CHEMISTRY PAPER 2 - KCSE 2019 STAREHE PRE MOCK EXAMINATION (WITH MARKING SCHEME)

QUESTIONS

1.  
   1. The diagram below shows a set-up used to separate solid K and liquid R
      
      
      1. What name is given to the method of separation shown above                   [1mk]
      2. What physical property of solid K makes it possible to separate from the mixture as shown above      [1mk]
      3. State one example of a mixture that can be separated as shown above            [2mks]
      4. Name one other method that can be used to separate the mixture of K and L [1mk]
      5. Identify apparatus A and B                                                                          [2mks]
      6. State two other possible uses of apparatus A, other than the one shown on the diagram     [2mks]
   2. The diagram below shows part of a set-up used to investigate the effect of heating copper(II) sulphate crystals
      
      
      1. State two likely observations made in apparatus D                                               [2mks]
      2. Identify substance F                                                                                                 [1mk]
      3. Was the change undergone by the copper {II} sulphate crystals temporary chemical change or permanent chemical change? Explain your answer  [2mks]

2. In an experiment to determine the enthalpy of displacement when zinc is heated with copper (II)Sulphate, excess zinc powder was added to 125cm³ of 0.75M copper {II} Sulphate solution in a beaker. The temperature of the mixture changed from 24⁰Cto 29⁰C. Assuming that the density of the solution was 1g/cm³ and its specific heat capacity was 4.2KJK^-1K
   
   1. Write a chemical equation of the reaction that occurred                                              [1mk]
   2. Why was it necessary to use excess zinc powder                                                         [1mk]
   3. State and explain one observation made by the end of the experiment                       [2mks]
   4. Determine the enthalpy change in the reaction that occurred                                         [3mks]
   5. Determine the molar enthalpy of displacement of copper (II) ions by zinc                 [3mks]
   6. Represent the reaction on an energy level diagram                                                     [2mks]

3. Study the diagram below and answer the questions that follow;
   
   
   1. Identify the following        [4mks]
      1. Substance M
      2. Solid P
      3. Gas R
      4. Solution L
   2. Write the ionic equation of the reaction occurring at step
      1. Step 2     [1mk]
      2. Step 3
   3.  
      1. State the observation made when ammonia solution is added to lead {II} nitrate solution drop wise till excess      [2mks]
      2. The equation below shows a reversible reaction
         H₃O⁺_(aq) + HSO^4- _(aq)  →H₂O_[l] + H₂SO_4[aq]
   4. Identify the acid in the fowards reaction                                                                         [1mk]
   5. Identify the base in the reverse reaction                                                                           [1mk]

4. The diagram below shows a set-up used to investigate the reaction of magnesium and steam
   
   
   1. Identify gas X                                                                                                                [1mk]
   2. Write a chemical equation of the reaction;
      1. Occurring in the glass tube            [1mk]
      2. Leading to the flame of the burning gas X  [1mk]
   3. Explain why it was necessary to;
      1. Polish the magnesium ribbon         [1mk]
      2. Heat the wet sand before heating the magnesium ribbon                                     [1mk]
   4. Identify apparatus J          [1mk]
   5. How does the mass of the magnesium compare before and after the experiment. Explain.[2mks]
   6. State two physical properties of gas X            [2mks]
   7. State two uses of gas X            [2mks]
   8. State the role of the wet sand        [1mk]

5. The diagram below shows a flow chart representing process used in the industrial manufacture of hydrochloric acid
   
   
   1. Identify gas R            [1mk]
   2. Write a chemical equation for the reaction between gas R and chlorine gas               [1mk]
   3. State one possible role of the glass beads                   [1mk]
   4. State one possible source of;
      1. Gas R                         [1mk]
      2. Chlorine gas              [1mk]
   5. Explain why it’s necessary to allow only small amount of gas R to burn in excess chlorine gas in the above process           [1mk]
   6. State two uses of hydrochloric acid                                                                           [2mks]
   7. Describe a confirmatory test for hydrogen chloride gas                                             [2mks]
6.  
   1. Name the following hydrocarbon                                                                               [3mks]
      1. CH₃CH₂CH₃
      2. CH₃CHCHCH₃              
      3. CH₃CHCHCH₂CH₂Br
   2. Study the reaction below;
      CH₂CH₂ + HBr  → substance T
      1. Name substance T     [1mk]
      2. Draw the structural formulae of substance T         [1mk]
      3. Draw the structural formulae and name the compound that would be formed if chlorine gas was used in place of HBr      [1mk]
   3. State one domestic use of ethane                                                                                [1mk]
   4. State two natural sources of alkanes                                                                             [2mks]

7. The grid below show a section of the periodic table. The letters are not the actual chemical symbols"
   
   
   1. Which letter represents the
      1. Most reactive non metal. Explain your answer                                                          [2mks]
      2. Most reactive metal. Explain your answer                                                     [2mks]
   2. What name is given to the family into which element E belongs                                [1mk]
   3. Write the formulae of the compound formed between
      1. F and G                    [1mk]
      2. K and oxygen            [1mk]
   4. How does the atomic radius of F and G compare? Explain                                                    [2mks]
   5. In terms of structure and bonding, explain why the oxide of F has a high melting point     [2mks]
   6. State one possible use of
      1. Element J                                                                                                                   [1mk]
      2. Element E                                                                                                                    [1mk]

MARKING SCHEME

1.  
   1.  
      1. filtration   √1
      2. its insoluble in Liquid L     √1
      3. sand √1 and water   √1
         Both must be correct
      4. Decantation√1
      5. Apparatus A- filter funnel   √1
         Apparatus B – conical flask √1
      6. used to deliver solution/ liquids carefully to apparatus with narrow necks.   √1
         Can be used in dissolving highly soluble gases in water to avoid sucking back effects√1
   2.  
      1. Blue hydrated copper(ii) sulphate turns to white powder
         Colourless liquid droplets on the cooler parts of the test tube √1
      2. water   √1
      3. temporary chemical change √1 because change can be reversed√1

2.  
   1. Zn_(s) + CuSO_4(aq)  →ZnSO_4(aq)   + CU_(s)√1
   2. To ensure all the copper(ii) sulphate solution was used up     √1
   3. Blue colour of copper(ii) solution fades√1 because copper(ii) ions responsible for the colour are displaced from the solution√1
      Brown solid is deposited √1 because copper(ii) ions are reduced to copper metal which is a brown solid.   √1
   4.  
      
   5.  
       
   6.  
      

3.  
   1.  
      1. substance M- lead (ii) hydroxide/ pb(OH)₂
      2. solid P- lead(ii) carbonate/ PbCO₃
      3. gas R- carbon (iv) oxide   √1
      4. Solution L- Nitric (v) acid   √1
   2.  
      1. Pb(OH)_2(s)   +   2OH^-→ [Pb(OH)₄]^2-_(aq) √1
      2. Pb²⁺⁽_aq)    +   SO^2-_4(aq) → PbSO_4(s)   √1
   3.  
      1. forms white ppt √1 insoluble in √1 excess ammonia
      2. H₃^O+     √1
      3. H₂O(l)

4.  
   1. hydrogen gas
   2.  
      1. Mg_(s) + H2O(l)→ MgO_(s) +H_2(g) √1
      2. H_2(g)     +   O_2(g)  →H₂O_(l)   √1
   3. to drive out air that was initially in the glass tube so that it does oxidise the magnesium ribbon.   √1
   4. clamp and stand √1
   5. mass of magnesium increases√1 because magnesium react with oxygen ,to form magnesium oxide powder. √1
   6. -less dense than air     √1
      -insoluble in water √1
      -colourless and oudourless gas √1
      Any two correct
   7. -used in haber process to manufacture ammonia gas
      -used in hardening of margarine(oil)
      Any two correct
   8. to generate steam that would react with magnesium ribbon.   √1

5.  
   1. hydrogen gas √1
   2. H_2(g) +     Cl_2(g)  →2HCl_(g)   √1
   3. to increase the surface area over which the gas dissolves in water √1
   4.  
      1. Electrolysis of brine
         Cracking of long chain hydrocarbons
         Any one correct
      2. Electrolysis of fused sodium chloride or brine     √1
   5. to prevent explosion when chlorine reacts with hydrogen.   √1
   6. removing mist from metal   √1
      Making of dyes and drugs   √1
   7. open a bottle of concentrated ammonia√1and place it near hydrogen chloride gas, dense white fumes of NH₄Cl are observed

6.  
   1.  
      1. propane   √1
      2. But-2-ene   √1
      3. 5- bromo pent- 2- ene √1
   2.  
      1. Bromo ethane   √1
      2.  
          
      3.  
         
   3. used as a fuel. √1
   4. natural gas√1
      Biogas   √1
      Crude oil √1
      Any two correct

7.  
   1.  
      1. D- its most electronegative       √1
      2. K- its most electropositive     √1
   2. Alkaline earth metals √1
   3.  
      1. F₂G₃   √1
         Accept Al₂O₃
      2. K₂O   √1
   4. F is larger than G√1. G has higher nuclear charge hence electrons are pulled inwards more strongly.   √1
   5. has giant ionic structure with strong ionic bonds. √1
   6.  
      1. its used in light bulbs to provide an inert environment to prevent oxidation. √1
         Used as an insulator in arch welding   √1
         Any correct
      2. used in manufacture of magnesium hydroxide which is used as anti-acid medicine
         Its low density alloy with aluminum is used in airplane construction
         Any correct