C5h Ionic Equations (Precipitation Reactions)

C5h Ionic Equations (and precipitation reactions)

A precipitation reaction involves two solutions reacting together to make an insoluble solid

e.g. consider barium chloride and magnesium sulphate:

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 ________________.

Most precipitation reactions are extremely _________ reactions between ions

Higher

IMPORTANT

We use barium chloride to test for sulphate ions in water

(look back to C4)

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 precipitatechloridebromideiodide

Word equations:

sodium + silver silver + sodium chloride nitrate chloride nitrate

HIGHER ONLYUsing the formulae of the ions in the table, construct balanced ionic equations for the reactions

1. Write out a balanced symbol equation with STATE SYMBOLS for the first word equation above.

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:

Na+ Cl- Ag+ NO3- Br- I-

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).

Word equations

barium nitrate + potassium sulphate

barium chloride + potassium sulphate

Ionic EquationsHigher

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 precipitation.

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)

Method1. 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