Chemistry Paper 2 Questions and Answers - Lainaku II Joint Mock Examination 2023

Instructions to candidates

• Answer all the questions 
• Non-programmable silent electronic calculators and KNEC mathematical tables may be used.
• All working must be clearly shown where necessary.
• Candidates should answer the questions in English.

1.  
   1. Detergents are substances that improves cleansing properties of what. Name two substances that are added to detergents to make them more effective in cleansings. (1mark)
   2. The flow chart below shows steps in the manufacture of soapless detergent. Study it and answer the questions that follow.
      
      1. State the condition necessary for Step I. (1mark)
      2. Write an equation for the reaction in step I (benzene, C₆H₆ is represented as ). (1 mark)
   3.  
      1. Name the process in step III. (1mark)
      2. Give the reagent in step III. (1mark)
      3. Give the name of the product of step III. (1mark)
   4. Explain:
      1. One advantage of soapless detergents over soaps. (1mark)
      2. One disadvantage of soapless detergents over soaps. (1mark)
   5. Pentanoic acid reacts with butan-1-ol to form an organic compound.
      1. What is the name given to the above type of reaction? (1mark)
      2. A certain catalyst must be added to the mixture to increase the rate of reaction.
         Name the catalyst. (1mark)
         Explain the role of the catalyst in the above reaction. (1 mark)
2. Study the structure below and use it to answer the questions that follows
   
   1. State two observations made when the molecule is heated to a temperature of 113°c. (2 marks)
   2. Write an equation of the reaction between sulphur atom with hydrogen gas. (1mark)
   3. Below is a flow chart. Use it to answer the questions that follow.
      
      Name: (2 marks)
      1. Gas Q
      2. Gas B
   4.  
      1. State the observations made in step I. (2marks)
      2. Step I and Step II occur in the Contact process. State the optimum conditions necessary for Step II to occur. (2marks)
      3. Name the reagent used in Step IV. (1 mark)
      4. Explain why water is not used in Step III. (1 mark)
   5. Sulphur (iv) oxide is a major environmental pollutant and should not be emitted into the atmosphere. Name the reagent used to achieve this. (1 mark)
   6. Explain the role of Sulphur in vulcanization of rubber. (1 mark)
3. Study the Standard electrode potential for the half-cell given below and use it to answer the questions that follow. The letters do not represent the actual symbols of elements.
                                                                                  E0 (volts)
   

   P+ (aq) + e- → P(s)	-2.92
   Q+ (aq) + e- → Q (s)	+0.52
   R+ (aq)+ e- → ½R2 (g)	0.00
   S2+(aq) + 2e- → S(s)	-0.44
   ½T2 (g) + e- → T-(aq)	+1.36

   
   
   1. Identify the strongest oxidizing agent. Give a reason for your answer. (2 marks)
   2. Which half cells would produce the highest potential difference when combined? (1 mark)
   3. Predict whether the reaction represented below can take place. (2 marks)
      S_(s) + P⁺_(aq) → S²⁺_(aq) + P_(s)
   4. Write a cell representation for the cell that would be constructed by combining P and Q. (2 marks)
   5. 100 cm³ of 2M sulphuric acid was electrolyzed using the set up represented by the following diagram.
      
      1. Write an equation for the reaction that produces gas B.
      2. Describe how gas A can be identified. (1 mark)
      3. Explain the differences in the volumes of gases produced at the electrodes. (2 marks)
      4. An electric current is passed through a solution for 18 minutes. The volume of gas produced at the cathode is 480 cm³.Calculate the current used. (Molar gas volume at rtp = 24 dm³ IF = 96500C)  (2 marks)
4. In an experiment, dry hydrogen chloride gas was passed through heated iron wool as shown in the diagram below. The gas produced was then passed through heated lead (II) oxide.
    
   1.  
      1. State the function of water in the flask. (1 mark)
      2. Write the equation for the reactions that took place in tubes labeled A and B. (2 marks)
         Tube A
         Tube B
      3. Explain how the total mass of tube B and its contents would compare before and after the experiment. (2 marks)
   2. Chlorine gas and hydrogen chloride gas can be prepared using the following reagents: sodium chloride, concentrated Sulphuric (VI) acid and potassium manganate (VII) and hydrochloric acid.
      1. State the role of each of the following in the reaction. (1 mark)
         Concentrated Sulphuric (vi) acid
         Potassium manganate VII. (1 mark)
      2. Name the bleaching agent formed when chlorine gas is passed through cold dilute sodium hydroxide solution. (1 mark)
      3. Apart from bleaching action, state the other use of compound formed in (ii) above. (1 mark)
   3. 1.9 g of magnesium chloride were dissolved in water. Silver nitrate solution was then added until in excess. Calculate the mass of AgNO₃ that was needed for the complete reaction. (2 marks)  (Ag = 108, O = 16, N = 1, Mg = 24, Cl = 35.5)
5. Use the grid below to answer the questions that follow (the letters do not represent the actual symbols of the elements)
   
   1. Give the family name to which elements in the shaded area belong. (1 mark)
   2. State and explain the difference in reactivity between G and J. (2 marks)
   3. How does the atomic radius of K compare to that of L? Explain. (2 marks)
   4. Element R forms an oxide of formula RO₂ and it belongs to period 2. Indicate on the grid the position of R. (1mark)
   5. Give the formula of the compound formed between K and P. (1mark)
   6. Give the type of bond formed when F reacts with O. Explain. (2 marks)
   7. Give the electronic arrangements of the ions of G and M. (1mark)
      G
      M
   8. Element A can fit in two groups. Name the two groups and explain. (2 marks)
6. An experiment was carried out using the apparatus as shown below to prepare a sample of nitrogen gas from air.
   
   1. Identify one mistake in the setup. (1mark)
   2. Name what is contained in: (2marks)
      1. Bottle A ……………………………………………..
      2. Tube B ………………………………
   3. The nitrogen prepared by his method is denser than nitrogen prepared by fractional distillation of liquid air. Explain. (1mark)
   4. Use the flow diagram to answer the questions
      
      1. Give the formulae of three gases which can reduce hot copper (II) oxide. (3 marks)
      2. Explain what will be observed when the above reaction takes place. (1 mark)
   5. In the Haber process, the optimum yield of ammonia is obtained when a temperature of 450°c,a pressure of 200 atmospheres and an iron catalyst are used.
      
      How is the yield of ammonia affected if the temperature is raised to 600o C. Give a reason? (2marks)
7. The flow chart below illustrates extraction of Zinc from zinc blende. Study it and answer the questions that follow
   
   1. Give an equation for the reaction in roasting furnace. (1 mark)
   2. Name each of the substances marked L and N. (2 marks)
   3. Why is it necessary to condense substance N? (1 mark)
   4. Which other factory can be set up near the zinc extraction plant. Explain. (2marks)
   5. Give one use of zinc metal. (1 mark)
   6.  
      1. Zinc sulphide and sulphuric acid react according to the following equation.:
         ZnS_(s) H₂SO₄ → ZnSO_4(aq) + H₂S(g)
         2.91g of zinc sulphide reacted with 100cm³ of 0.2M Sulphuric acid. Determine the reagent that was in excess. (Zn = 65.0, S = 32.0). (2 marks)
      2. Calculate the volume of hydrogen sulphide H₂S ) gas produced in the reaction above at rtp.
         Molar gas volume 24 dm³) (2 marks)

MARKING SCHEME

1.  
   1.  
      • colors/dyes
      • perfumes/ esters 2x½ =1mk
      • stabilizers
      • tetraoxophosphate
   2.  
      1. Heating.
      2. 
   3.  
      1. Neutralization
      2. Sodium hydroxide
      3. Sodium dodecene benzene sulphonate/ sodium alkylbenze sulphonate 1mk
   4.  
      1. Soapless detergent form compounds salts of calcium and magnesium hence do not form scum with hard water.
      2. The active ingredients, such as benzene sulphonate are non-biodegradable and they hence accumulate and end up in the bodies of organism.
   5.  
      1. Esterification
      2. Conc. Sulphuric acid
   6. It absorbs the molecules of water formed during the reaction hence forward reaction proceeds to produce water to replace the amount withdrawn.1mk
2.  
   1.  
      • Solid melts 1mk
      • Forms a clear an amber liquid.1mk
   2. H_2(g) + S_(s) → H₂S_(g) 1mk
   3.  
      1. Hydrogen sulphide 1mk
      2. Sulphur (IV) oxide 1mk
   4.  
      1.  
         • Blue flame 1mk
         • chocking smell.
      2.  
         • Temp 450°c
         • 2 to 3 atmospheres ( specific pressure in the range)
         • V₂O₅ or Platinum catalyst
      3. Carbon (iv) sulphide
      4. A vigorous reaction that produces dangerous poisonous acid mist.
   5. Ca(OH)_2(aq) + SO_2(g) → CaSO_3(ag) + H₂O₍₁₎
   6.  It makes the rubber tougher/ less flexible / less soft by reducing the number of double bonds.
3.  
   1. T₂ has the highest electron affinity or it is the most electropositive.
   2. P and T or P(s)/ P⁺ (aq)//T^-(aq)/½T2(g)
   3. S(s) + P⁺_(aq) S²⁺_(aq) + P_(s)
      Solution:
      S(s)/S²⁺(aq)//P⁺(aq)/P(s)
      E.m.f    = E red − E oxid
                   = (−2.92) – (−0.44 )
                   = − 2.48v
      Hence the voltage is –ve and therefore reaction cannot take place.
   4. P(s)|P+(aq) // Q+(aq)| Q(s) = +3.44V 1mk
      1mk for calculating the emf (+3.44v)
   5.  
      1. 4OH⁻_(aq) 2H₂O_(l) + O₂(g) + 4e^-
      2. Introduce a burning wooden splint at the mouth of gas jar filled with a gas A. The gas extinguishes a burning splint with a pop sound.
      3. 2moles of gas A are produced at cathode while only 1 mole of gas B is produced at the anode by the same quantity of electricity. WTTE
   6. Q = It
      24000 cm³ = (2 × 96500) C
      480 cm³ = ?
                    = 2 × 96500 × 480
                               24000
                    = 3860C
      Q = It but Q = 3860C
      3860C = I × 18× 60
      I =  3860C
           18 × 60
                = 3.57 A
4.  
   1.  
      1. Water is used to remove excess fumes or unreacted fumes of hydrogen chloride gas.
      2. A; 2HCl_(g) + Fe_(s) → FeCl_2(aq) + H_2(g)
         B; PbO_(s) + H_2(g) → Pb(s) + H₂O_(g)
      3. Total mass would be lower at the end of the experiment because PbO is reduced to form lead (Pb) and steam (H₂O) which escapes air.
   2.  
      1.  
         • Conc.Sulphuric acid
         • Conc. H₂SO₄ reacts with NaCl to produce HCL(g)
         • Pottasium manganate (VII).
         • Used to oxidise HCL_(g) to Cl2 _(g)
      2. NaOCl – Sodium hypochlorite
      3. Use to kill germs or as a disinfectant
   3. MgCl_2(aq) + 2AgNO_3(aq) → Mg(NO₃)_2(aq) + 2AgCl_(s)
         Mole ratio MgCl₂ : AgNO₃
                                  1 : 2
        Moles of MgCl2 = 1.9 = 0.02
                                      95
        Moles of AgNO₃ = 0.02 × 2 = 0.04 Moles
        R.F.M of AgNO₃ = 170
        Mass of AgNO₃ = moles × R.F.M
                                  = 0.04 × 170
                                  = 6.8 g
5.  
   1. Transition elements
   2.  
      • G is more reactive than J
      • G requires less energy to lose its one outer electron than 2 electrons for j
   3. K has a larger atomic radius than L.K has less effective nuclear attraction which makes its radius to be larger than that of L.
   4.   
      
   5. KP₃
   6. Ionic bond; F (metal) transfers electrons to O (non metal).
   7. G: 2.8 ; M: 2.8
   8.  
      •  Can lose one electron in its outer energy level like members of group 1 to be stable
      • Can gain one electron to be stable like members of group VII.
6.  
   1. The tube bringing in air should be dipped inside the solution in bottle .
   2.  
      1. A; NaOH solution
      2. Tube B : Copper metal
   3. The nitrogen prepared has impurities which make it denser.
   4.  
      1. CO , NH₃, H₂
      2.  Black solid will turn re-brownish; copper (II) oxide will have been reduced to copper.
   5. The yield is reduced since the reaction is exothermic. Increase in temperature favours backward reaction.
7.  
   1. 2ZnS_(s) + 3O2_(g) → 2ZnO_(s) + 2SO_2(g)
   2. L: Sulphuric (IV) oxide N : Zinc vapour
   3. It produced in vapour state/form.
   4. Sulphuric (VI) acid manufacturing plant.
      To utilize the sulphur (IV) oxide by product. *Any industry that uses SO₂ as raw material
   5.  
      • Galvanization of iron sheets to prevent corrosion/rusting.
      • Making brass, an alloy of copper and zinc.
      • Making outer casing of dry batteries.
      • Zinc cyanide is used for refining silver and gold.
   6.  
      1. R.F.M ZnS = 97                       Sulphuric acid H₂SO₄
         Moles 2.91= 0.03 moles           0.2 mole = 1000cm³
                     97                                 ? = 100cm³
                                                       100 × 0.2 = 0.02 mole
                                                             1000
          Zinc sulphide is excess.
      2. 0.02 mole × 24000 = 480cm³