Chemistry Paper 3 Questions and Answers with Confidentials - Form 4 End Term 1 Exams 2022

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Questions 

  1.      
    1.      
      • You are provided with solutions M and N.
      • Solution M is acidified potassium manganite VII containing 3.16g/litre of solute.
      • Solution N was prepared by dissolving 4.17g of solid N.
      • FeSO4.XH2O is distilled water to make 250cm3 of solution.

        You are required to determine the value of X in formula FeSO4.XH2O

        Procedure
      • Place solution M in a burette. Pipette 25cm3 of solution N into a 250cm3 conical flask.
      • Titrate solution N with solution M until a permanent pink colour just appears. Record your results in the table below.
      • Repeat the above procedure two more times.
          I II III
        Final burette reading               
        Initial burette reading      
        Volume of solution M
        below(cm3)
             
        (4 mks)
    2. Calculate the average volume of solution M used. (1 mk)
    3. Determine the:
      1. Concentration of potassium manganite VII in moles per litre.
        (K = 39, Mn = 55, O = `16) (2 mks)
      2. The number of moles of potassium (VII) used. (2 mks)
    4. Calculate the concentration of solution N in grams per litre. (2 mks)
    5. Given the ionic equation for the above equation reaction is:
      MnO-4(aq) + 5Fe2+(aq) + 8H+(aq)→ Mn2+(aq) + 5Fe3+(aq) + 4H2O(l)
      Determine the number of moles of FeSO4.XH2O in:
      1. 25cm3 of solution N. (1 mk)
      2. 100cm3 of solution N. (1 mk)
    6. Using the values, calculate in (d) and (e) (ii) above, determine:
      1. The Relative formula mass of FeSO4.XH2O (2 mks)
      2. The value of X in the formula FeSO4.XH2O given (Fe = 56, S = 32, O = 16, H = 1) (2 mks)
  2. You are provided with:
    • About 1.5gd of metal P – Magnesium powder
    • About 1.6g of metal Q – Zinc powder
    • Exactly 0.5M FeSO4, solution
    • Exactly 0.5 CUSO4, solution T

      You are required to determine the molar enthalpy of displacement of Copper II ions using metal P.

    • Procedure I
    • Place exactly 25cm3 of solution in 100ml plastic beaker. Measure the initial temperature of the solution and record it in table II below. Add all of the metal P at once. Stir the mixture carefully with the thermometer. Record the highest temperature reading in the table below. (1 mk)
      1.        
        Final temeprature °C                      
        Initial temeprature °C                          
      2. Determine the change in temperature, ∆T1. (1 mk)
      3. Calculate the:
        1. Heat change for the above reaction.(Assume the specific heat capacity of the solution is 4.2j/g/k, and density of solution is 1g/cm3) (2 mks)
        2. The molar enthalpy of displacement of Fe2+ with P; ∆H1. (1 mk)
      4. Write thermochemical equation for this reaction. (1 mk)

    • Procedure II
    • Place exactly 25cm3 of solution T in 100mly plastic beaker. Measure the initial temperature of the solution and record it in the table III below. Add all of the metal Q at one. Stir the mixture carefully with the thermometer and record the highest temperature reached in the table III below.
      1.   
        Final temeprature °C                      
        Initial temeprature °C                          
      2. Determine the change in temperature, ∆T2. (1 mk)
      3. Calculate the:
        1. Heat change for the above reaction.
          (Assume the specific heat capacity of solution is 4.2j/g/k, density is (g/cm3)(1 mk)
        2. Molar heat of displacement of Cu2+ with metal Q (∆H2) (2 mks)
      4. Write the thermochemical equation for this reaction. (1 mk)
      5. Using the two thermochemical equations above, determine the heat change for the determine the heat change for the reaction. (2 mks)
        Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s) ∆H =
  3.          
    1. You are provided with solution U, carry out tests below. Write your observations and inferences in the spaces provided.
      Divided the solution into five portions.
      1. To the first portion add aqueous Sodium hydroxide dropwise until in excess.
        Observations Inferences
           
      2. To the 3rd portion add aqueous ammonium hydroxide dropwise until in excess.
        Observations Inferences
           
      3. To the 3rd portion add 2.3 drops of 1M HCl
        Observations Inferences
           
      4. To the 4th portion, add 2 – 3 drops of Barium Nitrate.
        Observations Inferences
           
      5. To the 5th portion, add 2 – 3 drops of Lead II Nitrate solution then warm the mixture.
        Observations Inferences
           
    2. You are provided with solid S. Carry out the tests below. Record your observations and inferences in the tables below.
      Place all solid S into a boiling tube. Add about 5cm3 of distilled water and shake well.
      Divide it into three portions.
      1. To the first portion, add 2 – 3 drops of bromine water.
        Observations Inferences
           
      2. To the second portion, add 2 – 3 drops of acidified potassium dichromate VI solution and shake well.
        Observations Inferences
           
      3. To the third portion, add a small amount of solid Sodium hydrogen carbonate. 
        Observations Inferences
           

Confidential

In addition to the apparatus and fittings found in a Chemistry Laboratory, each candidate will require the following:

  1. About 75cm3 of solution M
  2. About 100cm3 of solution N
    3. A burette
    4. A pipette
    5. Two conical flasks
    6. About 1.5g of metal P
    7. About 1.6g of metal Q
    8. About 40cm3 of solution S
    9. About 40cm3 of solution
    10. A thermometer (0 - 110oC)
    11. 2 plastic beakers 100ml
    12. A measuring cylinder 50ml
    13. About 10cm3 of solution U
    14. About 0.5g of solid J

ACCESS TO:

  1. 2M Sodium hydroxide
  2. 2M Ammonium hydroxide
  3. 1M Lead II Nitrate Supplied with a dropper
  4. 0.5M Barium Nitrate
  5. 0.5M Hydrochloric acid

NOTES:

  1. Solution M is prepared by dissolving 3.2g of KMnO4 in 400cm3 of Sulphuric acid and diluting to one litre of solution using distilled water.
  2. Solution N is prepared by dissolving 16.7g of FeSO4.7H2O in 400cm3 of 1MH2SO4 and diluting to one litre of solution using distilled water. The solid should be dissolved in the Sulphuric acid immediately after weighing.
  3. Metal T is magnesium powder.
  4. Metal Q is Iron powder
  5. Solution S is 0.5M FeSO4
  6. Solution U is 0.5M AlCl3
  7. Solid J is maleic acid

Marking Scheme

Table 1

Depending on the school value:

  1.         
    1.         
    2.       
    3.          
      1. Conc of KMnO4 in moles per litre
        K= 39, Mn= 55, O=16
        3.16/158 = 0.02 moles per litre
      2. Number of moles of KMnO4 use
        = molarity x volume
                1000
        = 0.02 x 15
             1000
        = 0.0003 moles

    4.     Conc of solution N in g/litre
      4.17 g → 250cm3
      ?    → 1000cm3
      1000 x 4.17
         250
      = 16.68 g/litre
    5.          
      1. Ratio of MnO-: Fe2+= 1:5
      2. Number ofmoles od 25cm3 of N
        = 5 x 0.003 = 0.0015 moles

      3. Number of moles of present in 1000m3 of N
        if 0.0015 moles are in 25cm3
             ?    in 1000cm3
        1000 x 0.0015
             25
        = 0.06M
  2.         
    1. Table II
      Final temp (x) 48        41     
      Initial temp (x) 24        24

    2. ΔT1 = 48-24 = 24°
      ΔT2 = 41 -24 = 17°


    3.        
      1. ΔH1 = 25g x 4.2j/gk = 2520j or 2.52KJ

        ΔH2 = 25g x 4.2j/g x K x 17K = 1785KJ or 1.785 KJ


      2. Moles reacted
        = 2.5 x 0.5 = 0.0125 moles
            1000
        0.0125 moles = 2.52 KJ
        1 mole →  ?
        = 1 mole x 2.52 KJ = 201.6 KJ/mol
            0.0125 moles

        1 mole x 1.785  = 142.8KJ/mol
            0.0125

    4. Mg(g) + Fe2+(aq) → Mg2+(g) + Fe(s) ΔH = -201.6KJ/mol

      Fe(s) + Cu2+(aq) → Fe2+(aq) + Cu(s) ΔH= -142.8 KJ/mol

    5. Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s) ΔH = -344.4KJ/mol
  3.                 
    Observation Inferences
     a A white precipitate observed and dissolved in excess Al3+. Zn2+, Pb2+ present
    b White precipitate observed and insoluble in excess Al3+, Pb2+ present or Zn2+ absent
    c No white precipitate observed  Al3+ present
     d No white precipitate observed SO32- , SO42-, CO32- ions absent
     e White precipitate observed but dissolves on warning Cl- ions confirmed present
     
    B Observation Inferences
    a Dissolves to form a colourless solution Soluble salts
    Polar substance
    b Bromine water decolourised Unsaturated hydrocarbons present
    or 
         ChemForm4ET122p3qa3b 
                        
    c Effervesence or observed bubbles of a gas evolves Presence of R- COOH ions or H+

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