Chemistry Paper 2 - 2021 KCSE Prediction Questions and Answers Set 1

Instructions to Candidates.

1. Answer ALL the questions in this question paper
2. Mathematical tables and silent electronic calculators may be used.
3. All working MUST be clearly shown where necessary.

1.  
   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                                                                                          (¹/₂ mk)
         2. Boilling points                                                                                          (¹/₂ mk
   2. The diagram below shows the relationship between the physical states of matter.
      
      
      1. Identify the processes B and D.                                  (2mks)
      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)
2. 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 (1v) 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)
3.  
   1. Draw and name two isomers of Pentane                                                (2mks)
   2. Study the flow diagram below and then answer the questions that follow.
      
      
      1.  Name process J, K and T                                               (3mks)
      2. State the reagents necessary for processed J and K          (1mk)
      3. Name substances  U, W, S and Y                                     (2mks)
      4. Describe how burning can distinguish CH₂CH₂ from CH₃CH₃                 (2mks)
4. 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
   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. Write down the chemical formular of the compound formed between elements K and W (1mk)
      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)
5.  
   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                     (½mk)
         2. Hydrogen gas                   (½mk)
      2. Name the following substances;
         1. Catalyst P                         (½ mk)
         2. Gas M                              (½ mk)
         3. Liquid F                           (½mk)
      3. Write the chemical equations for; formation of gas M.          (1mk)
         The reaction in the absorption tower                      (1mk)
      4. State one use of nitric (v) acid     (½mk)
6. Study the reaction scheme below and answer the questions that follow
   
   
   1. Write the chemical formular of compounds P and Q                                              (2mks)
   2. Write an ionic equation for the process that produces white precipitate P               (1mk)
   3. Name process 2                                                                                                (1mk)
   4. Name the process that separated P and Q                                                           (1mk)
   5. Write a balanced chemical equation for the formation of white precipitate L.         (1mk)
   6. State the condition required for process 3                                                           (1mk)
   7. What physical process is exhibited in process 3                                                  (1mk)
   8. Name the anion present in colourless solution Z                                                  (1mk)
   9. Write the formula of the complex ion present in colourless solution Y                     (1mk)
7. 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)
8. In an experiment, 40cm³ of 0.1 M sodium hydroxide solution was placed in a suitable apparatus and 5.0cm³ portions of hydrochloric acid were added. The resulting mixture was stirred with a thermometer and the temperature taken after each addition. Both solutions were initially at 20⁰c
   1.  
      1. Plot a graph of temperature against volume of the acid added                                   (4mks)
      2. Use the graph to determine the concentration in moles per litre of the hydrochloric acid                                                                                                                             (2mks)
   2.  
      1. Calculate the heat change for the reaction                                                         (1½mk)
      2. Molar enthalpy of neutralization of hydrochloric acid by sodium hyndroxide solution (density of solution 1g/cm³ specific heat capacity 4.2 kj/kg)     (1½mks)
      3. Draw an energy level diagram for the reaction (1mk)
      4. Write the thermochemical equation for the reaction                                           (1mks)                                 

MARKING SCHEME

1.  
   1. 1. Q √1
         Sharp/ constant melting point and boiling point.
      2. Melting point – lower the M.P √ ½
         Boiling point – raises the b.p√ ½
   2. 1. B – Melting √
         D - Condensation√1
      2. Sublimation √1
      3. Iodine √ ½
         Ammonium chloride √ ½                Any two 1mk.
         Solid ice √ ½
         Iron (III) chloride√
         Aluminum chloride √ ½
      4. Exothermic √ ½
         Involves heat loss ½

2.  
   1. Nitrogen gas√ 1
   2. 1. Carbon (iv) oxide gas√1
      2. Oxygen gas√1
      3. Nitrogen√1
   3. To remove/absorb water vapour or dry / drying agent.
   4. 1. 2 NaOH_(Aq) +CO_2(g) → Na₂CO_3(S)+H₂O _(L)√1
      2. 3Mg _(s) +N_{2 (g)}                             Mg₃N_2(S)√1
         Penalize ½ if state symbols miss/wrong
         Penalize fully if not balanced.
   5. Brown solid changes to black√1
      Brown copper metal oxidized/ reacts with oxygen to form copper (II) oxide (black)
   6. - Argon
      - Neon                 Any one. (1mk)
      - Helium
3.  
   1.  
      
   2. 1. J- Hydrogenation√1
         K –Bromination/Halogenation √1
         T-Polymerisation√1
      2. J-Hydrogen gas √ ½
         K- Bromine gas √ ½
      3. U-carbon (IV) Oxides gas √1
         W – 1- chloroethane √ ½
         S – Polyethene√ ½
         Y – Sodium propanoate√ ½
   3. CH₂CH₂ √ 1   burns with a yellow sooty flame while CH₃CH₃ √1 burns with a blue non- sooty flame.
4.  
   1. C and T (Mark tied to the two elements)
   2. J – has five energy levels/ highest number of energy levels.
   3. 
   4. Y -2,8,8,2 √ 1
      w – 2,8,7√1
   5. Period 3       should be shown on the grid
      Group 5           otherwise penalize fully
   6. M √
   7. KW₂
      
   8. 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.
5.  
   1.  
      1.                          _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. Sodium nitrate√ ½
         Sodium nitrate √ ½
      3. Charcoal glow red hot √1
      4. To absorb Carbon (IV) oxide gas formed√1
      5. Carbon (II) oxide gas √1
         
         
   2.  
      1. Nitrogen gas – fractional distillation of liquid air
         Hydrogen gas – Electrolysis of brines
         Cracking of hydrocarbon
         Water gas
      2. Catalyst P platinum/ platinum – rhodium √ ½
         Gas M – Nitrogen (II) Oxide √ ½
         Liquid   F – water √ ½
                           _Platinum
      3. 4NH₃ +5O₂     →     4NO_(g) + 6H ₂O (₁₎
         4 NO_{2 (g)} +2H₂O_(l)+O_2(g)  →  4 HNO_3(aq)
      4.  Manufacture of nitrate fertilizers, synthetic fibre, dyes, drugs, explosives,
         Purification of metals                                                                                               (Any one ½ mk).

6.  
   1. 1. P -     PbSO4     NOTE penalize the name fully
      2. Q – Na₂ NO₃
   2. Pb²⁺ _(aq) + S04^2- _(aq)   → PbSO4_(s)
   3. Double decompositions/ precipitation
   4. Filtration
   5. Pb(NO₃)_{2 (aq)} + 2HCl_(aq) → Pbcl_{2 (s)} + 2HNO_{3 (aq)}
   6. warming
   7. solubility
   8. chloride    
   9. Pb(OH)₄ ^2-

7.  
   1.  
      1. solid W – Sodium sulphite
      2. Dropping funnel
   2. Drying agent    
   3.  
      
   4. Yellow iron (III) sulphate solution √1 turned pale green sulphur (IV) oxide gas reduced iron (III) ions to iron (II) ions√1.
   5. Na₂SO_3(S) + 2Hcl_(aq) → 2 Nacl_(aq)+SO_2(g) + H₂O_(l)
      moles of HCl 
      2 moles   → 1000 cm³
            ?      →  50 cm³              √ (1 mk)
      2×50 = 0.1 moles
      1000
      
      Mole ratio HCl : SO₂
                      2   : 1 √ ½
      Moles of SO_{2 =} ¹/₂= 0.05moles
      1 mole  → 24dm³ 
      0.05 moles → ?
      0.05 × 24 = 1.2 dm³√ ½
              1
      
      
8.  
   1.  
      1.  
         
      2. Volume (shown on the graph) =36.5 cm³√ ½
         Mole ratio.
         
   2.  
      1.  
         
      2.  
         
      3.  
              
      4.