waecE-LEARNING
Physics Paper 2, Nov/Dec. 2012  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
General Comments
Weakness/Remedies
Strength
















Question 6

  Question 6
When a steady current of 1.57A is passed through a copper voltameter for 20.0 minutes, a mass of 0.625 x 10-3 kg of copper is deposited on the cathode.  Calculate the relative atomic mass of copper.
(1 F  96500 C)

 

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comments

    This question was poorly attempted as most respondent candidates were not able to relate the mass of copper deposited to the quantity of charge passed through the voltameter and then the amount of charge required to deposited a mole of copper.

  ml   =  mr =
    Q l     Q r
[Q1  =  lt]
Q r =  2  x  96500 C

mr =  0.625  x  10-3  x  2  x  96500
                      1.57  x  20  x  60
    
    =      0.064 kg

 

The expected answer is
Q         =          It                                                                                                        
            =          1.57 x 20 x 60
            =          1884C                                                                                                
                                                                                     OR
            1884 C            0.625 x 10-3
            12 x 96500 C              2 x 96500 x 0.625 x 10-3                                                          
                                                            1884

                                    0.064 kg                                                                                 


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