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
(962°C), high density (10.49 g cm-³), 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. ___________________________________________
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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. ______________
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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.
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[1]
What energy change occurs in the endergonic process of electrolysis?
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[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-²) from a light source; i.e., S = k × D-² + c'; the Table shows a
summary of the chosen conditions and raw data.
Constants: photographic paper "X" (36 cm²); 30 W fluorescent light;
standard grey colour (Munsell 6); ambient temperature (17°C); distance
(D) measured from light bulb side-surface to paper.
Distance (D) / mm |
45 |
58 |
71 |
84 |
97 |
97 |
97 |
Distance-² (D-²) / m-² |
|
|
|
|
|
|
|
Time (t) / s |
144 |
185 |
214 |
236 |
232 |
254 |
249 |
Speed (S) / ms-¹ |
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-¹ _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
40_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
\|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
0 _/|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
| | | | | | |
0 100 200 300 400 500 600
Distance-² (D-²) / m-²
(b) Calculate the values for the inverse-square of the distance (D-²),
and insert these data in the Table.
[3]
Plot a (second) graph, with the inverse-square of distance (D-²) 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-² + c. ______________________________________________________
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[2]
Construct a precisely worded conclusion for the inverse-square of
distance (D-²) as the independent variable. ___________________________
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