CHEMISTRY PAPER 2 - 2019 KCSE STAREHE MOCK EXAMS (QUESTIONS AND ANSWERS)

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INSTRUCTION TO CANDIDATES

  • Answer ALL the questions in the spaces provided in the question paper.
  • KNEC Mathematical tables and silent non-programmable electronic calculators may be used.
  • All working MUST be clearly shown where necessary
  • Candidates should answer all the questions in English.
  1. A few drops of sulphuric acid were added to four test-tubes containing cations as shown below.
    chem1mg
    1.  
      1. In which test-tubes were white precipitate formed?    (1 mark)
      2. Write the chemical formula of the precipitate formed.   (1 mark)
      3. State and explain the observations that would be made in test-tube B when aqueous ammonia is added drop-wise until in excess.  (2 marks)
      4. State and explain the observation that would be made when little amount of sodium stearate solution are added in test-tube D.  (2 marks)
    2. Study the flow chart below and answer the questions that follow.
      chem1bmg
      1. What is the type of detergent prepared in this process?    (1 mark)
      2. Explain the cleaning of action of the detergent.     (2 marks)
    3. Using an ion equation show how sodium carbonate removes water hardness. (1 mark)
  1. The table below gives formulae and volumes occupied by 1 g of some gases at s.t.p. Study it carefully to answer the questions that follow.

    Formula of gas

    Ne

    C2H2

    O2

    Ar

    NO2

    SO2

    SO3

    Relative Molecular Mass

    20

    26

    32

    40

    46

    64

    80

    Volume (cm3)

    1120

    862

    700

    560

    487

    350

    280


    1. Plot a graph of volume of gas (y-axis) against the relative molecular mass.    (3 marks)
    2. Use the graph to predict the volume occupied at s.t.p by
      1. 1g of hydrogen chloride gas (Cl=35.5, H=1) (1 mark)
      2. 1g of carbon (II) oxide. (C=12, O=16)      (1 mark)
      3. Relative molecular mass of a gas which occupies 508 cm3 per gram at s.t.p. (1 mark)
    3.  
      1. State the Graham’s law of diffusion.   (1 mark)
      2. A gas X diffuses through a porous plug in 60 seconds. Gas Y which is a quarter the volume of gas X diffuses through the same plug in 22.5 seconds. Calculate the relative molecular mass of gas Y. (Relative Molecular Mass of X = 34)                 (3 marks)
    4. A gas occupies 100 cm3 at 0 0C and 1 atmosphere pressure.  Calculate the temperature at which the volume is double and the pressure is halved. (2 marks)
  1. The set up below was used to prepare hydrogen chloride gas and salt T.
    chem3mg
    1. Identify the following
      1. Liquid M (1 mark)
      2. Gas V (1 mark)
      3. Salt T  (1 mark)
    2. Write balanced chemical equations for reactions that occur at:
      1. Flask I  (1 mark)
      2. Combustion tube.  (1 mark)
    3. Name the process that formed salt T as shown in the diagram.                       (1 mark)
    4. Sulphuric (VI) acid is used as a drying agent in this experiment.  Explain why calcium oxide is unsuitable for the same purpose in this reaction.  (1 mark)
    5. The water in the beaker was found to have a pH of 2.0 at the end of the experiment.Explain.  (1 mark)
    6. Calculate the mass of salt T formed if 480 cm3 of hydrogen chloride gas measured at r.t.p was reacted with aluminium powder. (Al = 27, Cl = 35.5, MGV = 24 dm3) (2 marks)
    7. In the space provided below, draw a well labelled diagram showing how you would dissolve hydrogen chloride gas in water.   (1 mark)
    8. Explain why hydrogen chloride gas dissolved in methylbenzene does not react with calcium carbonate.   (1 mark)
    9. Using equation, state the observation made when a gas jar containing hydrogen chloride gas is opened near an open bottle of liquid ammonia.  (1 mark)
  1.  
    1. The grid given represents part of the periodic table. Study it and answer the questions that follow. (The letters do not represent the actual symbol of the elements)
      chem4mg
      1. What name is given to the group of elements to which C and F belong?          (1 mark)
      2. Which letter represents the element that is least reactive?                                (1 mark)
      3. What type of bond is formed when B and E react? Explain.                          (2 marks)
      4. Write the formula of the compound formed when element D and oxygen gas react.      (1 mark)
      5. On the grid, indicate with a tick (√) the position of element G which is in the third period of the periodic table and forms G3- ions.    (1 mark)
      6. Compare the atomic sizes of elements C and D.  Explain.                              (2 marks)
    2. Study the information in the table below and answer the questions that follow.

      Substance

      Melting point
      (oC)

      Boiling point (oC)

      Solubilty in water

      Density at room temperature g/cm3

      H

      -117

      78.5

      Very soluble

      0.8

      J

      -78

      -33

      Very soluble

      0.77 × 10-3

      K

      -23

      77

      Insoluble

      1.6

      L

      -219

      -183

      Slightly soluble

      1.33 × 10-3


      (The letters do not represent the actual symbols of the substances).
      1. Which substance is a liquid at room temperature and when mixed with water two layers would be formed?  (1 mark)
      2. Determine the melting point of H in Kelvin?                                                        (1 mark)
      3. Which letter represents a substance that is a gas at room temperature and which can be Collected by downward displacement of air? (Density of air is 1.29 × 10-3 g/cm3 at room temperature). Explain.   (2 marks)
  1.  
    1. The table below gives standard electrode potentials for the metals represented by the letters A, B, C and D.  Study it and answer the questions that follow.

                  Metal

      Standard electrode potential, E0(Volts)

      A

      B

      C

      D

      -0.13

      +0.85

      +0.34

      -0.76


      1. Arrange the metals in a decreasing order of reactivity.                                 (1 mark)  
        Metals C and D were connected to form a cell as shown in the diagram below.
        chem5mg
      2. Write the equations for the reactions that occur at electrodes.                   
        C   (1 mark)
        D  (1 mark)
      3. On the diagram, indicate with an arrow the direction in which electrons would flow.(1 mark)
      4. What is the function of the part labelled X.                                                (1 mark)
      5. Calculate the e.m.f of the cell formed in the diagram.                                 (1 mark)
    2. An electric current was passed through a concentrated solution of copper (II) chloride as shown in the diagram below.
      chem55bmg
      1. Write the chemical equation of reaction at cathode?   (1 mark)
      2. After sometime test-tube Z was found to contain a mixture of two gases. Explain this observation. (2 marks)
      3. State the observations that would be made at the anode if the platinum electrodes are replaced with copper electrodes.  (2 marks)
  1. The list below shows the formula of some organic compounds. Use it to answer the questions that follow. Use the letters T1 to T6.
     T1 – CH3CH2CH2CH3
     T2 – CH3CH2CH2COOC2H5
     T3 – CH3CH2CH2CH2OH
     T4 – CH3CH2CH2COOH
     T5 – CH3CH2CHCH2
     T6 – CH3CCCH3
    1. Select a compound which.
      1. Will produce bubbles of a gas when reacted with sodium carbonate.         (1 mark)
      2. Will decolourise both bromine water and acidified potassium permanganate. (1 mark)
      3. Will produce hydrogen gas when reacted with sodium metal.                  (1 mark)
      4. Represents a saturated hydrocarbon.     (1 mark)
      5. Is likely to undergo polymerization.    (1 mark)
    2. Using two molecules show how polymerization in T5 occurs.   (1 mark)
    3. Name the process by which compound T2 is formed and identify the compounds that were used to form it.
      Process                  (1 mark)
      Compounds           (1 mark)
    4. Compound T3 can be converted to T4 as shown by the equation below.
      C3H9OH + O2 → C3H7COOH + H2O
      Given the following information
      ∆Hc       C3H9OH = -4910 kJmol-1
      ∆Hc       C3H7COOH = -4090 kJmol-1
      Determine the heat change for the reaction above.    (3 marks)
  1. The set-up below can be used to generate a gas.
    chem7mg
    1.  
      1. Complete the table below giving the names of substance K and L if the gases generated are carbon (IV) oxide and carbon (II) oxide.  (2marks)

        Substance

        Carbon (IV) oxide

        Carbon (II) oxide

        K

           

        L

           
      2. Complete the diagram to show how a sample of carbon (II) oxide can be collected.(2marks)
      3. State two ways that can be used to distinguish carbon (IV) oxide from carbon (II) oxide?  (2 marks)
    2.  
      1. In an experiment, carbon (IV) oxide gas  was passed over heated charcoal held in a combustion tube. Write a chemical equation for the reaction that took place in the combustion tube.   (1 mark)
      2. State one use of carbon (II) oxide.    (1 mark)
    3. The following set ups were used by Form Two students. Study and use them to answer the questions that follow.
      chem7cmg
      State and explain the difference in observation made in set up I and II above.       (3 marks)

MARKING SCHEME

  1.  
    1.  
      1. A and C
      2. BaSO4 and PbSO4
      3. White precipitate soluble in excess aqueous ammonia. When a few drops of aqueous ammonia are added insoluble zinc hydroxide / Zn(OH)2(s) is formed √½ which dissolves in excess aqueous ammonia to form soluble complex of tetraamine zinc (II) ion / [Zn(NH3)4]2+(aq). √½
      4. White precipitate is formed (scum) due to formation of insoluble magnesium stearate / Mg(C17H35COO)2(s).
    2.  
      1. Soapless detergent √
      2. The non-polar end of detergent molecule dissolves in the grease while the polar end dissolves in water √. This loosens grease to form micelle which are carried away by rinsing water.√
    3. Mg2+(aq) + CO32-(aq) → MgCO3(s) or Ca2+(aq) + CO32-(aq) → CaCO3(s)
  1.  
    1.  
      chem2youmg
    2.  
      1. 620 cm3 √ (working must be shown on the graph)
      2. 790 cm3
      3. 44 √
    3. The rate of diffusion of a gas is inversely proportional to the square root of its density under the same conditions of temperature and pressure. √
    4. RX = 1/60 = 0.0167 √½
      RY = 0.25/22.5 = 0.0111 √½
      0.0167/0.0111 = square root (Y/34) √
      (0.0167/0.0111)2 = Y/34
      Y = (0.0167/0.0111)2 × 34 = 76.96 √               
    5. P1V1 = P2V2
       T1           T2
      1 × 100 = 0.5 × 200
        273             T2
      T2 = 273 K √
  1.  
    1.  
      1. Conc. Sulphuric (VI) acid /sulphuric acid √      Acc. formula
      2. Hydrogen gas // H2
      3. Aluminium Chloride // AlCl3 √                                                       
    2.  
      1. NaCl(s) + H2SO4(l) → Na2SO4(aq) + 2HCl(g) √ or Deny ½ if state symbols wrong or missing
        H2SO4(l) +   Cl-(aq) → H2SO4(aq) + HCl(g)
      2. 2Al(s) + 6HCl(g) → 2AlCl3(s) + 3H2(g)  
    3. Sublimation √
    4. Gas is acidic, therefore reacts with the basic calcium oxide √            
    5. Unreacted HCl gas √ dissolves forming a strong acidic solution √ Acceppt correct equation                          
    6. Moles of HCl       = 480     =   0.02 moles √½
                                24000
      Moles ratio HCl:AlCl3 = 3:1
      Moles of AlCl3 = 0.02 × 1/3 = 0.0066 moles √½                                                         
      RFM = 133.5P½
      Mass of T = 0.0066 × 133.5 = 0.8811 g √½
    7.  
      chem3gyoumg
      Diagram = √½, Labelling = √½
    8. In methyl / benzene HCl exists in molecular form and there are no H+ ions to react with the carbonate √½ 
      HCl(g ) + NH3(g) → NH4Cl (s)   √ ½                                            
      White Fumes √ ½ The observation must be mentioned / indicated
  1.  
    1.  
      1. Alkaline earth metals √
      2. A√
      3. Covalent √. They form bond by sharing of electrons since they are both non-metals √
      4. D2O3
      5. Group V and period 3 √
      6. D has small atomic radius than C √, due to increased nuclear charge across the period which pull electrons closer to the nucleus. √
    2.  
      1. K √
      2. -117 + 273 = 156K √
      3. J √ because its BP is higher than room temperature and is less denser than air √
  1.  
    1.  
      1. D > A > C > B √
      2. C2+(aq) + 2e - → C(s)
        D+(aq) → D(s) + 2e-
      3.  
        chem5youmg
      4. To complete the circuit / balance the charges
      5. e.m.f = +0.34 – (-0.76) √
        = + 1.10 volts √
    2.  
      1. Cu2+(aq) + 2e- → Cu(s)
      2. Initially the Cl- ions are at higher concentration hence preferentially discharged to form chlorine gas √ but with time the concentration of Cl- goes down hence OH- ions are discharged to produce of oxygen gas. √                                             
      3. No gas will be evolved; √ Anode dissolves. √
  1.  
    1.  
      1. T4
      2. T5 / T6 for any one √
      3. T3 / T4 for any one √
      4. T1
      5. T5 / T6 for any one √
    2.  
      chem6byoumg              
    3. Process – Esterification
    4. Compounds - chem6cyoumg
    5. C3H9OH + O2 → C3H7COOH + H2O    ∆H1 =?
      C3H7COOH + 5O2 → 4CO2 + 4H2O     ∆H2 = -4090 kJmol-1
      C4H9OH + 6O2 → 4CO2 + 5H2O         ∆H3 = -4910 kJmol-1
      ⸫ ∆H1 = ∆H3 - ∆H2 = -4910 –(-4090) = -820 kJmol-1
      OR
      chem6dyoumg
  1.  
    1.  
      1.  

        Substance

        Carbon (IV) oxide

        Carbon (II) oxide

        K

        Dilute hydrochloric acid √½

        Concentrated sulphuric (VI) acid √½

        L

        Marble chips or calcium carbonate √½

        Sodium methanoate or ethanedioc acid (oxalic acid) √½

      2.  
        chem27mg 
        Complete diagram = 1 mark, Labelling = 1 mark
      3. Carbon (IV) oxide reacts with lime water / calcium hydroxide solution to yield white precipitate while carbon (II) oxide does not. √ Carbon (II) oxide burns with blue flame while carbon (IV) oxide does not burn. √
    2.  
      1. CO2(g) + C(s) → 2CO(g)
      2. Reducing agent in extraction of some metals from their oxides. √
    3. The bulb lights in set up I or conducts electricity while set up II does not. √ In graphite, three out of four valence electrons of carbon atom are bonded leaving one delocalised electron thus conducts electricity √ while in diamond, all the four valence electrons are bonded and is without delocalised electrons. √
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