Chemistry Reference
In-Depth Information
their oxides, such as the hydroxides of iron, lead
and copper.
●
Action of heat on nitrates. For safety reasons this
is best demonstrated as there are some serious
hazards - molten potassium and sodium nitrates/
nitrite, decrepitation with lead nitrate and the
emission of the poisonous gas, nitrogen dioxide.
●
Action of heat on carbonates - see p. 152.
addition of dilute nitric acid the hydroxide will
reappear, only to dissolve with the addition of more
nitric acid.
OH
−
OH
−
metallic cation L
metal hydroxide L metallic anion
H
+
H
+
Equilibria
●
Ice/water and other changes of state.
●
Saturated solutions in equilibrium with excess
solute.
●
Bismuth chloride and water. Prepare a solution of
bismuth chloride in the minimum of hydrochloric
acid and add to a large excess of water.
BiCl
3
+ H
2
O
L
BiOCl(
s
) + 2HCl
white
On the addition of hydrochloric acid, the white
precipitate will become fainter and then disappear.
The addition of sodium hydroxide solution will
cause the precipitate to reappear. This illustrates
different positions of the same equilibrium.
●
Iodine will react with chlorine to form iodine
monochloride, and with an excess of chlorine the
following equilibrium will be established.
Cl
2
+ ICl(l)
l
)
L
ICl
3
(
s
)
brown yellow
The removal of chlorine by blowing air through the
U-tube or by inverting it results in the formation
of the brown liquid, while the addition of chlorine
results in the formation of the yellow solid.
●
Fe
3+
(
aq
) + Ag(
s
)
L
Fe
2+
(
aq
) + Ag
+
(
aq
)
●
FeCl
3
+ 3KCNS
L
Fe(CNS)
3
+ 3KCl
Although this equation is not strictly correct, at this
level it is preferable to the ionic equation involving
FeCNS
2+
.
●
N
2
O
4
L
2NO
2
Altering the temperature using ice-water or hot
water will change the position of equilibrium
and illustrate its dependence on the exothermic
or endothermic nature of the reaction. Similarly,
changing the pressure by compressing a sample of
the equilibrium mixture in a gas syringe will also
move the position of equilibrium.
●
NH
4
Cl
L
NH
3
+ HCl
Heat ammonium chloride to show the influence of
temperature on the position of equilibrium.
Rusting of iron
●
Experiment on rusting as described in the text
(Figure 10.20, p. 162).
R
●
Set up a cell with two iron electrodes connected
through a voltmeter and bubble oxygen onto one
electrode. From the polarity of the cell, students
can deduce the direction of the electron flow
and analyse the cell reactions in terms of electron
transfer.
R
●
Set up a zinc/iron cell to demonstrate sacrificial
protection. Analyse the cell reactions as above.
R
Chapter 11 Air and water
Air
●
Find the percentage of oxygen in the air as
described in the text (Figure 11.6, p. 174).
Ammonia gas
●
Laboratory preparation of ammonia (Figure 11.16,
p. 179).
●
The fountain flask experiment (Figure 11.18,
p. 180).
●
Show that ammonia is a base. Neutralise acids by
adding 2 mol dm
−3
aqueous ammonia to dilute
acids in the presence of universal indicator.
●
Show that ammonia is a weak base. Measure the
pH of 0.1 mol dm
−3
aqueous ammonia and its
conductivity. Compare the pH and conductivity
with those of 0.1 mol dm
−3
sodium hydroxide.
●
Precipitation of metal hydroxides - see Chapter 10.
●
Test for the ammonium ion (p. 262).
Reversible reactions
●
Acid/base indicators.
●
Action of heat on copper(ii)
ii
) sulfate-5-water.
●
Add sodium hydroxide solution to a solution of a
zinc, an aluminium or a lead salt. The hydroxide
will precipitate and then dissolve in excess alkali to
form an aluminate, zincate or plumbate. On the
