Chemistry Paper 2 Questions And Answers - Form 4 Term 2 Opener 2021

INSTRUCTIONS TO CANDIDATES

Answer all the questions in the spaces provided.
All working must be clearly shown where necessary.
Scientific calculators may be used.

1. In an experiment to determine the percentage of oxygen in air, the apparatus below were set up. Study the set up and the information provided to answer thequestions that follow.
  
  A 500cm³ measuring cylinder K was filled with water and assembled for gas collection. Copper turnings were heated red hot and water was slowly passed into 500cm³ flask H until it reached the 500cm³ mark. A colourless gas was collected in K.
  1. What was the purpose of passing water into flask H? (1 mark)
  2. What observations were made in the tube I? (1 mark)
  3. Name one of the gases that is likely to be found in J. (1 mark)
  4. What was the volume of the gas collected in the measuring cylinder at the end of the experiment? (1 mark)
  5. Calculate the percentage of oxygen in air using the above results. (2 marks)
2. Study the diagram below and answer the questions that follow.
  1. Give one observation made in the combustion tube after some time. (1 mark)
  2. Write an equation for the formation of the colourless liquid Y. (1 mark)
  3. What was the aim of the above experiment as demonstrated in the combustion tube? Explain. (2 marks)

Use the information below to answer the questions that follow. The letters are not the actual symbols of the elements.

Element	Atmoic No.	M.P°C	B.P°C	Ionic radius (nm)
P	11	98	890	0.095
Q	12	650	1110	0.065
R	13	660	2470	0.050
S	14	1410	2360	0.041
T	15	44.2&590	280	0.034
U	16	113&119	445	0.184
V	17	−101	−35	0.181
W	18	−189	−186	-

1. Write the electronic configuration of the atoms represented by letters T and W. (1 mark)
2. State the nature of the oxides of the elements represented by Q and U. (2 marks)
Why does the elements represented by the letters T and U have two values of melting points? (1 mark)
Explain the following observations in terms of structure and bonding.
1. There is an increase in boiling point from P to R. (2 marks)
2. Element S has a high boiling point. (2 marks)
3. There is a decrease in boiling points from U to W. (2 marks)
1. Compare the atomic radius of U and V. (1 mark)
2. Why is there no ionic radius for W reported in the table? (1 mark)

The solubilities of potassium nitrate and potassium bromide at different temperatures was determined. The following data was obtained.

Temperature °C		0	10	20	30	40	50	60	70	80
Solubility g/100g H₂O	KNO₃	5	15	26	43	61	83	105	135	165
Solubility g/100g H₂O	KB_r	50	55	60	65	70	77	85	90	95

Draw solubility curves for both salts on the same axis. (3 marks)
What was the solubility of each salt at 65°C? (1 mark)
100g of a saturated solution of potassium nitrate at 70°C was cooled to 20°C. What mass of the crystals will be crystallized? (2 marks)

Study the flow chart below and answer the questions that follow.
1. Write an equation for the formation of solid A and gas B. (1 mark)
2. Name;
  Solution C - ………………………………………………….. (1 mark)
  Solid D - ………………………………………………….. (1 mark)
Write the formula of the complex ion in solution E. (1 mark)

Study the flow chart below and answer the questions that follow.
1. Name substance. (3 marks)
  X - ………………………………………………………………….
  Q - ………………………………………………………………….
  R - ………………………………………………………………….
2. Write down an equation for the reaction represented by step III. (1 mark)
3. What are the conditions and reagent required for steps?
  1. I (2 marks)
    Reagent - ………………………………………………………………………………….
    Condition - …………………………………………………………………………………..
  2. IV (2 marks)
    Reagent - …………………………………………………………………………………..
    Condition - …………………………………………………………………………………..
4. Name the process represented by: (4 marks)
  1. I - ……………………………………………………………………….
  2. II - ……………………………………………………………………….
  3. IV - ……………………………………………………………………….
  4. V - ……………………………………………………………………….
1. Study the scheme below and answer the questions that follow.
  1. Identify substances. (3 marks)
    1. A - …………………………………………………………………..
    2. B - …………………………………………………………………..
    3. D - …………………………………………………………………..
  2. State the catalyst necessary for; (2 marks)
    1. Step I - …………………………………………………………………………………………
    2. Step II - …………………………………………………………………………………………
  3. Write an equation for the reaction taking place in step II. (1 mark)
  4. Write two balanced chemical equations for the reaction between chlorine gas and;
    1. Hot and concentrated sodium hydroxide. (1 mark)
    2. Dilute and cold sodium hydroxide. (1 mark)
2. The diagram below shows an experiment in which the Lead (II) nitrate crystals are heated.
  1. Name; (2 marks)
    1. Liquid P - ………………………………………………………………………..
    2. Gas Y - ………………………………………………………………………..
  2. Write a balanced chemical equation for the decomposition of Lead (II) nitrate. (1 mark)
  3. Explain how you can distinguish between nitrogen (II) oxide and nitrogen (I) oxide. (2 marks)
1. Study the standard electrode potentials given below and answer the questions that follow.
  D²⁺ (aq) + 2e⁻ D(S) E^θ = −2.92V
  G²⁺ (aq) + 2e⁻ G(S) E^θ= −2.36V
  ½J²⁺ (g) + e⁻ J(S) E^θ = 0.00V
  M²⁺ (aq) + 2e⁻ M(S) E^θ = +0.34V
  ½R²⁺ (aq) + e⁻ R(S) E^θ = 2.87V
  1. Identify the strongest:
    1. Reducing agent ……………………….. (1 mark)
    2. Oxidizing agent ……………………….. (1 mark)
  2. Calculate the e.m.f of a cell made of G and M. (2 marks)
  3. Write the cell representation for the above cell in (b). (1 mark)
  4. Draw a cell diagram for the cell in (b) above. (2 marks)
  5. Write the cell reaction for the drawn cell diagram in (d) above. (1 mark)
2. Electrolysis of aqueous solution of metal M resulted in the deposition of 1.07g of metal upon passage of a current of 1.32 amperes for 75 minutes.(M = 52, 1F = 96500C)
  1. Calculate the quantity of electricity passed through the cell. (1 mark)
  2. Calculate the charge on the metal ion. (3 marks)
Extraction of iron involves two main processes, smelting and refining. Below is the blast furnace which is used to smelt iron from its ore.
1. 1. What does the word smelt mean? (1 mark)
  2. Name the reducing agent in the process. (1 mark)
  3. What is the role of the hot air blast in the process? (2 marks)
2. Write equations for the reactions that take place at the region marked A, B and C. (3 marks)
  A - ……………………………………………………………………………………………………….
  B - ……………………………………………………………………………………………………….
  C - ……………………………………………………………………………………………………….
3. What is the purpose of limestone in the extraction process? (1 mark)
4. Write equations to show how impurities are removed from the ore. (3 marks)

MARKING SCHEME

1. In an experiment to determine the percentage of oxygen in air, the apparatus below were set up. Study the set up and the information provided to answer the questions that follow.
  A 500cm3 measuring cylinder K was filled with water and assembled for gas collection. Copper turnings were heated red hot and water was slowly passed into 500cm3 flask H until it reached the 500cm3 mark. A colourless gas was collected in K.
  1. What was the purpose of passing water into flask H? (1 mark)
    To displace air in flask H over the hot copper turnings.
  2. What observations were made in the tube I? (1 mark)
    The brown solid changes to black
  3. Name one of the gases that is likely to be found in J. (1 mark)
    Nitrogen, carbon (IV) oxide, argon, (Xeron, neon) (Any one
  4. What was the volume of the gas collected in the measuring cylinder at the end of the experiment? (1 mark)
    410cm³
  5. Calculate the percentage of oxygen in air using the above results. (2 marks)
    (500 × 410) × 100 = 90 × 100 = 18%
    500 500
2. Study the diagram below and answer the questions that follow.
  1. Give one observation made in the combustion tube after some time. (1 mark)
    Black CuO turns to red-brown Cu.
  2. Write an equation for the formation of the colourless liquid Y. (1 mark)
    2H_2(g) + O_2(g) → 2H₂O_(l)
  3. What was the aim of the above experiment as demonstrated in the combustion tube? Explain. (2 marks)
    - To determine the reducing property of hydrogen. ✓1 Hydrogen is above Cu ✓1 in the reactivity series, thus it reduces the oxygen from CuO.
Use the information below to answer the questions that follow. The letters are not the actual symbols of the elements.
1. 1. Write the electronic configuration of the atoms represented by letters T and W. (1 mark)
    T - 2.8.5 ✓½
    W - 2.8.8 ✓½
  2. State the nature of the oxides of the elements represented by Q and U. (2 marks)
    Q - Basic Oxide ✓1
    U - Acidic oxide ✓1
2. Why does the elements represented by the letters T and U have two values of melting points? (1 mark)
  The two elements exhibit allotropy.
3. Explain the following observations in terms of structure and bonding.
  1. There is an increase in boiling point from P to R. (2 marks)
    There is gradual increase in the strength of the metallic bonds ✓1 due to the increase in the number of delocalized (valence) electrons in the element ✓1
  2. Element S has a high boiling point. (2 marks)
    The atomic radius of V is smaller than that of U. ✓1 V has more protons therefore has a stronger nuclear attraction hence the smaller atomic radius. ✓1
  3. There is a decrease in boiling points from U to W. (2 marks)
    Elements U, V and W have simple molecular structures ✓1 in which the molecules are held by weak Van der waals forces. The Van der waals ✓1 forces weaken from U to W.
4. 1. Compare the atomic radius of U and V. (1 mark)
    The atomic radius of V is smaller than that of U. ✓1
  2. Why is there no ionic for W reported in the table? (1 mark)
    It has a stable electron configuration hence does not ionize.
1. The solubilities of potassium nitrate and potassium bromide at different temperatures was determined. The following data was obtained.
  1. Draw solubility curves for both salts on the same axis. (3 marks)
  2. What was the solubility of each salt at 650C? of water (1 mark)
    - KBr 87g/100g of water ±1✓½
    - KNO₃ − 120g/100g of water ±1 ✓½
  3. 100g of a saturated solution of potassium nitrate at 70°C was cooled to 20°C. What mass of the crystals will be crystallized? (2 marks)
    At 70°C solubility = 135g/100g of water
    If 235g contain 135g of salt
    100g contain 135g
    100×135 = 57.4468g ✓½
    235
    At 20°C solubility = 26g/100g of water
    If 126g contain 26g of salt
    100g contain ?
    100×26 = 20.6349g ✓½
    235
    Mass which will crystallized
    57.4468 – 20.6349
    = 36.8119g
2. Study the flow chart below and answer the questions that follow.
  1. Write an equation for the formation of solid A and gas B. (1 mark)
    CuCO_3(s) CuO_(s) + CO_2(g)
  2. Name;
    Solution C - Copper (II) chloride (1 mark)
    Solid D - Copper (II) hydroxide (1 mark)
3. Write the formula of the complex ion in solution E. (1 mark)
  (Cu(NH₃)₄²⁺
Study the flow chart below and answer the questions that follow.
1. Name substance. (3 marks)
  X - Sodium ethonoate ✓1
  Q - Sodium ethoxide ✓1
  R - Iodoethane ✓1
2. Write down an equation for the reaction represented by step III. (1 mark)
  CH₃COOONa_(s) + NaOH_(aq) → CH_4(g) + Na₂CO_3(s)
3. What are the conditions and reagent required for steps?
  1. I (2 marks)
    Reagent - Propan-l-ol ✓1
    Condition - Conc. H₂SO₄ ✓1
  2. IV (2 marks)
    Reagent - Conc. H₂SO₄✓1
    Condition - Temp 160 – 180° ✓1
4. Name the process represented by: (4 marks)
  1. I - Esterification
  2. II - Substitution
  3. IV - Oxidation
  4. V - Dehydration
1. Study the scheme below and answer the questions that follow.
  1. Identify substances. (3 marks)
    1. A - Hydrogen
    2. B - Nitrogen
    3. D - NO
  2. State the catalyst necessary for; (2 marks)
    1. Step I - Iron finely divided / iron
    2. Step II - Platinum – rhodium catalyst
  3. Write a balanced chemical equation for taking place in step II. (1 mark)
    4NH_(g) + SO₂→ 2NO_(g) + 6H₂O
  4. Write two balanced chemical equations for the reaction between chlorine Gas and;
    1. Hot and concentrated sodium hydroxide. (1 mark)
      6NaOH_(aq) + 3Cl_2(g) → NaClO_3(aq) + 5NaCl_(aq) + H₂O_(l)
    2. Dilute and cold sodium hydroxide. (1 mark)
      2NaOH_(aq) + Cl₂ → NaOCl + NaCl + H₂O
2. The diagram below shows an experiment in which the Lead (II) nitrate crystals are heated.
  1. Name; (2 marks)
    1. Liquid P - dinitrogen tetra oxide
    2. Gas Y - oxygen
  2. Write a balanced chemical equation for the decomposition of Lead (II) nitrate. (1 mark)
    2Pb(NO₃)₂ → 2PbO_(s) + 4NO_2(s) + O_2(g)
  3. Explain how you can distinguish between nitrogen (II) oxide and nitrogen (I) oxide. (2 marks)
    - Nitrogen (V) oxide relights a glowing splint while nitrogen (II) oxide does not.
    - N₂O has xtic sweet smell, while. NO₂ is odourless.
1. Study the standard electrode potentials given below and answer the questions that follow.
  D²⁺ (aq) + 2e⁻  D(S) E^θ = −2.92V
  G²⁺ (aq) + 2e⁻  G(S) E^θ= −2.36V
  ½J²⁺ (g) + e⁻   J(S) E^θ = 0.00V
  M²⁺ (aq) + 2e⁻  M(S) E^θ = +0.34V
  ½R²⁺ (aq) + e⁻  R(S) E^θ = 2.87V
  1. Identify the strongest:
    1. Reducing agent D (1 mark)
    2. Oxidizing agent R²⁺ (1 mark)
  2. Calculate the e.m.f of a cell made of G and M. (2 marks)
    e.m.f = E^θR − E^θO
    =+0.34 − −2.36
    = +2.70V
  3. Write the cell representation for the above cell in (b). (1 mark)
    G_(s)/G²⁺_(aq)//M²⁺_(aq)/M_(s) ; E = +2.70V
    Penalize for lack of states and E value
  4. Draw a cell diagram for the cell in (b) above. (2 marks)
  5. Write the cell reaction for the drawn cell diagram in (d) above. (1 mark)
    G_(s)+ M²⁺_(aq)→ G²⁺_(aq) + M_(s) ; E = +2.70V
2. Electrolysis of aqueous solution of metal M resulted in the deposition of 1.07g of metal upon passage of a current of 1.32 amperes for 75 minutes.
  (M = 52, 1F = 96500C)
  1. Calculate the quantity of electricity passed through the cell. (1 mark)
    Q = 1t
    = 1.32 × 75 × 60 ✓½
    =5940C ✓½
  2. Calculate the charge on the metal ion. (3 marks)
    If 1.07g is departed by 5940C
    52g “ “
    52 × 5940 = 2888672.8972C ✓1
    1.07
    If 1F is 96500C
    ? “ 288672.8972C
    1 × 288672.8972 ✓1
    96500
    =2.994
    =3
    =+3 ✓1
Extraction of iron involves two main processes, smelting and refining. Below is the blast furnace which is used to smelt iron from its ore.
1. 1. What does the word smelt mean? (1 mark)
    - Extraction of a metal from its ore using a reducing agent and heat.
  2. Name the reducing agent in the process. (1 mark)
    - Carbon ( in form of coke)
  3. What is the role of the hot air blast in the process? (2 marks)
    - Hot air reacts with coke to form carbon (IV) oxide producing a lot of heat which melts the iron formed in the blast furnace.
2. Write equations for the reactions that take place at the region marked A, B and C. (3 marks)
  1. A
    C_(s) + O₍₂₎ → CO_2(g)
  2. B
    CO_2(g) + 3C_(s)→ 4Fe_(s) + 3CO_2(g)
  3. C
    2Fe₂O_3(s) + 3C_(s) → 4Fe_(s) + 3CO_2(g)
3. What is the purpose of limestone in the extraction process? (1 mark)
  - To remove silica impurities in the ore.
4. Write equations to show how impurities are removed from the ore. (3 marks)
  CaCO_3(s) CaO_(s) + CO_2(g)
  CaO_(s) + SiO_2(s) → CaSiO_3(s)
  Al₂O_3(s) + CaO_(s) → CaAl₂O_4(s)
  slag