Demonstrate knowledge and understanding of the preparation of insoluble salts by precipitation Suggest a method of making a given salt froma suitable starting material, given appropriateinformation

1. Presented by: Mrs. Saia

2. Review last lesson
Preparing soluble salts
 A pure, dry sample of a soluble salt can be prepared in two ways.
1 Method one
 add excess insoluble substance (base) to warm acid
 filter off excess base
 evaporate filtrate to half volume
 cool to allow crystals to form
 filter off the crystals
2 Method two
 add alkali to acid, or vice versa, in the presence of an indicator
until the indicator changes colour
 repeat the process without the indicator, or remove the indicator
using charcoal
 evaporate the solution to half volume
 cool to allow crystals to form
 filter off the crystals
 You can dry the crystals by placing it in a desicator, in a low
temperature oven, or between two sheets of filter paper.

3. Objectives
 Demonstrate knowledge and
understanding of
the preparation of insoluble salts by
precipitation
 Suggest a method of making a given
salt from
a suitable starting material, given
appropriate
information

4.  To make an insoluble salt, two soluble salts need to
react together in a precipitation reaction.
 For this purpose we need to know which salts are
soluble and which are insoluble
 All nitrates are soluble
 All sodium, potassium and ammonium salts are
soluble
 All chlorides are soluble except lead and silver
 All sulfates are soluble except lead, calcium and
barium
 All carbonates are insoluble except sodium
potassium and ammonium

5. Insoluble salt
 Using information
from prevoius slide
lets find out if the
salt is soluble or not
 Sodium chloride
 Magnesium sulfate
 Ammonium nitrate
 Lead chloride
 Silver nitrate
 Calciun carbonate
 Potassium sulfate
 Barium chloride
 Iron sulfate
 Barium sulfate
 Lead nitrate
 Ammonium chloride
 Calcium chloride

6. Choosing the reactants/reagent
 We can see that silver chloride is an
insoluble salt. It can be made by reacting a
soluble silver salt with a soluble chloride
salt.
 Which silver salt is soluble?
 Silver nitrate
 Which soluble chloride we may use
 Many: NaCl, MgCl2, HCl and any of chloride
except a few , one we just want to make

7. Making silver chloride
 Silver nitrate and sodium chloride are both soluble. When
their solutions are mixed together, soluble sodium nitrate
and insoluble silver chloride are made:
 silver nitrate + sodium chloride → sodium nitrate + silver
chloride
AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s)
 The reaction just takes place between silver and
chloride ions actually to make silver chloride insoluble
salt.
 The silver chloride appears as tiny particles suspended in
the reaction mixture - this is the precipitate. The
precipitate can be filtered, washed with water on the filter
paper, and then dried in an oven.

8. Method
 Mix together two
suitable solutions (see
above).
 Use filtration to separate
the precipitate as a
residue from the
solution.
 Wash the precipitate
with distilled water while
it is in the filter funnel.
 Leave the washed
precipitate aside or in a
warm oven to dry.
 it with distilled water.
 Reasons for each step
 Filtration separates
insoluble substances
from liquids and
solutions.
 The precipitate is
insoluble in water, so
any remaining
contaminating solution
can be removed by
washing

9. Making silver chloride
 Mix together two
suitable solutions.
 Use filtration to separate
the precipitate as a
residue from the
solution.
 Wash the precipitate
with distilled water while
it is in the filter funnel.
 Leave the washed
precipitate aside or in a
warm oven to dry.
 it with distilled water.

10. What is Precipitation
Reaction
 A chemical reaction occurring in an
aqueous solution where two ions from two
different solutions combine, resulting in
the formation of an insoluble salt”.
 These insoluble salts formed in precipitation
reactions are called precipitates. Precipitation
reactions are usually double displacement
reactions involving the production of a solid
form residue called the precipitate. These
reactions also occur when two or more
solutions with different salts are combined,
resulting in the formation of insoluble salts that
precipitate out of the solution.

11. Examples of precipitation
 Some more examples of chemical equations of on
precipitation reaction are as below
 AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)
 MgCl2(aq) + Na2CO3(aq) → MgCO3(s) + 2NaCl(aq)
 Chemistry of precipitation reactions
These reactions are called double displacement
reactions where ions of two soluble salts displace
each other
AB + CD → CB + AD

12. Understanding ionic equations
 AB(aq) + CD(aq) → AD(aq) + CB(s)
 A+(aq) + B-(aq) + C+(aq) + D-(aq) → A+(aq) + D-(aq) + CB(s)
C+ (aq)+ B- (aq) → CB (s)