The effect of temperature on solubility

Most solid substances that are soluble in water are more soluble in hot water than in cold water. This experiment examines solubility at various temperatures.

This experiment should take 60 minutes.

Equipment 

Apparatus

• Eye protection
• Boiling tubes
• Beaker to act as ice bath, 250 cm³
• Beaker to act as a hot water bath, 250 cm³
• Stirring thermometer (-10 –110 °C) 
• Measuring cylinder or graduated pipette, 250 cm³
• Wooden tongs to hold hot boiling tube

Chemicals

• Ammonium chloride
• Ice

Health, safety and technical notes

• Read our standard health and safety guidance
• Wear eye protection.
• Ammonium chloride is harmful if swallowed and an eye irritant, see CLEAPSS Hazcard HC009a.

Procedure

1. Set up a hot water bath and an ice bath. Put 2.6 g of ammonium chloride into the boiling tube. Add 4 cm³ water.
2. Warm the boiling tube in the hot water bath until the solid dissolves.
3. Put the boiling tube in the ice bath and stir with the thermometer. Use wooden tongs to hold it if necessary.
4. Note the temperature at which crystals first appear and record it in the table
5. Add 1 cm³ water. Warm the solution again, stirring until all the crystals dissolve.
6. Then repeat the cooling and note the new temperature at which crystals appear.
7. Repeat steps 5, 6 and 7 until 10 cm³ water has been used.

Notes

This is a good opportunity to introduce the use of quantitative chemical apparatus to younger students.

Students should know that solids are generally more soluble in hot water than in cold water.

Questions

1. Plot a graph showing solubility on the vertical axis and temperature on the horizontal axis.