CHEMISTRY PAPER 2 - FORM 4 END TERM 1 EXAMS 2020

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INSTRUCTIONS TO CANDIDATES

  • Write your name and admission number in the spaces provided.
  • Sign and write the date of examination in the spaces provided
  • Answer all the questions in the spaces provided
  • All working must be shown where necessary
  • Electronic calculators and mathematical tables may be use.
  1. Study the information given below and answer the questions that follow.

    Element

    Atomic radius(nm)

    Ionic radius nm

    Formula of oxide

    Melting point(0c)

    A

    0.364

    0.421

    A2O

    -119

    D

    0.830

    0.711

    DO2

    837

    E

    0.592

    0.485

    E2O3

    1466

    G

    0.381

    0.446

    G2O3

    242

    J

    0.762

    0.676

    JO

    1054


    1. Which elements are non-metals. Give a reason? (2mks)
    2.  
      1. Write a formula of a compound formed when J combines with A(1mk)
      2. What type of bond exist between J and D.(1mk)
    3. Explain why the melting point of the oxide of E is higher than that of the oxide of G.(2mks)
    4.  
      1. Which two elements would react with each other most vigorously. Give a reason. (2mks)
      2. Which element would be suitable for making utensils for boiling water. State two properties that make the elements suitable for the use. (2mks)
    5. Elements Q and R have electronic configuration 2.8.2 and 2.8.6. respectfully.
      1. Explain why the ionic radius of R is expected to be greater than its atomic radius. (1mk)
      2. Write the equation for the reaction between Q and R.(1mk)
  2. The chromatogram below is of and acid enzyme x and y and three simple sugar P, Q and R.
    chemp2chromatogram
    1.  
      1. Name two simple sugars present in both x and y.(2mks)
      2. Name lines L and M.     (2mks)
      3. What property is exhibited by simple sugar x.(1mk)
    2. Two pieces of paper were lowered into different Bunsen burner flames and removed quickly. The results were as shown below.
      charred paper
      Which paper was lowered into a Bunsen burner whose air hole were closed. Explain(2mks)
    3. Oxygen can be obtained industrially by fractional distillation of liquid air
      1. Why is the gas mixture passed through sodium hydroxide solution? (1mk)
      2. In the final stage, which gas is distilled out first? Explain. (1mk)
      3. Name two commercial uses of oxygen gas. (1mk)
  3. Study the flow diagram and answer the questions below.
    flowchart chemp2q3
    1. Identify
      1. White ppt I (1mk)
      2. Solution II (1mk)
      3. Residue U (1mk)
    2. Write ionic equation for the reactions colourless solution (II) with Pb(NO3) 1mk
    3. Write observations that would be made when ammonia solution is added drop wise till in excess to the colourless solution(II) 2mks
    4. Below are PH values of some solutions

      Solution

      Z

      Y

      X

      W

      PH

      6.5

      3.5

      2.2

      7.2

      1. Which solution is likely to be
        1. Acidic rain. (1mk)
        2. Potassium hydroxide (1mk)
      2. A basic substance V reacted with both solutions Y and X. What is the nature of V? (2mks)
      3. Name two substances that shows the characteristics in question (ii) above. (2mks)
  4. Study the flow chart below and answer the questions that follow.
    chemp2flowchartq4
    1. Identify substances A, B, F and G (4mks)
    2. Write down the equation for the formation of
      1. Substance C
      2. E and F
      3. Gas G
    3. Substance D was formed to have molecular mass of 42,000. Determine the number of molecules present in the substances (H=1, C=12) 2mks
    4. State
      1. The condition necessary for the conversion of ethanol to substance A.(1mk)
      2. The catalyst required in the conversion of A and B.(1mk)
  5.  
    1. The table below gives the solubility of hydrated copper(ii) sulphate in mol dm-3 at different temperatures.

      Temperature(0C)

      Solubility mol dm-3

      20

      8 x 10-2

      40

      12 x 10-2

      60

      16 x 10-2

      80

      22 x 10-2

      100

      30 x 10-2

      1. On the grid provided plot a graph of solubility of copper(II) sulphate (vertical axis) against temperature. (3mks
      2. From the graph, determine the mass of copper(II) sulphate deposited when the solution is cooled from 700c to 400. (Molar mass of hydrated copper(ii) sulphate = 250g)
    2. In an experiment to determine the solubility of sodium chloride ,5.0 cm3 of a saturated solution of sodium chloride weighing 5.35g were placed in a volumetric flask and diluted to a total volume of 250cm3. 25.0 cm3 of the dilute solution of sodium chloride completely reacted with 24.1 cm3 of 0.1 M silver nitrate solution.
      AgNO3(aq) + NaCl(aq)   →  AgCl(s) + NaNO3(aq)
      Calculate;
      1. Moles of silver nitrate in 24.1cm3 of solution. (1mk)
      2. Moles of sodium chloride in 25.0cm3 of solution. (1mk)
      3. Moles of sodium chloride in 250cm3 of solution(1mk)
      4. Mass of sodium chloride in 5.0cm3 of saturated chloride solution (Na=23.0 Cu=35.5) (1mk)
      5. Mass of water in 5.0 cm3 of saturated solution of sodium chloride(1mk)
      6. The solubility of sodium chloride in g/100 g of water. (2mks)
  6. The flow chart below shows some of the processes involved in large scale production of sulphur(VI) acid. Use it to answer the questions that follow.
    contact process
    1. Name the process
    2.  
      1. Name substance A. (1mk)
      2. Write an equation for the process that takes place in the absorption tower. (1mk)
    3. Vanadium (V) oxide is commonly used catalyst in the process.
      1. Name another catalyst which can be used for this process. (1mk)
      2. Give two why reasons vanadium (V) oxide is commonly used catalyst. (2mks)
    4. Sate and explain the observations made when concentrated sulphuric (VI) acid is added to crystals copper(ii) sulphate in a beaker(2mks)
    5. The reaction of concentrated sulphuric (VI) acid with sodium chloride produces hydrogen chloride gas. State the property of concentrated sulphuric (VI) acid illustrated in the reaction. (1mk)
    6. Name two uses of sulphuric (VI) acid.2mks
  7. The diagram below shows a set up that can be used for industrial manufacture of hydrochloric acid. Study it and answer the questions that follow.
    chemp2q7term1
    1. Name
      1. Produce F
      2. Substance E
    2. Explain the applications of hydrochloric acid in textile industry. (1mk)
    3. Hydrochloric acid was added to iron powder in a test tube and shaken thoroughly to mix to 1cm3 of the resulting solution, six drops of aqueous solution of ammonia were added.
      1. State the observation made on adding ammonia solution. (1 mk
      2. Explain the observation sated above and write an ionic equation for the reaction. (2mks)
      3. Concentrated hydrochloric is 35% pure with density 1.18g/cm3.Calculate it’s concentration in moles per litre. (3mks)

MARKING SCHEME

  1.  
    1. A 1/2mk and G1/2 mk   1mk
      The ionic radius is larger 1 mk than the atomic radius implying they gain electrons.        
    2. JA2         1mk
      Metallic(1mk
    3. The oxide of E is ionic1mk with a giant ionic structure that requires a lot of energy to break the oxide of G is molecular.(2mks)
    4.  
      1. A and D   1mk
        A is a non-metal with the smallest ½mk atomic radius hence most electronegative
        D is a metal with the smallest atomic radius hence most electropositive. ½mk  
      2. E . 1mk Has high melting point ½mk and good ½mk conductor of heat being a metal .
    5.  
      1. R gains 2es and hence there is less nuclear 1mk charge /attraction than its atom/gains 2es nuclear attracts 20es against 16 electrons in the atom.
      2. Q(s) + R(s )    →    QR(s)        1mk
  2.  
    1.  
      1. P and Q (2mks)
      2. L-Baseline   (1mk)
        M- Solvent front   (1mk)
      3. Most sticky/less soluble(1mk)
    2.  B(1mk)
      Flame B burns completely because its very hot but A has unburnt region hence it contains unburnt region.91mk)
    3.  
      1. Sodium hydroxide solution absorbs carbon (IV) oxide gas(1mk)
      2. Nitrogen gas. Because it has the lowest boiling points.(2mks)
      3. Used in oxyacetylene flame.
        Burning fuels for propelling rockets.
        To remove iron impunities during steel making.   Any 2 – 1mk
  3.  
    1.  
      1. Zn (OH) 2(g)   (1mk)
      2. Zn CL2(aq) (1mk)
      3.  ZnO(s)                                                         (1mk               
    2.  2Cl- (aq) + Pb2+(aq) (1mk)
    3. White ppt formed   (1mk)
      Dissolve in excess       (1mk)
    4.  
      1. I         Z                                           (1mk)
        II       Y                                                               (1mk)
      2. Amphoteric   (1mk)
      3.  Zn (OH)2(s) / zinc hydroxide.                     (1mk)
  4.  
    1. A-Ethane   C2 H4 CH2 =CH2
      B- Ethane C 2 H6 CH3 CH3
      F – Carbon (IV) oxide   CO2
      G- Hydrogen H2                                                                               (4mks)
    2.  
      1. C 2H(g) + Br2(l)      C2H4Bror CH2Br-CH2Br   (1mk)
      2. 2C2H6(g) + 7O2(s)  →  4CO2(g) + 6H2O (g)
        If not balanced = 0mk
        Wrong or missing symbols = 1/2mk
      3. 2Na(s)   + 2H2 O(l)   →   2NaOH9aq) + H2(g)   (2mks)
        Balanced = 2mks
        Not balanced =0mk.
    3. Mass of monomer = 2(12 + 2)= 28
      No.of molecules = 42000    = 15000 molecules                  (2mks)
                                    28
    4.  
      1. Temperature of 1800 c (1mk)
      2. Nickel catalyst (1mk)
  5.  
    1.  
      1. - scale(I)
        -Plotting all points correctly (I)
        - Curve (shape)
      2. 0.188- 0.12 = 0.068 mol(I)
        Therefore mass of hydrated copper(II) sulphate
        = 0.68 x 250 = 17g
    2.  
      1. Moles of AgNO3 = 0.1 x 24.1 = 2.41 10-3
                                       1000
      2. Moles of NaCI = Moles of AgNO3
        = 241 x 10 -3        
      3. Moles of NaCL in 250cm3 = 2.41 x 10-3 x 250
                                                                     25
        =2.41 x 10-2
      4. R.F.M Na CI = 23 + 35 .5 = 58.5
        Mass of NaCl in 5cm3 = 2.41 x 10-2 x 58.5
        = 1.41g
      5. Mass of water = 5.35 – 1.41
        = 3.94g
      6. 3.94 of water contains 1.41g of NaCl
        100 g of water = 1.41 x 100
                                     3.94
        =35.7
  6.  
    1. Contact process=1mk
    2.  
      1. Sulphuric(IV) acid.(1mk)
      2. H2SO 4(aq) + SO3(g)  →   H2S2O7(l)
    3.  
      1. Platinized asbestos            (1mk)
      2. -It is not highly poisoned(2mks)
        -It is cheap
    4. Crystals turn blue to white .Concentrated sulphuric(IV) acid removes water of crystals from hydrated copper(II) sulphate.(2mks)
    5. Concentrated sulphuric (VI) acid is less volatile hence displaces more volatile acids from their salts.(1mk)
    6. Used in;- accumulators.
      - in manufacture of fertilizers.
      - in etching of metals.
      - in manufacture of detergents.(any 2mks)
  7.  
    1.  
      1. Hydrogen chloride gas (HCL (g) 1mk
      2. Water (H2O (l)  1mk
    2. ……………………………..
    3.  
      1. Green ppt(1mk
      2. Insoluble iron (II) hydroxide was formed(1mk)
        Fe2+(aq)   + 2OH (aq)   →  Fe(OH)2(s)   1mk
    4. Mass of 1000cm3 of solution = 1000 x 1.18   1/2mk
      = 1180g 1/2mk
      Mass of HCl = 35  x 1180     ½ mk
                           100
      = 413g   ½   mk
      Molarity          =   413                   ½  mk
                                 36.5
      = 11.3151 M ½mk

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