A catalyst is defined as 'a substance which increases the rate of a 
chemical reaction, but which is itself chemically unchanged at the end
of the reaction'. Although many substances have catalytic activity
attributed to them, because they speed up chemical reactions, the
absence of permanent chemical change is often assumed ...
Zinc is a better reducing agent than hydrogen, and so displaces this less reactive element from its compounds; e.g.,
Because the above reaction is too slow to be useful as a convenient 
laboratory preparation of dihydrogen, a few drops of aqueous copper(II) 
sulfate are often added to increase the speed of reaction; and so the 
preparative method is usually described by this equation:
However, as the aqueous sulfate ions are spectators in this reaction 
mixture, and as zinc is also a better reducing agent than copper, there
will be (at least) two competing reactions; i.e.,
In principle, because copper(II) ions are better oxidizing agents than 
hydrogen ions, zinc should preferentially displace copper; if this is 
so, then the method might be better described by this equation:
Although this description is supported by the presence of copper powder
at the end of the reaction, alternatives are feasible - particularly 
when one considers the possible involvement of copper(I) ions.
[.. K > Ca > Na > Mg > Al > Zn > Fe > Sn > Pb > (H) > Cu > Hg > Ag ..]
1. One consequence of the above definition is that a catalyst has no effect on the yield of products (i.e., the position of equilibrium in a closed system). Although the laboratory preparation of hydrogen gas is normally executed in an open system, the yield does appear to decrease as the amount of copper(II) ions increases. To examine quantitatively this effect, the following hypothesis was investigated: 'For the reaction of zinc with dilute sulfuric acid, the volume (V) of hydrogen gas evolved decreases in linear proportion to the amount (M) of aqueous copper(II) ions added; i.e., V = k × M + c'; the Table shows a summary of the chosen conditions and raw data (no duplicate experiments were executed).
Constants: zinc granules (0.260 g = 4.00 mmol); aqueous sulfuric acid (1.00 mol dm-³; 100 cm³); aqueous copper(II) sulfate (1.00 mol dm-³); room temperature (298 K) and pressure (100 kPa); thermostatted water- bath; hydrogen gas collected with a 100 cm³ gas syringe.
 Amount of Cu2+ added (M) / mmol
 Volume of H2 evolved (V) / cm³
(a) Noting that hydrogen gas was evolved in these experiments, suggest 
one important safety precaution adopted. ______________________________
(b) Suggest one reason why higher values of the independent variable
were not examined. ____________________________________________________
Explain what would happen to the values of the dependent variable if,
during the investigation, the temperature increased (but the pressure
remained constant). ___________________________________________________

(c) Plot all five data points, and then draw the best straight line.
          _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
  V      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
  o   90_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
  l      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
  u      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
  m      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
  e      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
  o      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
  f      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 gas     |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 (V)     |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
  /      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
 cm³  30_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
         |         |         |         |         |         |         |
         0        0.5       1.0       1.5       2.0       2.5       3.0
                   Amount of aqueous Cu(II) added (M) / mmol
Extrapolate this straight line to the vertical axis; the intercept on
this axis, which corresponds to the maximum volume of hydrogen gas that
can be obtained, is the value 'c' in the linearly proportional 
relationship V = k × M + c. ___________________________________________
Determine the gradient of the graph; this (negative) value, 'k', is the
proportionality constant in the linearly proportional relationship 
V = k × M + c. ________________________________________________________
Write a precisely worded conclusion based on the graph. _______________
(d) This linear relationship rearranges to M = (V - c) ÷ k. Determine
the amount of copper(II) ions which results in no hydrogen gas being 
evolved (i.e., V = 0 cm³), by using your values of 'k' and 'c' in this 
rearranged equation. __________________________________________________
(e) Experiments were also executed using different metals, but with a 
similar set of constants; the aqueous copper(II) ions were omitted. 
Thus, when 4.00 mmol of magnesium was used, instead of zinc, the same 
maximum volume of hydrogen gas was obtained. Explain briefly what 
theoretical volume of dihydrogen would be expected using 4.00 mmol of:
Cadmium _______________________________________________________________
Strontium _____________________________________________________________
Lithium _______________________________________________________________
Gallium _______________________________________________________________
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