In this experiment, the similarities and differences in the solubilities of the halides of some Group 1 & 2 metals and silver are investigated using a microscale technique.

Class practical

In this experiment, the similarities and differences in the solubilities of the halides of some Group 1 & 2 metals and silver are investigated using a microscale technique.

Lesson organisation

This is a class experiment in which students can very quickly and simply investigate trends in the solubilities of halides of some metals on a microscale, using only drops of solution. The experiment should take about 10 minutes.

Apparatus Chemicals

Eye protection

Each working group requires:

Worksheet containing a grid on which drops of solution are combined

Clear plastic sheet such as OHP film

Access to solutions contained in plastic pipettes (Notes 1 and 2):

Calcium nitrate, 0.2 M

Lithium bromide, 0.2 M

Sodium fluoride, 0.2 M

Sodium chloride, 0.2 M

Potassium bromide, 0.2 M

Potassium iodide, 0.2 M

Silver nitrate, 0.1 M

Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Wear eye protection. 

Calcium nitrate solution, Ca(NO3)2(aq) - see CLEAPSS Hazcard.

Lithium bromide solution (similar to lithium chloride), LiBr(aq) - see CLEAPSS Hazcard. 

Sodium fluoride solution, NaF(aq) - see CLEAPSS Hazcard. 

Sodium chloride solution, NaCl(aq) - see CLEAPSS Hazcard and CLEAPSS Recipe Book.

Potassium bromide solution, KBr(aq) - see CLEAPSS Hazcard.  

Potassium iodide, KI(aq) - see CLEAPSS Hazcard and CLEAPSS Recipe Book. 

Silver nitrate solution, AgNO3(aq) - see CLEAPSS Hazcard and CLEAPSS Recipe Book.  Note that even this dilute solution can stain fingers and clothing.

1 It may be useful to colour code the pipettes containing the solutions, to prevent confusion.

2 All the solutions must be made up using deionised or distilled water. This is to prevent any unwanted cloudiness appearing on mixing with silver nitrate because of the presence of chloride ions in tap water.

Procedure

a Cover the worksheet containing the table with the plastic sheet.

b Put one drop of each of the halide ion solutions in the appropriate boxes.

c Add one drop of silver nitrate solution to the drop of halide solution in each of the boxes in the first column.

d Repeat the process for the second column using lithium bromide solution.

e Repeat the process for the third column using calcium nitrate solution.

f Record all your observations when the solutions are mixed.

Teaching notes

The first column compares the solubilities of silver halides. Silver fluoride is soluble, so no precipitate forms. The other silver halides are all insoluble and form as precipitates. The reactions can be represented by the ionic equation:

Ag+(aq) + X-(aq) → AgX(s), where X = Cl, Br and I.

It may be possible to distinguish the silver halides by colour: silver chloride is white (but darkens rapidly in strong light), silver bromide is off-white or cream, and silver iodide is pale yellow.

For the lithium halides in the second column, only lithium fluoride is insoluble, but a precipitate does not always form at these concentrations.

For the calcium halides, only the fluoride is insoluble, forming a white precipitate.

These experiments show that fluorides behave differently from the rest of the halides in each series. In Groups 1 and 2, the behaviour of the fluorides is not typical of the rest of the halides. This is because all the other halides of the metals in these groups are soluble.

At a suitable level, these trends can be discussed with students in terms of ion size, lattice energy and hydration energies of the aqueous ions. The small size of the fluoride ion is the main reason for it behaving differently from the other halide ions here.

Health & Safety checked, September 2014

Credits

This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry

Page last updated October 2015