Chemistry Paper 2 Questions and Answers - Sukellemo Joint Mock Examinations July 2020

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INSTRUCTIONS TO THE CANDIDATES: 

  • Write your name and index number in the spaces provided above
  • Sign and write the date of examination in the spaces provided.
  • Answer all the questions in the spaces provided. 
  • All working must be clearly shown where necessary.
  • Mathematical tables and electronic calculators can be used.

For Examiners Use Only

Question  Maximum score  Candidate's score 
 1  10  
 2  13  
 3  12  
 4  13  
 5  11  
 6  11  
 7  10  
Total  80  


QUESTIONS

1.

  1. The figure shows the extraction of Aluminium from bauxite.
    Q1 JGAYGD
    1. Write the formula of bauxite (1mrk)
    2. How is the ore (bauxite) concentrated before it is electrolyzed? (1mk)
    3. Identify;
      1. Product A (1mk)
      2. Electrolyte B (1 mk)
      3. Material used to make electrode C (1mk)
  2. What is the purpose of dissolving electrolyte B in molten cryolite (Na3AlF6) (1mk)
  3. Explain why anode has to be replaced from time to time. (1 mk)
  4. Write the equation for the chemical reaction that take place when aluminium reacts with Iron (III) Oxide. (1mk)
  5. State any two uses of Aluminium. (2mks)

2.

  1. Give the systematic names for following compounds;
    1. CH3CH2CH2CH2OH (1mk)
    2.  Q2 JHGAGDA (1mk)
    3. CH3CH2CH3  (1mk)
  2. Study the flow chart below and use it to answer the questions that follow
    Q2 B JMHGBUYAGD
    1. Name:
      Substance A(1mk)
      Process 1(1mk)
      Substance B(1mk)
      Gas C(1mk)
      Substance D (1mk)
      Compound E(1mk)
    2. Identify the type of Polymerization that results to the formation of compound E (1mk)
    3. If one mole of sugar, C6H12O6 produces two moles of pure ethanol, C2H5OH and two moles of carbon (IV) oxide gas as the only product; 
      1. Write an equation for the reaction (1mk)
      2. If 144kg of sugar (C6H12O6) was used to produce ethanol in this process, calculate the mass in kg of ethanol produced (C=12, H=1, 0=16) (2mks)

3. The grid below shows a section of the periodic table. The letters are not the actual chemical symbols
Q3 KJHAUKHDA

  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 (1/2mk)
    2. K and oxygen (1/2mk)
  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 (1 mk)
    2. Element E (1mk)

4. Study the scheme below and answer the questions that follow 
q4 jhyguygayud

  1. Name the following Gas W (3mks)
    Gas W   Product R   
    liquid K    Compound C  
    Gas Z   Compound H which is a double salt  
  2. Name the catalysts used in chambers. (3mks)
    A.........................................
    B.........................................
    C.........................................
  3. Write balanced equations for the following (2mks)
    1. reaction in catalytic chamber B
    2. formation of Liquid K
  4. Explain why it is not advisable to dissolve the product of chamber C in water. (1mk)
  5. Calculate the mass of compound A formed if 472.5kgs of product Rare reacted with excess ammonia to prepare it.
    (S=32, 0-16, H-1, N=14) (3mks)
  6. Give one use of Sulphuric (VI) acid. (1mk)

5. In an experiment to determine the enthalpy of displacement when zinc is heated with copper (11) 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 24°C to 29°C. Assuming that the density of the solution was 1g/cm' and its specific heat capacity was 4.2 kJKg-1K-1 

  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 molar enthalpy change in the reaction that occurred (3mks)
  5. State Hess's Law. (1mk)
  6. Given that:
    C(s) + O2(g) → CO2(g)   △H = -393 kJ/mol
    H2(g) + 1/202(g) → H20(l)   △H = -286 kJ/mol
    C2H2(g) + 5/2O2(g) → 2CO2(g) + H20(l)   △H = -2599 kJ/mol
    Using an energy cycle diagram calculate the enthalpy of formation of ethyne from its constituent elements. (3mks)

6. Standard electrode potentials for half-cell reactions are shown below

A2+ (aq) + 2e- → A(s) -0.76V
B2+ (aq) +2e- → B(s) -0.13V
C(aq) +e- → C(s) +0.08V
D2+ (aq) +2e- → D(s) +0.34V

The cell below was set-up using A and B electrode
q6 hgaytd

  1.  Give the half-cell equation for each half cell (2mks)
  2. Write the overall cell equation (1mk)
  3. Calculate the e.m.f of the cell above (1mk)
  4. Describe how the salt bridge helps in maintaining the charge balance in each half cell when the cell is in operation (2mks)
  5. It is not advisable to use potassium chloride salt bridge when lead II nitrate solution is used as an electrolyte in the above set-up. Explain. (2mks)
    1. State Faraday's law of electrolysis (1mk)
    2. 9.67g of a metal M was deposited by a current of 10 A within one and half hours. Work out the formula of the ions of metal M, given that the R.A.M of Mis 52, and IF = 96,500 C (2mks)

7. The table below contains information from measurements made to the radioactivity counts per minute from radio isotope iodine- 128.

Counts per minute  240  186  170  156  143  122  108
Time (minutes)  0  15  20  25  30  40  50
  1. On the grid provided, plot a graph of counts per minute against time. (3mks)
    q7 ujgjsd
    Use the graph to determine the half-life of iodine - 128 (1mk)
  2. What is the count rate after: (2mks)
    1. 12 minutes
    2. 22 minutes
  3. Iodine 128 has atomic number 53. It under goes nuclear radiation by emitting two alpha particles and one beta particle. Calculate the mass number and atomic number of the daughter nuclide: (2mks)
    Mass number:
    Atomic Number:
  4. State two uses of radioactive isotopes in agriculture. (2mks)




MARKING SCHEME

1.

  1.                                
    1. Write the formula of bauxite
      • Al203.2H2O
    2. How is the ore (bauxite) concentrated before it is electrolyzed?
      • The ore is ground and treated under pressure with concentrated NaOH/ KOH 
    3. Identify
      1. Product A
        • Molten aluminium
      2. Electrolyte B
        • Molten aluminium oxide
      3. Material used to make electrode C
        • Carbon or graphite 
  2. What is the purpose of dissolving electrolyte B in molten cryorite
    • To lower the melting point of Al203
  3. Explain why anode has to be replaced from time to time
    • It reacts with oxygen to form CO2
  4. Write equation for chemical reaction when aluminium reacts with iron (III) oxide
    • Al(s) + Fe2O3(s) →  Al203(s)+ Fe(s)
  5. State any two uses of aluminium
    • Used to make cooking pans/ sufurias
    • Used to make electric cables
    • Used in making parts of aeroplanes

2.

  1. Give systematic names for the following compounds
    1. Butan-1-ol 
    2. Ethylpropanoate
    3. Propane 
  2.                            
    1. Name
      • Substance A-Yeast (zymase enzyme)
      • Process I Fractional Distillation 
      • Substance B-Sodium ethoxide
      • Gas C-Hydrogen
      • Substance D- Ethene
      • Compound E-Polyethene
    2. Identify type of polymerization that results to the formation of compound E 
      • Addition 
    3.                                    
      1. Write an equation of the reaction
        • C6H12O6(s) → 2C2H5OH(l) + 2CO2(g)
      2. calculate mass in kg of ethanol produced
        • 144 x 1000-144000g
          Moles =             144000            
                       (12x6) + 12 + (6 x 16)
          = 144000
                 180
          = 800moles
          MR 1:2
            800: X
          800 x 2
              1
          = 1600moles
          Mass = 1600 x (12 x 20 + 6 + 16)
          = 1600 x 46 =  73600g
          73.6kg

3.

  1. Which letter represents
    1. most reactive non-metal, explain
      • D-readily gains electrons/most electromagnetic
    2. Most reactive metal. Explain
      • K-Readily loses electrons most electropositive
  2. What name is given to the family into which element E belongs
    • Alkaline earth metals
  3. Write formulae of compound formed between
    1. F and G
      • F2G3
    2. K and oxygen 
      • K2O
  4. how does the atomic radius of F and G compare. Explain
    • F has larger atomic radius than G. G has more protons hence stronger nuclear force of attraction pulling electrons closer to the nucleus. 
  5. In terms of structure and bonding, explain why the oxide of F has a high melting point 
    • It has a giant ionic structure with strong ionic bonds that require a lot of energy to weaken. 
  6. state one possible use of
    1. Element J 
      • Used in lighting bulbs 
    2. Element E
      • Used in flashlight photography 
      • Used as reducing agent in production of titanium
      • Used to manufacture Mg(OH)2 anti-acid

4. 

  1. Name the following
    Gas W  Nitrogen (II) oxide  Product R Concentrated Sulphuric (VI) acid
    Liquid K Oleum Compound C Ammonium Nitrate
    Gas Z Hydrogen Compound H which is a double salt  Hydrated ammonium Iron (II) sulphate
  2. Name catalysts used in chambers
    • A-Tron (finely divided) 
    • B-Platinum-Rhodium
    • C-Vanadium (V) oxide or platinum
  3. write balanced equations for the following
    1. reaction in catalytic chamber B
      • 4NH3(g) + 5O2(g)  → 4NO(g) + 6H2O(g) 
    2. Formation of liquid K
      • SO3(g) + H2SO4(l) → H2S2O2(2)
  4. Explain why it is not advisable to dissolve the product of chamber C in water
    • It will form acid sprayf mist that is dangerous to factory workers.
  5. Calculate mass of compound A formed if 472.5kg of product Rare reacted with excess ammonia to prepare it
    • 2NH3 + H2SO4  →  (NH4)2SO4
      RFM H2SO4 = 2 + 32 + 64 = 98
      Moles = 472500g
                       98
      = 4821.4 moles
      MR 1:1 therefore 4821.4 moles of (NH4)4SO4
      RFM (NH4)2SO4 = (2 x 14) + 8 + 32 + 64 = 132
      1 mole = 132g
      4821.4 moles = 4821.4 x 132
                                         1
      = 636424.8g or 636.4248kg
  6. Give one use of sulphuric (I) acid
    • Used in car battery 
    • Used to make fertilizers
    • Used to make dyes and detergent

5. 

  1. Writ chemical equation of the reaction that occurred
    • Zn(s) + CuSO4(aq)  →  ZnSO4(aq) + Cu(s)
  2. Why is it necessary to use excess zinc powder?
    • To ensure that all Culions are displaced
  3. State and explain one observation made by the end of the experiment 
    • Brown solid formed; copper metal is deposited
    • Blue solution turns colourless; Cuare removed from solution
  4. Determine the molar enthalpy change in the reaction that occurred.
    • Mass = 125 x 1 = 125g
      △T = 29-24= -5°C
      △H = MCDT = 125 x 4.2 x 5
                          1000
      = 2.625kJ
      = -2.625kJ
      Moles = 0.75moles = 100cm3
      ? = 125cm3
      125 x 0.75
           1000
      = 0.09375 moles
      0.09375 moles= 2.625kJ
      1mole              =    ?
      -2.6652 x 1
         0.09375 
      = -28.0kJ/mol
  5. State Hess's Law
    • The energy change that occurs in converting reactants to products is the same regardless of the route in which the chemical change occurs.
  6. Using an energy cycle diagram calculate the enthalpy of formation of ethyne from its constituent element 
    q5 jhgfuygy

6. 

  1. Give the half-cell equation for each half cell 
    • A(s) → A2+(aq) + 2e-
    • B2+(aq) + 2e- → B(l)
  2.  Write the overall cell equation 
    • A(s) + B2+(aq) → A2+(aq) + B(s)
  3. Calculate the e.m.f of the cell above
    • E cell = E reduced - E oxidized
      = -0.13-(-0.76) = +0.63V
  4. Describe how salt bridge helps in maintaining the charge balance in each half cell when the cell is in operation
    • It provide the ions to replace those ions that are used up/ formed.
  5. It is not advisable to use potassium chloride salt bridge when lead (II) nitrate solution is used as an electrolyte in the above set-up. Explain
    • Pb2+ will combine with CI to form insoluble PbCI2
  6.                                    
    1. state Faraday's law o electrolysis 
      • The mass of a substance produced during electrolysis is directly proportional to the quantity of electricity passed.
    2. Work out formula of the ions of metal M
      Q = it
      10 x (60 x 60) + 30 x 60
      = 54000C
      9.67g = 54000C
      52g    = ?
      52 x 54000 = 290382.6C
            9.67
      IF = 96500C
       ? = 290382.6C
      = 290382.6 x 1
              96500
      = 3.0
      +3      M3+

7.

  1. graph of counts per minute against time
    q7 uyguysf
    Use graph to determine the half-life of iodine - 128
    • 41 minutes (see graph)
  2. What is the count rate after
    • 12 minutes - 192.5 (see graph)
    • 22 minutes - 165.0 (sce graph)
  3. mass number
    • 128 = 8 +0+a
      a=120
      Atomic number
      53 = 4-1 + b
      b-50
  4. State 2 uses of radioactive isotopes in agriculture
    • Absorption of phosphate fertilizers
    • To follow the path of carbon during plant growth

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