Chemistry Paper 2 Questions and Answers - Pavement Mock Exams 2021/2022

INSTRUCTIONS TO CANDIDATES

• Answer all questions 
• Electronic calculators may be used

1. The grid below shows part of the periodic table. Study it and answer the questions that follow. The letters are not the actual symbols of the elements.
       
   
   1. Give the name of the family to which element F belongs. (1mark)
   2. Identify an element which forms a stable divalent anion (1mark)
   3. Give the formula of:
      1. The compound formed between A and B (½mark)
      2. The sulphate of H (½mark)
   4. Using dot (.) and cross(x) diagram, show the bonding in the compound formed between E and C. (2marks)
   5. Compare the atomic radii of elements C and D. Explain. (2marks)
   6. Select the element that has the lowest ionization energy. Explain. (1mark)
   7. 0.081g of element A reacts with 20cm³ of dilute hydrochloric acid. Calculate the molarity of the hydrochloric acid. (R.A.M = 27) (3marks)
   8. The graph below shows the trend of the melting points and the boiling points of the family to which element G belongs. Explain the trend in the melting points. (2marks)
      
2.  
   1.  
      1. What is a fuel? (1 mark)
      2. Calculate the heating value of propane, C₃H₈, given that its molar enthalpy of combustion is 2200 kJ mol^-1. . (2 marks)  (C=12, H=1)
   2.  
      1. Define molar enthalpy of combustion. (1 mark)
      2. Use the information provided by the thermochemical equations below to calculate the molar enthalpy of combustion of ethyne. (3 marks)
         C_(s) + O_2(g) → CO_2(g)            ∆H= -394 kJ mol^-1
         H_2(g) + ½O_2(g) → H₂O_(g)   ∆H= -286 kJ mol^-1
         2C_(s) + H_2(g) → C₂H_2(g)     ∆H= +226 kJ mol^-1
   3. Study the data given below and answer the questions that follow.
      

      Substance/ion	Enthalpy change
      CaCl2(s)	Lattice energy = −2237 kJ mol-1
      Ca2+(g)	Hydration energy = −1650 kJ mol-1
      Cl−(g)	Hydration energy = −364  kJ mol-1

      1. Determine the molar enthalpy of solution of calcium chloride in water. (2 marks)
      2. Draw an energy level diagram for the dissolution of calcium chloride in water. (3 marks)
3.  
   1. The diagram below shows the preparation of an oxide of nitrogen. Study the diagram and answer the questions that follow.
            
      1. Name the solid D. (1mark)
      2. Write the equation for the reaction in the flask M (1mark)
      3. Burning magnesium ribbon was lowered into the gas jar containing gas L. State and explain the observations made. (2marks)
      4. Write the two equations for the reactions taking place in (iii) above. (2marks)
      5. A drop of water was added to the product formed in (iii) above. A colourless gas K with a choking smell was produced. Write the chemical equation for the production of gas K (1mark)
   2.  
      1. Give two uses for nitric (V) acid. (2marks)
      2. A factory uses nitric (V) acid and ammonia gas as the only reactants for the preparation of ammonium nitrate. If the daily production of the ammonium nitrate is 4800kg, calculate the mass of ammonia gas used daily in kg. (N=14.0, O = 16.0 H= 1.0) (3 marks)
4. A group of form four students of Cockelbet Secondary School carried out an experiment to determine the solubility of potassium chlorate. The table below shows the results obtained.
   

   Total volume of water added(cm3)	10.0	.20.0	30.0	40.0	50.0
   Mass of KClO3(g)	5.0	5.0	5.0	5.0	5.0
   Temperature at which crystals appear(°C)	80.0	65.0	55.0	45.0	30.0
   Solubility of KClO3 (g/100gH2O)

   1. Complete the table to show the solubility of KClO₃ at different temperatures. (3marks)
   2. Plot a graph of mass of KClO₃ per 100g water against temperature at which crystals form.   (3marks)
   3. From the graph, determine ;
      1. The solubility of KClO₃ at 40°C. (1mark
      2. The temperature at which the solubility of KClO₃ is 35g/100g water. (1mark)
   4. Explain the shape of the graph. (1mark)
   5. State one application of solubility and solubility curves. (1mark)
5. The set up below is used to prepare Nitric (V) acid in the laboratory. Study it and answer the questions that follow.
           
   1. Complete the set-up. (3 marks)
   2. Name substances
      1. B………………………
      2. L ………………………(2 marks)
   3. Name apparatus A……………………………………………………………… (1 mark)
   4. Write an equation between substances B and L (1 mark)
   5. During preparation of hydrogen gas Nitric (V) acid is not used. Explain (2 marks)
   6. Give two commercial use of Nitrogen (2 marks)
6. The flow chart below is a simplified version of the steps in the manufacture of Sodium carbonate.
   
   1. Name three main raw materials of the above process. (3 marks)
   2. Name substance M. (1 mark)
   3. Name the process taking place in step II. (1 mark)
   4. Write a balanced chemical equation to show how product Y is formed. (1 mark)
   5. 98.123 Kg of Sodium hydrogen carbonate was manufactured in this process.
      1. Write a chemical equation for the formation of solid Z. (1 mark)
      2. Determine in Kilograms, how much of solid Z was produced in this process.
         (Na = 23, H = 1, O = 16, C = 12) (3 marks)
7.  
   1. Draw and name all the isomers of C₄H₆        (2marks)
   2. The following monomers react to form a polymer:
      
      Draw and name the structure of the polymer    (2marks)
   3. Chlorofluorocarbons have a wide range of uses. However they have been linked to depletion of ozone.
      1. Explain the problem caused by depletion of ozone layer. (1mark)
      2. Give one other environmental problem caused by chlorofluorocarbons. (1mark)
   4. Study the flow chart below and use it to answer the questions that follow.
      
      1. Name:
         1. Process W (½mark)
         2. Substances A, B and C (1½marks)
      2. Write an equation for the combustion of substance C (1mark)
      3. Give one use of gas A (1mark)
   5. Explain how a sample of propan-1-ol could be distinguished from a sample of propanoic acid by means of a chemical reaction (2marks)

MARKING SCHEME

1.  
   1. Alkaline-earth metals (1mark)
   2. B (1mark)
   3.  
      1. A₂B₃     (½mk)
      2. H₂SO₄     (½mark)
   4.  
      
      Distribution of electrons (1mk) and charges (1mk)
      No label (0mk)
   5.  
      • D has a smaller atomic size than C//C has larger atomic size than D (1mark)
      • D has more protons than C//D has stronger nuclear charge than C (1mark)
   6. H (½mk). Loses electrons most readily/largest atomic radius/weakest nuclear charge (explanation ½mk)
   7. 2A_(s) + 6HCl_(aq) → 2ACl_3(aq) + 3H_2(g)            1mark
      Moles of A = 0.081  = 0.003moles ½mark
                              27
      Mole ratio 1:3
      Moles of HCl = 0.003 x 3 = 0.009moles ½mark
      0.009×1000   ½mk = 0.45M ½mark
             20
   8. The melting point increase with increase in atomic number. 1mark
      This is due to increase in the strength of van der waal’s forces (inter-molecular forces) 1mark
2.  
   1.  
      1. A fuel is a substance that can be used as a source of energy. (1 mark)
         OR A substance that produces useful energy when it undergoes a chemical or nuclear reaction.
      2. Molar mass of C₃H₈ = 12 x 3 + 1 x 8= 44 g/mol^-1      ½mark
         Heating value = 2200    1 mark
                                      44
         = 50 kJ/g ½mark
   2.  
      1. molar enthalpy of combustion is the heat change when one mole of a substance is burnt completely in oxygen. (1mark)
      2.  
         
         ∆HC_(ethyne)= −(+226) + 2(−394)+ (−286) (1 mark)
         = −226−788−286
         = −1300 kJ/mol^-1 (1 mark)
   3.  
      1. ∆H_soln = −(−2237) + −1650)+ (2 x −364) (1 mark)
                    = −141 kJ mol^-1 (1 mark)
      2.  
          (3 marks)
3.  
   1.  
      1. Potassium nitrate (Reject KNO₃) (1mark)
      2. (NH₄)₂SO_{4 (S)} + 2KNO_3(s) → K₂SO_4(s) +2H₂O_(l) +N₂O_(g) (1mk)
      3. The magnesium ribbon continues to burn with a dazzling flame forming white solid .(1mark)
         This is because burning magnesium produces sufficient heat to dissociate nitrogen (I) oxide into oxygen and nitrogen gases (½mk). The oxygen supports combustion of magnesium to form white magnesium oxide while nitrogen combines with hot magnesium metal to form white magnesium nitride. (½mark)
      4.  
         1. 2Mg_(s) + O_2(s) →  2MgO_(s) (1 mark)
         2. 3Mg_(s) + N_2(g) →  Mg₃N^2(s) (1 mark)
      5. Mg₃N_2(s) + 6H₂O_(l) →  3Mg(OH)_2(s) + 2NH_3(g) (1mark)
   2.  
      1.  
         • Manufacture of nitrogenous fertilizers such as ammonium nitrate. (any two correct uses)
         • Manufacture of textile dyes
         • Manufacture of explosives
      2. HNO_3(l) + NH_3(g) → NH₄NO_3(s)      √ 1mk
         Mole ratio: 1:1:1
         Molar mass of ammonia = 17g
         Molar mass of ammonium nitrate = 80g    √½mk
         80g NH₄NO₃ →   17g
         4800000g      →     17x4800000 = 1020000g
                                                80                      √1mk
         = 1020kg of ammonia gas. √½mk
4.  
   1. Total volume of water added(cm3) 

      Total volume of water added(cm3)	10.0	.20.0	30.0	40.0	50.0
      Mass of KClO3(g)	5.0	5.0	5.0	5.0	5.0
      Temperature at which crystals appear(°C)	80.0	65.0	55.0	45.0	30.0
      Solubility of KClO3 (g/100gH2O)	50.0✓½	25.0✓½	16.7✓½	12.5✓½	10.0✓½

      NB: √½mk for expressing solubility values to the same number of decimal points
   2. Graph marking points:
      • scale (graph to cover ˃= ½ grid)√½
      • Labeling of axes√½
      • Plotting of points √1
      • Curve (smooth) √1
   3.  
      1. 11g/100gH₂O √1
      2. 72°C (± 0.5)√1
   4. Solubility of KClO₃ increases with increase in temperature/more KClO₃ dissolves as temperature rises√1
   5.  
      • Extraction of soda ash(Sodium carbonate) from Trona√1
      • Extraction of common salt(sodium chloride). Etc.
5.   
   1.  
      
   2.  
      1. B – Sodium Nitrate/KNO₃✔1
      2. L – Concentrated H₂SO₄✔1
   3. A – Retort Flask✔1
   4. NaNO_3(s) + H₂SO_4(l) → HNO_3(aq) + NaHSO_4(aq) ✔1
   5. HNO₃ is a powerful✔1 oxidizing agent. It oxides H2 ✔1 to water.
   6.  
      • Semen storage for artificial insemination.✔1
      • Manufacture of ammonia in the Haber process✔1
6.  
   1.  
      • Ammonia gas
      • Limestone / calcium carbonate
      • Brine / concentrated sodium chloride
   2. Ammonia gas
   3. Filtration
   4. 2NH₄Cl_(aq) + Ca(OH)_2aq → CaCl₂ + 2H₂O_(l) + 2NH₃
   5.  
      1. 2NaHCO_3(s) → Na₂CO_3(s) + H₂O_(l) + CO_2(g)
      2. From equation: 2 moles NaHCO₃ produces 1 mole Na₂CO₃
         R.F.M of NaHCO₃ is (1 x 23) + (1x1) + (1 x 12) + (3 x16) = 84
         (^84g/_1000g x 1) kg is 0.084 kg
         2 mole NaHCO3 is 0.084 x 0.168 kg
         R.F.M of Na₂CO₃ is (2 x 23) + (1 x 12) + (3 x 16) = 106
         (^106g/_1000g x 1 kg) is 0.106 kg
         If, 0.168 kg NaHCO₃ produces 0.106 kg
         98.128       produces (98.128 x 0.106 )
                                                    0.168
         = 61.9109Kg Solid Z
7.   
   1.  
      
          But – 1 – yne                            But – 2 – yne (structure ½mk, name ½mk total 2mks)
   2. Nylon 6,6. 1mk
      1mk
   3.  
      1. Harmful rays from the sun reaches the earth’s surface causing harm to humans 1mk
      2. Contribute to global warming 1mk
   4.  
      1.  
         1. Oxidation (½mk)
         2.  
            • A: Propene
            • B: Sodium propanoate
            • C: Ethane (1½mk)
      2. 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O (1mk)
      3.  
         • Used in manufacture of polypropene used in making ropes, plastic crates, buckets, basins, plastic tables and chairs etc
         • Manufacture of other chemicals e.g. acetone, propan-1-ol etc
         • Used as an alternative to ethyne(acetylene) in welding flame
   5. Add sodium carbonate/ sodium hydrogen carbonate to separate samples of each 1mk. Propanoic acid produces bubbles of a gas/effervescence/fizzling while propan-1-ol does not 1mk