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

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 - 110^oC)
   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.                 
   

   A		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
   c		Effervesence or observed bubbles of a gas evolves	Presence of R- COOH ions or H+