Chemistry Reference
In-Depth Information
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Reaction of phosphorus and chlorine. Put a small
piece of white phosphorus on a spoon into a gas
jar of chlorine.
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Hydrogen and chlorine. Make a mixture of these
gases by electrolysis and expose it to a bright
light from a photographic flash or burning
magnesium.
to the aqueous nitrate of another metal. The
students look for evidence of displacement and so
establish an order of reactivity. Suitable metals are
magnesium, zinc, lead, copper and silver.
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Identifying metal ions
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Reactions of cations in aqueous solution with
sodium hydroxide - Al
3+
, Fe
2+
, Fe
3+
, Cu
2+
, Ca
2+
,
Zn
2
, Cr
3+
,. An excess of sodium hydroxide solution
is added slowly to a small volume of the solution
containing the cation. This is an exercise in
observation, organisational and recording skills and
in the ability to write chemical equations - word,
molecular and ionic.
●
Reactions of the same cations with aqueous
ammonia. This is essentially a repeat of the exercise
above but with less emphasis on equation writing.
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Identification of unknown cations using sodium
hydroxide solution and aqueous ammonia.
Metals
●
Most metals react with dilute acids. Add a small
piece of a metal to dilute hydrochloric acid and test
for hydrogen. Use magnesium, aluminium, zinc,
iron and copper.
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Differences in the physical properties of the
transition elements, such as melting points and
densities, can be established from data topics.
●
Transition metals react with oxygen to form
insoluble oxides that are not alkaline. The reactions
of these metals with acids will illustrate their lower
reactivity.
●
An observational exercise using compounds of
chromium, manganese, cobalt, nickel and copper
will emphasise that these metals have coloured
compounds.
●
Flame colours (p. 261).
Amphoteric hydroxides and oxides
●
Hydroxides are classified as basic or amphoteric.
The qualitative exercises above will provide a
practical basis for the underpinning theory. A useful
extension exercise is to provide unknown cations
in solution and for the students to ascertain if their
hydroxides are basic or amphoteric.
●
Another informative practical involves adding
dilute acid dropwise to an aluminate or zincate and
observing the changes in reverse.
Chapter 10 Metals
Typical reactions of metals
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Reaction of metals with dilute acids (p. 150).
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Reaction of metals with air and oxygen (p. 151).
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Reaction of metals with cold water or steam
(p. 151).
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OH
−
OH
−
Al
3+
L
Al(OH)
4
−
L
Al(OH)
3
H
+
H
+
Competition reactions
●
Reduction of metal oxides by other metals
(Figure 10.6, p. 154). Demonstrate the Thermit
reaction and the reactions between the metals
magnesium, zinc, iron and copper and their oxides.
This will establish an order of reactivity for these
metals. Some of these reactions are very violent so
the use of small quantities and a rehearsal before
the class demonstration are essential.
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Reduction of metal oxides by methane/hydrogen.
It is safer to use methane, which is passed over
heated copper oxide.
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Metal/metal displacement reactions in aqueous
solution. Clean pieces of a metal are added
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Oxides are classified as basic, acidic, neutral or
amphoteric. An exercise with unknown oxides is
conducted using the following tests:
●
Does the oxide dissolve in water? If so, measure
the pH.
●
Do the insoluble oxides react with 4 mol dm
−3
nitric acid?
●
Do the insoluble oxides react with 4 mol dm
−3
sodium hydroxide?
Action of heat on metal compounds
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Action of heat on metal oxides.
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Action of heat on hydroxides. It is easier to use
metal hydroxides that have a different colour from
