METALS: CADMIUM
Cadmium, a very rare element in the Earth's crust (0.00002%), occurs
mainly as the sulfide or carbonate in zinc ores. Compounds of cadmium, 
in contrast to those of zinc, appear to have little or no biological 
rle; so, inevitably, cadmium(II) ions accumulate up the trophic levels
because very few living organisms have evolved methods for egesting or
excreting these ions. In addition, partly because of the observed and 
predicted similarities between zinc and cadmium ions, and partly 
because enzymes containing zinc(II) ions are ubiquitous, cadmium ions 
could be expected to affect diverse biochemical processes.
[.. K > Ca > Na > Al > Zn > Cd > Fe > Ni > Pb > (H) > Cu > Hg > Ag ..]
1. The extraction of cadmium from zinc ores is fairly complex, but the final process involves chemical reduction of aqueous cadmium sulfate with zinc (DE = -70 kJ mol-). For this redox reaction, construct the: symbol equation; redox half equations; and net ionic equation. ________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ [4] Use the net ionic equation to complete and label this energy level diagram. Energy ____ __________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __________________ __________________ __________________ __________________________________________________ Path of reaction [4] 2. Currently, the major use of cadmium is in rechargeable 'nicad' batteries. Explain the direction of electron flow when a Ni-Cd cell is in use (i.e., transducing chemical to electrical energy). _____________ _______________________________________________________________________ [2] 3. A research chemist investigated the following hypothesis: 'The speed (S) of the displacement reaction between cadmium and aqueous sulfuric acid increases in linear proportion to the temperature (T) of the acid; i.e., S = k T + c'; the Table shows a summary of the chosen conditions and raw data (no duplicate experiments were executed).
Constants: amount (0.050 mol) of cadmium granules (spheres with surface areas of 4.2 0.2 mm); concentration (1.00 mol dm-) and volume (75 cm) of aqueous sulfuric acid; absence of catalysts; thermostatted water-bath; room temperature (295 K) and pressure (100 kPa); volume of dihydrogen collected via a gas syringe (50 cm).
 Temperature (T) / K
  295  
  307  
  319  
  331  
  343  
 Reaction time (t) / s
   77 
   40 
   25 
   21 
   17 
 Reaction speed (S) / ms-
   13
 
 
 
 
(a) State one reason why higher values of the independent variable were
not examined. _________________________________________________________
                                                                    [1]
(b) Calculate the missing values for the dependent variable, and insert
these data into the above Table.
                                                                    [2]

(c) Label both axes, with the independent variable on the horizontal
axis (cela va sans dire?), and then plot the data points.
           _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
       60_|_|_|_ Aqueous |_|_|_|_|_|  Aqueous |_|_|_|_|_|_|_|_|_|_|_|
          |_| sulfuric acid  |_|_|_sulfuric acid  |_|_|_|_|_|_|_|_|_|
         _|_(1.00 mol dm-)_|_|_|(1.00 mol dm-) _|_|_|_|_|_|_|_|_|_|
          |_|_|_|  +  |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
       50_|_|_|  Cu(s)  |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_(0.001 mol) |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
         _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
       40_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
         _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
       30_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
         _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
       20_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
         _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
       10_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_| Aqueous |_|_|
         _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|  ethanoic acid  |
          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_| (2.00 mol dm-) |
        0_|/\/\/|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          |     |         |         |         |         |         |
          0    293       303       313       323       333       343
                            
                                                                    [4]
Draw a best straight line through as many points as is sensible, and
then determine the gradient of the (plotted) graph; this value, 'k', is
the proportionality constant in the linearly proportional relationship 
S = k  T + c. ________________________________________________________
_______________________________________________________________________
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                                                                    [2]
Write a precisely worded conclusion based on the (plotted) graph. _____
_______________________________________________________________________
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                                                                    [5]
(d) Sketch the graph that would be obtained if one of the constants was
changed separately, and explain why each of these graphs differs from 
that obtained for the set of constants shown with the Table.
Aqueous sulfuric acid (1.00 mol dm-) and copper (0.001 mol) __________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
                                                                    [3]
Aqueous ethanoic acid (2.00 mol dm-) _________________________________
_______________________________________________________________________
_______________________________________________________________________
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                                                                    [3]
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