Chemistry Paper 3 Questions and Answers with Confidential - Form 3 End Term 2 Exams 2023

You are provided with the following:

• 3.3g metal carbonate, MCO₃ , labeled solution Q
• 2M hydrochloric acid, labeled solution P
• Sodium hydroxide, labeled solution R containing 40g/L of solution

You are required to determine the relative atomic mass of metal M

Procedure

1. Measure accurately 100cm³ of solution P into clean 250cm³ conical flak and add all the 3.3g of solid Q, MCO³
2. Shake the mixture well and wait for effervescence to stop. Label the resulting solution as S
3. Pipette 25cm 3 of solution R into a conical flask and add 2-3 drops of phenolphthalein indicator.
4. Fill the burette with solution S and titrate against the solution R until the end point.
5. Record your results in the table below. Repeat the procedure at least two times to complete the table.
    (4 mks)
   

   	i	ii	iii
   Final burette reading (cm3)
   Initial burette reading (cm3)
   Volume of solution S used (cm3)

   
   
   1. What is the average volume of solution S used? (1mk)
   2. Calculate the moles of sodium hydroxide, solution R used. (2mks)
   3. Calculate the moles of hydrochloric acid in the average volume of solution S used. (2mks)
   4. Calculate the moles of hydrochloric acid in 100cm3 of solution S. (2mks)
   5. Calculate the moles of hydrochloric acid in the 100cm3 of the original solution P. (2mks)
   6. Calculate the moles of hydrochloric acid, solution P that reacted with solid Q, MCO₃. (2mks)
   7. Calculate the moles of MCO₃ that reacted. (2mks)
   8. Calculate the relative formula mass (RFM) of MCO₃. (2mks)
   9. Calculate the relative atomic mass (RAM) of metal M. (1mk)

CONFIDENTIAL

Question one

In addition, to the common laboratory apparatus and fittings, each candidate should be provided with:

• About 80cm 3 of solution R
• About 100cm 3 of solution Q
• 1.06g of solid A accurately weighed
• 25ml pipette
•  50ml burette
• 250ml volumetric flask
• 100ml plastic beaker
• Three conical flasks
• Labels
• 50ml measuring cylinder
• Metallic spatula
• source of heat
• boiling tube
• six dry test tube
• Access to methyl orange
  Solid A is anhydrous sodium carbonate

Question two

Solid J (2g) (each student) – prepared by mixing zinc sulphate and ammonium sulphate in the ratio 1:1

• 2 M sodium hydroxide solution
• 2 M ammonium hydroxide solution
• 2 M lead (ii) nitrate solution
• 2 M nitric (IV) acid

MARKING SCHEME

You are provided with the following:

• 3.3g metal carbonate, MCO₃ , labeled solution Q
• 2M hydrochloric acid, labeled solution P
• Sodium hydroxide, labeled solution R containing 40g/L of solution
• You are required to determine the relative atomic mass of metal M
  
  Procedure
  1. Measure accurately 100cm³ of solution P into clean 250cm³ conical flak and add all the 3.3g of solid Q, MCO₃
  2. Shake the mixture well and wait for effervescence to stop. Label the resulting solution as S
  3. Pipette 25cm 3 of solution R into a conical flask and add 2-3 drops of phenolphthalein indicator.
  4. Fill the burette with solution S and titrate against the solution R until the end point.
  5. Record your results in the table below. Repeat the procedure at least two times to complete the table.
     (4 mks)
     USE THE STUDENT'S VALUE (ASSUMING A.V = 20 cm³)
     

     	i	ii	iii
     Final burette reading ( cm3)	20.0	40.0	20.1
     Initial burette reading (cm 3)	0.0	20.0	0.0
     Volume of solution S used (cm3)	20.0	20.0	20.1

     
     
     1. What is the average volume of solution S used? (1mk)
        20.0 + 20.0 + 20.1  = 20.0cm³
                         3
     2. Calculate the moles of sodium hydroxide, solution R used. (2mks)
        40g  = 1M                                
        40
        1 mole = 1000cm³
        X moles^x = 25cm³
           X =  1 x 25
                   1000
                                               = 0.025 moles
     3. Calculate the moles of hydrochloric acid in the average volume of solution S used. (2mks)
        NaOH(aq) + HCL(aq) → NaCl(aq) + H20(1)
        NaOH:HCL
                1:1
        0.025:0.025                   = 0.025 moles
     4. Calculate the moles of hydrochloric acid in 100cm3 of solution S. (2mks)
        0.025 moles = 20 cm^3\
        X moles    =   100cm³
        
        0.025 x 100      =  0.125 moles
                 20
     5. Calculate the moles of hydrochloric acid in the 100cm3 of the original solution P. (2mks)
        2 moles = 1000cm³
        x moles = 100cm³
        x = 2 x 100
                1000                 =   0.2 moles
     6. Calculate the moles of hydrochloric acid, solution P that reacted with solid Q, MCO₃. (2mks)
        0.2 moles = 0.125 moles
                        = 0.075 moles
     7. Calculate the moles of MCO³ that reacted. (2mks)
        MCO₃(S) + 2HCL(aq) → MCL₂(aq) + CO₂(g) + H₂O(l)
        
        = 0.075 = 0.0375 moles
               2
     8. Calculate the relative formula mass (RFM) of MCO₃. (2mks)
        Moles = mass
                      RFM
        0.0375 = 3.3
                        x
        x =    3.3
              0.0375
        x = 88
     9. Calculate the relative atomic mass (RAM) of metal M. (1mk)
           88 = MCO₃
           88 = M + 12 + 48
           88 = M + 60 – 60
        – 60
                 M = 28
                 M = 40