IGCSE chemistry
Preparation of salts
Salts
Ionic substances which consists of a positive ion (e.g. metal ion or ammonium ion) and a negative ion
(eg non-metal ion or non-metal ion radical) most of which have a pH of 7 and which, when molten or
dissolved, conduct electricity. Most salts are soluble in water except a few as shown in the table below.
Acids
Bases
Soluble
Insoluble
All common acids
The alkalis
All other bases
All nitrates
All chlorides except
Silver chloride, lead chloride
All sulphates except
Salts
Sodium and potassium carbonates
All ammonium salts
Barium sulphate, lead sulphate,
calcium sulphate is slightly soluble
All other carbonates
How do we make samples of pure dry crystals of a salt. The flowchart below will help you to identify the correct method
no
Is salt
soluble?
yes
Base
soluble?
no
yes
1. For each of the following salts: decide which method you will use to make the salt and select
suitable chemicals;
Salt you are going to
make
Starting chemicals you will use
The method you will use
magnesium sulfate
sodium nitrate
calcium chloride
barium chloride
ammonium nitrate
copper ethanoate
2. This question is about preparing insoluble salts.
(a) Complete the table below about he making of insoluble salts
1.
2.
3.
4.
5.
salt
copper carbonate
silver chloride
lead sulphate
lead chloride
barium sulphate
starting chemicals
(b) For each of the above examples (i) write a chemical equation and (ii) an ionic equation.
3. Add these captions in the correct boxes on the flowchart.
Precipitation
Neutralization (Acid + excess base/metal)
- Make solutions containing ions of salt to
be made (need soluble salts)
- Add the solutions
- Filter off precipitate
- Wash precipitate with distilled water
- Dry with filter paper or on warm gauze
- Add excess base/metal to acid until no
more dissolves (warm acid if necessary)
- filter off excess base/metal
- obtain salt from solution (see below)
Indicator method/titration
Obtaining dry salt from solution
- Add acid via burette to alkali` + indicator
until neutral ( or until temperature stops
rising)
- Measure volume of acid added; throw
away solution;
- Add same volume of acid to same
amount of alkali without indicator
- Obtain dry salt from solution
- Concentrate solution until it becomes
saturated which is done by driving off
most of the water by heating it. Solution
is saturated when crystals form on a
glass rod dipped in the solution.
- Stop heating and allow solution to cool
- Crystals can be washed with distilled
water
- Dry crystals with filter paper or place on
warm gauze or in warm place
4. Complete the following symbol and word equations of neutralization reactions (you will need to
balance the symbol equations):
⎯→
a. HCl (aq)
+
MgO (s)
b. H2SO4 (aq)
+
KOH (aq) ⎯→
c. HNO3 (aq)
+
NH4OH (aq) ⎯→
d. C2H3OOH(aq)
e. HNO3 (aq)
NaOH (aq) ⎯→
+
+
Ca(OH)2 (aq) ⎯→
f. sulfuric acid (aq) +
copper oxide (s) ⎯→
g. hydrochloric acid (aq) +
lithium oxide (s) ⎯→
h. nitric acid (aq) + copper oxide (s) ⎯→
i.
⎯→
CaSO4 (aq)
+
H2O (l)
j.
⎯→
ZnCl2 (aq)
+
H2O (l)
5. The diagram below shows some reactions of dilute sulfuric acid. Use it to answer the questions
below.
magnesium ribbon
copper (II) oxide
magnesium sulfate solution + gas A
blue solution B
sodium hydrogen carbonate
sulfuric acid
sodium sulfate solution + gas C
substance D
substance D goes red
solution E
potassium sulfate solution only
Name or give the formula of each of the following :
(a)
(b)
(c)
(d)
(e)
gas A:
solution B:
gas C:
substance D:
solution E: