Chemistry Paper 2 Questions and Answers - Maranda High Pre Mock Exams 2023

Instructions to candidates  

• Answer all the questions in the spaces provided in the question paper.
• KNEC mathematical tables and electronic calculators may be used for calculations. (d)All workings MUST be clearly shown where necessary.
• Candidates should answer the questions in English.  

1.  
   1. Study the diagram below and use it to answer the questions that follow. 
      
      1. Name liquids A and B 
         A………………………………………………………………(½mark) B…………………………………………………………….( ½mark)
      2. Suggest the most suitable reagent that can be used as solid D (1 mark) ………
      3. State the role of Solid D (1 mark)
      4. Write a balanced chemical equation for the reaction in the conical flask. (1mark)
      5. Explain why solid C collects further away from the heated Aluminium metal. (1mark)
      6. In the combustion tube above, 0.675g of Aluminium 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= 27.0, Cl= 35.5 molar gas volume at r.t.p = 24.0 litres) . (3marks)
   2. The reaction between hot concentrated sodium hydroxide and chlorine gas produces Sodium Chlorate (V) as one of the products
      1. Write the equation for the reaction. (1mark)
      2. Give one use of sodium chlorate.(V) (1mark)
   3. Explain the difference between bleaching by chlorine and bleaching by Sulphur (IV)oxide gases.  (2marks)
2. The grid below represents part of the periodic table. Study it and answer the questions that follow.  Letters are not the actual symbols of the elements. 
   
   1. Select a letter that represents the most reactive non-metal. Explain (2 marks)
   2. Select a letter that represents an element that forms an ion with a charge of 2^- (1 mark)
      1. Select an alkaline earth metal (1 mark)
      2. Which group I element has highest first ionization energy? Explain (2 marks)
   3. What is the formula of the compound formed when V reacts with X? (1 mark) _visit 
   4. What type of chemical bond exists in a compound formed when R and S react? (1 mark)
   5. Explain why the atomic radius of S is smaller than that of Q. (2 marks)
   6. State and explain the observation made when sodium carbonate is added to a chloride solution of element V.  (2 marks)
3.  
   1. The table below shows the solubility of potassium chlorate at different temperatures 
      

      Temperature (oC )	10o	20o	30o	40o	50o	60o	70o
      Solubility g/100g water	27	30	36	55	80	110	140

      1. Plot a graph of solubilities of potassium chlorate against temperature (3 marks)
      2. Using your graph:  
         1. Determine the solubility of potassium chlorate at 47^oC (1 mark)
         2. Determine the concentration in moles per litre of potassium chlorate at 47^oC  
            (K= 39, Cl = 35.5, O= 16) density of solution = 1g/cm³ (1 mark)
         3. Determine the mass of potassium chlorate that would crystallize if the solution is  cooled from 62^oC to 45^oC. (2 marks)
   2. In an experiment to determine the solubility of sodium hydroxide, 25cm³ of a saturated solution of sodium  hydroxide weighing 28g was diluted in a volumetric flask and the volume made to 250cm³ mark. 20cm³ of this  reacted completely with 25cm³ of 0.2M hydrochloric acid according to the equation.
      NaOH_(aq) + HCl_(aq)  NaCl_(aq) + H₂O(l) 
      Calculate: 
      1. The number of moles of hydrochloric acid used (1 mark)
      2. The number of moles of sodium hydroxide in 20cm³ (1 mark)
      3. The moles of sodium hydroxide in 250cm³ of solution (1 mark)
      4. The mass in grams of sodium hydroxide in 250cm³ of solution (1 mark)
      5. The solubility of sodium hydroxide in g/100g water (1 mark)
4. Study the flow chart below and answer questions that follow: 
   
   1. State one source of gas B (1 mark)
   2. Name the catalysts used in; (1 mark)
      1. Step I
      2. Step III
   3. Write chemical equations for reactions in; (2 marks)
      1. Step II
      2. Step VII
   4. Name the process that takes place in; (2 marks)
      1. Step IV
      2. Step VI
   5. Name and write the chemical formula of product X
      1. Name (1 mark)
      2. Formula (1 mark)
   6.  
      1. State one laboratory use of compound P (1 mark)
      2. Identify any other gas that can be used instead of Ammonia in step II (1 mark)
      3. State one use of gas Q (1 mark)
5.  
   1. Give the IUPAC names of the following (2 marks) 
      1.  
         
      2.  
         
   2. Describe one chemical test that you would use to distinguish between the two compounds  represented by the formulae C₂H₆O and C₂H₄O₂ (2 marks)
   3. Study the below reaction scheme to answer the questions that follows. 
      
      Identify
      1. Reagent Q …………………………………………………..(1 mark)
      2. Substance S…………………………………………………( 1 mark)
      3. Write the formula of compound P …………………………(1 mark) i
      4. Draw the structural formula of L and give its name (1 mark)
      5. Name the type of reaction, the reagent(s) and condition for the reactions in the following steps   (2 marks)
         1. Step I
         2. Step II
      6. If the relative molecular mass of U is 56000, determine the number of monomer samples n in the  polymer (2mks)
6. Below is diagram showing how hydrogen can be prepared in the laboratory and the study of the  reducing action of hydrogen 
   
   1. Define the term reduction (1 mark)
   2. Identify apparatus Q (1 mark)
   3. Identify one mistake in the set up (1 mark)
   4. Suggest a suitable drying agent M (1 mark)
   5. What is liquid Y (1 mark)
   6. Explain chemical reaction taking place in apparatus Q (1 mark)
   7.  
      1. Name liquid T (1 mark)
      2. Describe one physical test of liquid T (1 mark)
   8. Explain the role of hydrogen in the manufacture of margarine (2 marks)  
7. The diagram below shows a set-up to determine the heat of combustion of propanol. The heat produced  by burning fuel heats a known mass of water. By measuring the temperature rise of water it’s possible to approximate the value for the heat of combustion of propanol 
   
   Volume of water = 400cm³ 
   Initial temp. of water = 20^oC
   Final temp. of water = 33^oC
   Mass of propanol burnt = 0.6 g
   Specific heat capacity of water = 4.2Jg^-1k^-1 
   1. Define molar heat of combustion. (1 mark)
   2. Calculate the number of moles of propanol that burnt (C=12, H=1, O=16) (1 mark)
   3. Calculate the enthalpy change in this experiment (2 marks)
   4. Find the molar heat of combustion of propanol (2 marks)
   5. The accurate value of molar heat of combustion of propanol is -2221kJ/mol. State one error that could account for this difference (1 mark)
   6. Draw an energy level diagram showing combustion of propanol (2 marks)
   7. State two precautions taken when using a fuel (2 marks)  

MARKING SCHEME

1.  
   1.  
      1.  
         • A - Concetrated Hydrochloric acid
         • B - water
      2. Calcium oxide   Accept quick lime/CaO      rej. CaCl₂ 
      3. Absorbs unreacted/excess chlorine
      4. 2KMnO_4(s) + 16HCl(_aq) → 2KCl_(aq) + 2MnCl_2(aq) + 5Cl_2(g) + 8H₂O_(l) 
      5. Aluminium Chloride sublimes; collects further away from heating point
      6.                       Al            Cl
         Moles          0.675        1800 
                               27         24000
         Mole ratio = 0.025      0.075
                             0.025       0.025
                                1              3
         E.F is AlCl3
         n =  267  = 2
               133.5
         M.F = (AlCl₃)₂ = Al₂Cl₆ 
   2.  
      1. 6NaOH_(aq) + 3Cl_2(g) → 5NaCl_(aq) + NaClO_3(aq) + 3H₂O_(l) 
      2.  
         • Used as herbicide/ weed killer
         • Bleaching agent in paper industry
         • Chlorine bleaches by oxidation by adding [O] to the dye hence the bleaching is permanent while SO₂ bleaches by reduction by removing [O] from the dye hence temporary.   Accept equations for each.
2.  
   1. S. Smallest atomic radius making it to gain electron easily./Most electronegative/ highest electron affinity
   2. X
      1. V/Mg
      2. Q/Li. Has the smallest atomic radius hence strongest positive nuclear charge
   3. V₂X₃/Al₂S₃
   4. Covalent    rej Molecular bond
   5. S has more protons than Q leading to higher/stronger nuclear charge
   6. Bubbles/effervescence of a colourless gas. Chloride of V hydrolyses to give hydrochloric acid which reacts with the carbonate to give CO₂ 
3.   
   1.  
      1.  
      2.  
         1. 72g/100g of H₂Ot3
            showing ✓½
            correct reading  ✓½
         2. Ans a(ii) I × 1000  C₁
                   100  
              C₁   
            122.5
         3. Showing ✓½
            reading.  ✓½
            Solubility at 62°C = ^115.5g/_100g of H₂O
            42°C = 60
            Mass of crystals
            115.5 − 60      ✓½
            = 55.5g     ✓½
   2.  
      1. 25 × 0.2 = 0.005 moles
           1000
      2. Mole ratio = 1:1
         ∴ Moles of NaOH = 0.005moles       Accept for 1 without ratio
      3. If 20cm³ → 0.005
            250cm³ →  ?
         250 × 0.005
                20
         = 0.0625moles
      4. Mass = 0.0625 × 40 = 2.5g
      5. Mass of solvent = 28 − 2.5 = 25.5
         Solubility = 2.5 × 100 = ^9.804g/_100g of H₂O
                               25.5
4.  
   1.  
      • Electrolysis of brine
      • Cracking of alkanes
      • Reaction of natural gas with steam
   2.  
      1. Finely divided iron. Accept iron
      2. Platinum - rhodium/platinum
   3.  
      1. 3ZnO_(s) + 2NH_3(g) → 3Zn_(s) + N_2(g) + 3H₂O_(l) 
      2.                            heat
         2Cu(NO₃)_2(s) 2CuO_(s) + 4NO_2(g) + O_2(g) 
   4.  
      1. Neutralization
      2. Crystallization
   5.  
      1. Tetra-amine Copper(II)ion
      2. [Cu(NH₃)₄]²⁺ 
   6.  
      1. Preparation of N₂O(g)
      2. Carbon (II) Oxide/ CO Accept H₂
      3.  
         • Liquid Q used as refrigerant
         • haber process
         • in light bulbs
         • Dilutes effect of O₂ in deep sea diving
5.  
   1.  
      1. 2 - methylprop-1-ene
      2. Propanoic acid
   2. Add Na₂CO₃/NaHCO₃ into different solutions of C₂H₆O and C₂H₄O₂ in test tubes. C₂H₄O₂ produces bubbles of a colourless gas while C₂H₆O does not
   3.  
      1. Sodalime rej NaOH
      2. 2-bromoethanol or
         
      3. CH₃COOCH₂CH₃        Accept open structure
      4.  
          Tetrachloromethane.      Accept 1, 1, 1, 1 - tetrachloromethane
      5.  
         1. Type - oxidation; Reagent - H⁺/KMnO₄/H⁺/K₂Cr₂O₇ condition heat/180°C
         2. Rxn: dehyration
            Reagent: Concentrated Sulphuric (VI) acid/Al₂O₃ 
            Condition: Heat/ temp of 160°C-180°C
      6. n = 56,000 = 2,000
                   28
6.  
   1.  
      • Removal of chemically combined oxygen from a substance
      • Loss of electrons
      • Decrease/ Reduction in oxidation number
   2. Combustion tube
   3. Copper (II) Oxide is not heated
   4. Concentrated Sulphuric (VI) acid          rej CaO   CaCl_2(s) 
   5. Dilute hydrochloric acid/ Hydrochloric acid
   6. H₂ reduces CuO to Cu metal and H₂ is oxidised to water
   7.  
      1. Water 
      2.  
         • Heat to boil; b.p of 100°C
         • Determine its density; has a density of 1g/cm³ 
         • Freeze the liquid; freezes at 0°C
         • Determine its refractive index; its refractive index is 1.33158
   8. Hydrogen breaks double bond in oil to form saturated fats.
      Accept: Hardening of oils to fats 
7.   
   1. Enthalpy change that occurs when one mole of a substance is completely burnt in oxygen
   2. 0.6 = 0.01moles
       60
   3. ΔH = 400 × 4.2 × 13
      = 21840J//21.84kJ (Accept if converted) rej. ½ for j
   4. If 0.01 → 21.84kJ
      1 mole → 21.84 = − 2184kJ/mol          rej.  ½ for wrong units or sign
                        0.01
   5.  
      • Propanol and water may have evaporated
      • Incomplete combustion of Propanol.
      • Heat lost to the sorrounding not accounted for
   6.  
      
   7.  
      • Fuel storages be located away from populated areas.
      • Ensure gas taps are closed tightly after use
      • Gas cylinders should be kept away from heat
      • Charcoal stoves to be used in well ventilated rooms to curb CO poisoning.
      • Keep away from oil spills