Chemistry Paper 2 Questions and Answers - Asumbi Girls Highschool Pre-Mock Exams May-June 2022

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Instructions to candidates.

  • Write your name and adm number in the spaces provided above.
  • Sign and write the date of examination in the spaces provided above.
  • Answer All the questions in the spaces provided.
  • KNEC mathematical tables and silent non-programmable electronic calculators may be used.
  • All working MUST be clearly shown where necessary.
  • All answers should be written in the spaces provided.
  • This paper consists of 12 printed pages.
  • Candidates should check the question paper to ascertain that all the pages are printed as indicated and that no questions are missing.
  • Candidates should answer all the questions in English.

For Examiner’s Use Only


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    1. The grid below represents part of the periodic table. Study it and answer the questions that follow.
      The letters do not represent the actual symbols of the elements.
      1 yaytada
      1. Which element will require the least amount of energy to remove one of the outermost electrons? (1mk)
      2. Select the most reactive non-metal. (1mk)
      3. Which of the elements has the greatest tendency of forming covalent compounds? Explain (2mks)
      4. What name is given to the family of elements to which elements O, T and B belong?(1mk)
      5. An element W has atomic number 15.m indicate the position of W on the grid. (1mk)
      6. Explain why the atomic radius of S is smaller than that of R. (2mks)
      7. Explain why the atomic radius of Z is smaller than its ionic radius. (1mk)
    2. Study the information given in the table below and answer question that follow.
      1 b auygdytada
      1. Give two chlorides that are liquids at room temperature. Give a reason for your answer. (2mks)
      2. Give a possible reason why AlCl2 has much lower boiling point MgCl2 although both Aluminium and Magnesium are metals. (2mks)
  2. The figure below represents a set up that can be used to prepare sulphur (VI) oxide. Study it and answer the questions that follow.
    2 augdada
    1. Name substance M and N (1mk)
    2. State the function of substance N. (1mk)
    3. Given that the equation for the reaction that occurs is
      2SO2(g) + O2(g) ⇌ 2SO3(g)∆H=-197kJ
      What information about the reaction is provided by ∆H=-197kJ? (1mk)
    4. Give the name of the method of gas collection shown above. (1mk)
        1. What is the advantage of using calcium oxide instead of anhydrous calcium chloride in the experiment above? (1mk)
        2. Concentrated sulphuric (VI) acid is manufactured in large scale through contact process
          1. Identify two substances that are recycled during contact process. (1mk)
          2. Why is recycling necessary? Give two reasons (1mk)
        1. Sulphur (IV) oxide gas is removed by scrubbing in the contact process. What is meant by scrubbing? (1mk)
        2. Write an equation showing how sulphur (IV) oxide is scrubbed. (1mk)
        1. Explain why sulphur (VI) oxide is dissolved in concentrated sulphuric (VI) acid and not in water during contact process. (1mk)
        2. Given that a concentrated solution of suhuric (VI) acid is 18.2M, determine the volume of the concentrated sulphuric (VI) acid that can be mixed with distilled water to make one litre of 2M sulphuric (VI) acid solution. (2mks)
  3. Use the standard electrode potential for the elements A, B, C and D given below to answer the questions that follow. The letters do not represent the actual symbols of the elements.
                                 Eθ (volts)
    A+2(aq) + 2e-  → A(s) -0.76
    B+2(aq) + 2e-  → B(s)  -0.44
    C2(g) + 2e-  → 2C-(aq)  +0.54
    D+4(aq) + e-  → D+3(aq)  +1.61
    1. Which element is the:
      1. Strongest oxidizing agent. (1mk)
      2. Strongest reducing agent (1mk)
      1. Draw a labeled diagram of the electro chemical cell that would be obtained when half cell of element A and B are combined.
      2. Calculate the E^θvalue of the electrochemical cell constructed in 3b (i) above (1mk)
      3. Which two elements if used together in a cell would produce the largest e.m.f. (1mk)
    3. Calculate the number of faradays required to completely reduce 0.1 mole of Fe+3 to Fe (2mks)
    4. One of the major application of electrolysis is electroplating. In chromium plating the steel article is usually plated first with nickel or copper then chromium in a plating both which contain chromium compounds in sulphuric (VI) acid water. Chromium deposits on the article.
      1. Give a reason why steel parts are chromium plated. (1mk)
      2. Why is it necessary for the steel to be mated first with nickel or copper before chromium is applied. (1mk)
      3. Give an ionic equation for the process responsible for chromium plating. (1mk)
      4. If an electrical current of 4.5 amperes is passed through the chromium plating for 20 hours, what would be the mass of steel article? (Cr=52.0, 1 faraday = 96,500 coulombs) (3mks)
        (Oxidation state of chromium = +2)
  4. Study the flow chart below and answer questions that follow.
    4 autgdad
    1. Name substance J and draw its structural formula. (2mks)
      Structural formula
    2. What reagent and conditions are necessary for: (2mks)
      1. Step III
      2. Step II
    3. Name the following
      1. L (1mk)
      2. Gas P (1mk)
      3. Q (1mk)
      4. M (1mk)
    4. Write the equation of the reaction that occur in step P (1mk)
    5. Give the name of process in step V (1mk)
    6. If the relative molecular mass of R is 21,000. Determine the value of n (C=12.0, H =1.0) (2mks)
  5. A student set up the apparatus shown below in order to determine the percentage by volume of oxygen in the air. Study it and answer the questions that follow.
    5 auygdada
      1. State one observation made in the measuring cylinder at the start of the experiment. Explain (2mks)
      2. The pH of the contents of the beaker at the end of the experiment was found to be 4. Explain the observation (2mks)
      3. The volume of air in the measuring cylinder at the end of the experiment was measured study the data given below and answer the questions that follow.
        Volume of air at start of the experiment =36.65cm3
        Volume of air at the end of the experiment =24.28cm3
        Determine the percentage volume of oxygen in the air (1mk)
    2. State and explain the observation made when a mixture of magnesium powder and copper (II) oxide is heated in a crucible. (2mks)
    3. State two air pollutants produced by motor vehicles. (1mk)
    1. The results below were obtained in an experiment conducted by form 3 students from Ratansi secondary school using magnesium.
      Mass of the crucible + Lid =19.52g
      Mass of the crucible + Lid + Magnesium ribbon =20.36g
      Mass of the crucible + Lid + magnesium oxide = 20.92g
      1. Use the results to find the percentage mass of magnesium and oxygen in magnesium oxide. (2mks)
      2. Determine the empirical formula of magnesium oxide. (Mg=24, O= 16.0)
    2. Sodium hydroxide pellet were accidentally mixed with sodium chloride, 8.8g of the mixture were dissolved in water to make one litre of solution. 50cm3 of the solution was neutralized by 20.0cm3 and 0.25M sulphuric (VI) acid
      1. Write an equation for the reaction that took place. (1mk)
      2. Calculate the:
        1. Number of moles of the substance that reacted with sulphuric (VI) acid. (2mks)
        2. Number of moles of the substance that would react with sulphuric (VI) acid in the one litre solution. (1mk)
      3. The percentage of sodium chloride in the mixture. (2mks)
    1. Use the bond energies given in the table below to calculate the enthalpy change for the reaction. (2mks)
      C2H6(g) + Br2(g) → C2H5Br(g) +HBr(g)


      C – H

      C - Br

      Br – Br

      H- Br

      Bond energy KJ/mol





    2. On the space provided below, sketch the cooling curve that would be obtained when a boiling tube Containing water at 80ºC is immersed in a freezing mixture maintained at 10ºC. (2mks)
    3. Butane C4H10 cannot be prepared directly from its elements but its standard heat of formation (∆Hʄθ) can be obtained indirectly.
      The following heats of combustion are given.
      ∆HCθ (Carbon) = -393kJ/mol
      ∆HCθ (Hydrogen) = -286kJ/mol
      ∆HCθ (Butane) =-2877kJ/mol
      1. Draw an energy cycle diagram linking the heat of formation of butane with its heat of combustion and the heat of combustion of its constituents elements. (2mks)
      2. Calculate the heat of formation of butane ∆Hʄθ (C4H10) (2mks)
    4. Given that the lattice enthalpy of potassium chloride is +690kJ/mol and hydration enthalpies of K+ and Cl- are -322kJ and -364kJ respectively. Calculate the enthalpy of solution of potassium chloride. (2mks)


      1. V
      2. S
      3. Q Neither gain nor lose electrons’ hence only give more room for bond formation
      4. Alkali metals
      5. On the grid
      6. It ionizes by receiving an electron , hence the gained electrons repelled by the already existing electrons
      1. SICl4, PCl5, SCl2,
        Melting below room temperature and boiling point above room temperature
      2. AlCl3 has simple molecular structure with weak van der waal forces , while MgCl2 has giant ionic structure with strong ionic bond
      1. M- Vanadium (V) oxide√
        N- Concentrated sulphuric (VI) acid
      2. To dry the gases SO2 and air√1
      3. Forward reaction is exorthermic
        197KJ energy is produced when 2 moles of SO3 are formed
        98.5 KJ are produced when 1 mole of SO3 in addition to keeping the boiling tube dry
      4. Deposition/solidification
      5. CaO reads with the escaping SO3 in addition to keeping the boiling tube dry.
        1. Sulphur (IV) oxide gas √ ½
          Oxygen gas (air) √ ½
        2. reduces environmental pollution √ ½
          Reduces costs √ ½
        1. Is the removal of acidic gases by reacting it with a base e.g SO2 reacted with Ca(OH)2
        2. SO2(g) + Ca(OH)2(s) → CaSO3(s) + H2O(l)
      3. SO3 reacts with water producing a lot of heat which causes acid mists or sprays which are corrosive √1
    3. C1V1=C2V2
      1.82 x V1= 2x1000√1
      V1= 2000 √1
      = 109.8901cm3√1
      1. D+4
      3. A (s)
        b sfsffsfs
      2. emf + E red - E ox
        - .44 ---0.776 = 0.32v
      3. D4+ /D3 and As /A2+
        fe3+( ag ) + 3 e →  fe(s)
        1 mole    3mole    1 mole
        - o.1 mole of fe 3+ + 0.1 * 3= 0.3 feraday
      1. to prevent steel from rusting
      2. to prevent steel from reacting with chromium at higher temperature since copper or nickel are uncreative
      3. Fe24 (ag) + CV (S) - Cv2+ (ag) + F4 (s)
      4. Q = It = 4.5 x 20 x60 x 60 = 324 ,000c
        Mass deposited = 52 x 3240000/ 96500/2 = 87.295 g
    1. propane
      4 adaaaddadad
      1. Reagent – concentrated sulphuric (vi) acid
        Condition: 16º - 180º c
      2. condition:uv light /sunlight
      1. carbon(iv) oxide
      2. hydrogen
      3. propane-I-oic acid
      4. Bromo-propan – 2-01
        2 bromopropane -1 -01
    4. 2 C3H7 ,OH(I) + 902 (g) - 6Co 2 (g) + 8 H2O (g)
    5. Addition polymerization /polymerization
    6. 3x12x 1x 6 = 42
      N = 2100/ 42 = 500
      1. phosphonessmolders
        Itsreaction with air is exothermic
      2. phosphorous (iii)oxide formed is an acidic oxide which dissolves in water to form phosphoric oxide.
        phosphoric(iii) acid
      3. volume of air used = 30.65 – 24. 28 = 637 cm
        percentage volume = 6.37/30.65 * 100 = 20.78%
    2. black powder changes to red brown bead
      brownbeed Mg reduces Cv0 to copper metal
      White ash formed : Mg is oxidized to Mg0
    3. carbon 9ii0 oxide
      Sulphuric (iv) oxide
      Nitrogen (iv) oxide
      1. mass of magnesium = 20.36 – 19.52= 0.849
        Mass of oxygen = 20.92= 20.36=0.56g
        Mass of Mg0 = 20.92 – 19.52 = 1.40g
        % of magnesium = 0.84/ 1.40* 100 =60%
        % of mass of oxygen Mg0= 0.56/1.40*100= 40%
      2. elements present Mg 0
        Mass 0.84 0.56
        molespresent 0.84/24 0.56/16
        0.035 0.035
        Simple ratio
        Formula Mg0
    1. 2 Na0H (ag) + H2 So4 - Na2S04 (ag) = 2 H20
    2. I : moles ratio of Na0H ;H2SO4 = 2:1
      Moles of Na0H = 2 x 0.005 = 0.01
    3. if 50 cm3of Na0H = 0.01
      1000 cm3 of Na0H = 1000 x 0.01/50 8 0.02moles
      OR Ans in (i) x 1000 /50 = Ans
    4. molar mass of Na0H = 23 +1 =16 = 40 G
      Mass of Na0h reacted = 40 x 0.2 = 8g
      Mass of NaCL = 0.8/8.8 x 100 = 9.0909%

    1. 7 adadad
      Bond breaking energy = 413 +193 = 606kj
      Bond function energy = 280 +365 = 645 kj
      H for the reaction = 606- 645
      = 39 kj
      Temp 80
    2. 5 sfsfs
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