of chlorine gas at room temperature. Determine the molecular formula of solid C given that its relative formula mass is 267. (Al = 27, Cl = 35.5, Molar gas volume at r.t.p. = 24.0 litres) (3mks)

Elements present	Al	Cl₂
MAss/Volume R.A.M/M.G.V No of moles Mole ratio	0.675 27 0.675/27 = 0.025 0.025/0.025= 1 EF=AlCl₃ ½mk	1800cm³ 24000cm³ 1800/24000= 0.075 ½mk 0.075/0.025 = 3 ½mk

(AlCl₃)n=267 ½mk
(27 + 35.5 x 3)_n = 267
n = ²⁶⁷/_133.5 = 2
M.F. = (AlCl₃)₂ = Al₂Cl₆ ½mk

The reaction between hot concentrated sodium hydroxide and chlorine gas produces sodium chlorate (V) as one of the products
1. give one use of sodium chlorate(V) (1mk)
  - bleaching agent in pulp
  - Used as herbicides Any one (1mk)
2. Explain the difference between bleaching by chlorine and by sulphur(IV) oxide gas. (1mks)
  - chlorine bleaches by addition of oxygen while sulphur (iv) oxide
A solution of hydrogen chloride in water reacts with zinc carbonate but a solution of the gas in methylbenzene does not. Explain (2mks)
- Hydrogen chloride gas dissociates in water to form an acidic solution which produces gas with zinc carbonate (1mk) while in methylbenzene the gas remains molecular hence the solution has no acidic properties and does not react with zinc carbonate (1mk)
- Bleaches by reduction ( 1mk)