"Preparation of Salts Chemistry Worksheet"

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CHEMISTRY Class Notes
Preparation of Salts
Name: _____________________ (
)
Class: ___________
Date: ________________
Preparation of Salts
When preparing a salt, two factors to consider:
1. Is the salt soluble in water?
2.
Are the starting materials soluble in water?
There are 3 methods of preparing salts.
1. Precipitation reactions
2. Reactions between acids and excess
a. insoluble metal
b. insoluble base
c. insoluble carbonate
3. Reactions between acids and alkalis/carbonate solutions (Titration)
1
CHEMISTRY Class Notes
Preparation of Salts
Name: _____________________ (
)
Class: ___________
Date: ________________
Preparation of Salts
When preparing a salt, two factors to consider:
1. Is the salt soluble in water?
2.
Are the starting materials soluble in water?
There are 3 methods of preparing salts.
1. Precipitation reactions
2. Reactions between acids and excess
a. insoluble metal
b. insoluble base
c. insoluble carbonate
3. Reactions between acids and alkalis/carbonate solutions (Titration)
1
CHEMISTRY Class Notes
Preparation of Salts
Precipitation
1.
(the only method to prepare insoluble salts)
· Salt to prepare is an insoluble salt in solution, both reagents are aqueous solutions.
a) Starting materials for making lead(II) sulfate can be: lead(II) nitrate and sulfuric acid.
Word equation: lead(II) nitrate + sulfuric acid à lead(II) sulfate + nitric acid
(aq) à PbSO
Chemical equation: Pb(NO
)
(aq) + H
SO
(s) + 2HNO
(aq)
3
2
2
4
4
3
b) Add the reagents together and keep stirring until no more precipitation forms.
c) Filter the mixture to get the residue.
d) Wash the residue with distilled water to remove impurities.
e) Dry on a piece of filter paper to obtain the pure sample.
2. Acid + Insoluble Metal
(to prepare soluble salts)
· For moderately reactive metals like magnesium, aluminium and zinc.
· Not for unreactive metals like Cu and Ag.
· Not for very reactive metals like K, Na and Ca.
a) Starting materials for making zinc sulfate can be: zinc and sulfuric acid.
Word equation: zinc + sulfuric acid à zinc sulfate + hydrogen
(aq) à ZnSO
Chemical equation: Zn (s) + H
SO
(aq) + H
(g)
2
4
4
2
b) Add excess zinc to sulfuric acid until there is no more effervescence.
Reason: To ensure a complete reaction and all sulfuric acid has been used up, so that it
will not contaminate the desired solution.
c) Filter off the excess zinc (insoluble metal).
Reason: To ensure that the unreacted zinc will not contaminate the salt formed.
d) Heat the filtrate to saturate the zinc sulfate salt solution. Do not heat to dryness.
Reason: By heating to dryness, the salt loses its water of crystallization and crystals will
not form.
e) When filtrate is saturated, let it cool and crystallize.
f) Wash the zinc sulfate crystals with distilled water dry between pieces of filter paper.
3. Acid + Insoluble Base
(to prepare soluble salts)
a) Starting materials for making copper (II) sulfate can be: copper(II) oxide and sulfuric
acid.
Word equation: Copper(II) oxide + Sulfuric acid à Copper (II) Sulfate + Water
(aq) à CuSO
Chemical equation: CuO (s) + H
SO
(aq) + H
O (l)
2
4
4
2
b) Add excess copper(II) oxide to sulfuric acid until there is no more reaction.
Reason: To ensure a complete reaction and all sulfuric acid has been used up, so that it
will not contaminate the desired solution.
2
CHEMISTRY Class Notes
Preparation of Salts
c) Filter off the excess copper(II) oxide (insoluble).
Reason: To ensure that the unreacted copper(II) oxide will not contaminate the salt
formed.
d) Heat the filtrate to saturate the copper sulfate salt solution. Do not heat to dryness.
Reason: By heating to dryness, the salt loses its water of crystallization and crystals will
not form.
e) When filtrate is saturated, let it cool and crystallize.
f) Wash the copper sulfate crystals with distilled water dry between pieces of filter paper.
4. Acid + Insoluble Carbonate
(to prepare soluble salts)
a) Starting materials for making magnesium chloride can be: magnesium carbonate and
hydrochloric acid.
Word equation: magnesium carbonate + hydrochloric acid à carbon dioxide + water +
magnesium chloride
(s) + 2HCl (aq) à CO
Chemical equation: MgCO
(g) + H
O (l) + MgCl
(aq)
3
2
2
2
b) Add excess magnesium carbonate to hydrochloric acid until there is no more reaction.
Reason: To ensure a complete reaction and all hydrochloric acid has been used up, so
that it will not contaminate the desired solution.
c) Filter off the excess magnesium carbonate (insoluble).
Reason: To ensure that the unreacted magnesium carbonate will not contaminate the
salt formed.
d) Heat the filtrate to saturate the magnesium chloride salt solution. Do not heat to
dryness.
Reason: By heating to dryness, the salt loses its water of crystallization and crystals will
not form.
e) When filtrate is saturated, let it cool and crystallize.
f) Wash the magnesium chloride crystals with distilled water dry between pieces of filter
paper.
5. Titration (acid with alkali or soluble carbonate solution)
(to prepare soluble salts)
· Salt to prepare is a soluble salt & both reagents are also soluble (aqueous solutions).
· Useful for preparing potassium, sodium and ammonium salts.
a) Starting materials for making sodium nitrate: sodium hydroxide and nitric acid.
Word equation: sodium hydroxide + nitric acid à sodium nitrate + water
(aq) à NaNO
Chemical equation: NaOH (aq) + HNO
(aq) + H
O (l)
3
3
2
b) Run a titration of the two reagents. One reagent will be in conical flask and the other
will be in the burette, using an indicator.
c) Once the end point is reached, the indicator will change colour, stop the titration and
record down the readings.
3
CHEMISTRY Class Notes
Preparation of Salts
d) Take 2 or more readings to get a definite titration volume.
e) Run the titration for one more time without using an indicator.
f) Heat the solution to saturate the sodium nitrate salt solution. Do not heat to
dryness.
g) When filtrate is saturated, let it cool and crystallize.
h) Wash the sodium nitrate crystals with distilled water dry between pieces of filter
paper.
4