Chemistry Reference
In-Depth Information
voltage when the hydrogen on one electrode reacts
with the oxygen on the other by the transfer of
electrons through the external circuit.
R
●
Decomposition of sodium chlorate(i),
i
), catalysed by
a cobalt(ii)
ii
) salt.
2NaClO(
aq
) → 2NaCl(
aq
) + O
2
(
g
)
Use the same apparatus as in the previous exercise
to obtain data on the volume of oxygen evolved
against time. This can be analysed to investigate the
effect of concentration on the reaction rate and on
the volume of product.
●
Identical mixtures of sodium thiosulfate solution
and hydrochloric acid are used at different
temperatures in the experiment described on
p. 107. The results illustrate how rate depends
on temperature when the concentrations are kept
constant.
●
Compare a silver halide that has been exposed
to light with a sample kept in the dark. Prepare a
suspension of silver bromide and divide it into two
portions. Wrap one portion in aluminium foil and
hold the other near a bright light.
●
Divide a mixture of bromine and hexane into two
portions. Expose one to bright light while the
other is kept in the dark. Only the sample exposed
to the light will evolve hydrogen bromide, and its
brown colour will fade.
●
Biology-type experiments on green leaves and
light. It is probable that the students will already be
familiar with these.
●
The effect of enzymes on the decomposition of
hydrogen peroxide. Add a piece of raw liver to
20 vol hydrogen peroxide.
●
Add a few drops of washing-up liquid to 20 vol
hydrogen peroxide. Divide this mixture into two
portions and add manganese(
iv
) oxide to one
portion. Compare the rate of decomposition of
hydrogen peroxide in the two samples.
Chapter 7 Chemical reactions
●
Reaction of calcium carbonate and acid
(Figure 7.3, p. 105) - the effect of concentration
and surface area.
●
Reaction of sodium thiosulfate and acid
(Figure 7.8, p. 107) - the effect of concentration.
●
Decomposition of hydrogen peroxide, catalysed by
manganese(
iv
) oxide - the effect of concentration
and mass of catalyst on the rate and on the volume
of product.
First use a mixture of 2 cm
3
of 20 vol hydrogen
peroxide and 48 cm
3
of water, with 0.2 g of
manganese(
iv
) oxide. Then use a mixture of 4 cm
3
of 20 vol hydrogen peroxide and 46 cm
3
of water
with 0.2 g of manganese dioxide. Finally use a
mixture of 2 cm
3
of 20 vol hydrogen peroxide and
48 cm
3
of water with 0.4 g of manganese dioxide.
Collect the oxygen over water in an inverted
measuring cylinder or burette and obtain sets of
readings of volume against time.
●
Add a 2 cm length of magnesium ribbon to an
excess of 2 mol dm
−3
hydrochloric acid and measure
the time taken for the metal to react. Repeat, with
the same sized piece of magnesium but a different
concentration of acid. (Another version of this
experiment is to make temperature the variable and
use hydrochloric acid at different temperatures.)
●
Add a 2 cm length of magnesium ribbon to an
excess of 2 mol dm
−3
ethanoic acid. Measure the
time taken for the metal to react and compare this
result with the one above.
●
Reaction of metal and acid - the effect of
concentration and surface area on the reaction rate
and on the volume of product.
Collect the hydrogen and obtain data on the
volume evolved against time. The apparatus used
could be a flask with delivery tube and a gas syringe
or burette. A length of magnesium ribbon is
suspended above excess acid and is allowed to fall
into the acid as the timing starts.
The experiment could be repeated using different
lengths of ribbon and different concentrations of
acid. Also, a mass of magnesium powder equal to
that of the ribbon could be suspended above the
acid in a small tube.
Chapter 8 Acids, bases and salts
Acids and alkalis
●
With simple indicators, find the acid colour, the
alkaline colour and the neutral colour. Hold the acid
tube and the alkaline tube up to a light together and
look through both to see the neutral colour.
●
Dilution experiments using universal indicator
and 0.1 mol dm
−3
solutions of hydrochloric acid,
sodium hydroxide, ethanoic acid and ammonia.
These will establish the pH scale and promote an
understanding of the distinction between strong
and weak electrolytes.
