METALS: SILVER
Silver, which is extremely rare in the Earth's crust (0.000007%), is
usually found in ores either as a sulfide or native. This element is a
typical transition metal, as evinced by its (fairly) high melting point 
(962C), high density (10.49 g cm-), variable oxidation states [e.g., 
(colourless) Ag(I) and (coloured) Ag(II)], and catalytic activity 
(e.g., it is used in the oxidation of ethene to ethane-1,2-diol).
[.. K > Ca > Na > Mg > Al > Zn > Fe > Sn > Pb > (H) > Cu > Hg > Ag ..]
1. One of several methods of extracting silver from low-grade ores involves heating silver(I) sulphide in air. Construct a symbol equation for this extractive method. ___________________________________________ _______________________________________________________________________ [2] 2. Silver is highly resistant to corrosion by atmospheric oxygen. However, silver slowly 'tarnishes' in the presence of either sulfur or compounds of sulfur; the corrosion product is known as silver tarnish (Ag2S). One method of removing this tarnish from a silver object is to rub its surface with aluminium (whose oxide layer has been removed by suspension in aqueous sodium chloride). Construct the symbol equation for this unusual application of a displacement reaction. ______________ _______________________________________________________________________ [2] 3. Silver's attractive appearance, high resistance to corrosion, and high electrical conductivity has resulted in its extensive use as an electroplating metal. In silver-electroplating, the object to be plated is made the cathode of an electrolysis cell which contains a silver anode and an electrolyte of aqueous silver(I) nitrate. Write an ionic equation for the reaction which occurs at the cathode. _______________________________________________________________________ [1] What energy change occurs in the endergonic process of electrolysis? _______________________________________________________________________ [2] 4. Silver(I) halides are photosensitive (a property which is exploited in black-and-white photography and in photochromic lenses); e.g., the exposure of silver(I) bromide to light energy results in photolysis:
What energy change occurs in the endergonic process of photolysis?  
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5.  White photographic paper, containing silver(I) bromide, darkens on
exposure to light as black metallic silver particles are formed. A 
chemist, who was researching new types of 'photo-paper', investigated
two related hypotheses: 'The speed (S) at which photographic paper "X"
darkens to standard grey colour decreases in linear proportion to the
distance (D) from a light source; i.e., S = k  D + c', and 'The speed
(S) at which photographic paper "X" darkens to standard grey colour
increases in linear proportion to the inverse square of the distance
(D-) from a light source; i.e., S = k  D- + c'; the Table shows a
summary of the chosen conditions and raw data.
Constants: photographic paper "X" (36 cm); 30 W fluorescent light; standard grey colour (Munsell 6); ambient temperature (17C); distance (D) measured from light bulb side-surface to paper.
 Distance (D) / mm
  45 
  58 
  71 
  84 
  97 
  97 
  97 
 Distance- (D-) / m-
 
 
 
 
 
 
 
 Time (t) / s
 144 
 185 
 214 
 236 
 232 
 254 
 249 
 Speed (S) / ms-
  69 
  54 
  47 
  42 
  43 
  39 
  40 


(a) Plot a graph, with distance (D) as the independent variable, and 
then draw a best curve through as many points as is sensible.
                                                                    [3]
Construct a precisely worded conclusion for distance (D) as the 
independent variable. _________________________________________________
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                             Distance (D) / mm
         0        50        60        70        80        90       100
         |         |         |         |         |         |         |
      70_|/\/|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
        _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
        _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
        _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 S      _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 p    60_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 e      _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 e      _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 d      _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
        _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
(S)   50_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
        _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 /      _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
        _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 ms-   _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
      40_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
        _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
        _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
          \|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
       0 _/|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
         |         |         |         |         |         |         |
         0       100       200       300       400       500       600
                           Distance- (D-) / m-
     
(b) Calculate the values for the inverse-square of the distance (D-),
and insert these data in the Table.
                                                                    [3]
Plot a (second) graph, with the inverse-square of distance (D-) as the
independent variable, and then draw a best straight line through as 
many points as is sensible.
                                                                    [3]
Determine the gradient of this second graph; this value, 'k', is the
proportionality constant in the linearly proportional relationship
S = k  D- + c. ______________________________________________________
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                                                                    [2]
Construct a precisely worded conclusion for the inverse-square of 
distance (D-) as the independent variable. ___________________________
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