C5h Ionic Equations (and precipitation reactions)
• A precipitation reaction involves two solutions reacting together to make an
e.g. consider barium chloride and magnesium sulphate:
We use barium chloride
to test for sulphate
ions in water
(look back to C4)
• In a solid the ions are held in ___________ positions and cannot _________ but
when they are molten or in solution the ions are _________________________.
• If 2 solutions are mixed the ions from one solution can _____________ with the
ions from another solution and they may react. If the reaction produces an
________________ solid it will look cloudy. We call this a ________________.
Higher • Most precipitation reactions are extremely _________ reactions between
Using Nitrate Solutions to test for Halide and Sulphate Ions
1. We can use silver nitrate, AgNO3 or Lead nitrate, Pb(NO3)2 to test for chloride,
bromide and iodide ions (Cl-, Br-, I- ).
Halide name Halide Ion Colour of precipitate
sodium + silver silver + sodium
chloride nitrate chloride nitrate
Using the formulae of the ions in the table, construct balanced ionic equations for
- - - -
Na+ Cl Ag+ NO3 Br I
1. Write out a balanced symbol equation with STATE SYMBOLS for the first word
2. Now write out the ions for any aqueous solutions (aq) in question 1.
3. Some ions appear unchanged on both sides of the equation. They are called
“spectator ions”. Underline the spectator ions in the equation in question 2.
4. Now rewrite the equation in question 2 without spectator ions – this is what we call
an IONIC equation:
Repeat Qu 1-4 for each of the word equations on separate paper
2. Barium nitrate tests for sulphate ions to produce a white precipitate (barium
chloride can also be used).
barium nitrate + potassium sulphate
barium chloride + potassium sulphate
Higher Ionic Equations
Preparation of an insoluble salt using precipitation
The preparation of lead (II) iodide
You must be able to:
• Label the apparatus used during the preparation of an insoluble compound by
• Describe the stages involved in the preparation of a dry sample of an insoluble
compound by precipitation (you will be given the names of the reactants)
1. mix solutions of reactants (in an exam you must use their names)
2. _____________ off the solid
3. wash the __________ (solid left in the filter paper) with __________
4. dry the solid residue e.g. in a warm oven