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Student Activity: Solutions (LA0019)

Author:  Rick Boyle
Published:  17th September 2002
Lesson plan:  LP0019
Introduction
Many solid substances dissolve when they are added to water. When this happens a solution is formed. Solutions have many important uses in chemistry.
Forming solutions (LF0019a)
Open the Crocodile Chemistry simulation file LF0019a.

When we make solutions with water, we use the word solvent to describe the water and the word solute to describe the substance that is being dissolved into it. When we make a solution we sometimes see surprising changes in colour.

  1. Add salt (sodium chloride) to water. Is the salt the solvent or the solute?
  2. Does the solution change colour?
  3. What colour is the copper chloride powder?
  4. Now add the copper chloride powder to water. What happens to the water?
  5. Is copper chloride the solvent or the solute?
When a substance is disolved in water, the water is known as the solvent. The substance that is dissolved is called the solute. When solutions are formed we sometimes get changes in colour.
Solutions, solubility and saturation (LF0019b)
Open the Crocodile Chemistry simulation file LF0019b.

A substance's ability to dissolve is known as its solubility. Some substances are better at dissolving in water than others because they have a higher solubility. When we dissolve a substance in water there is a limit that the water can hold in solution. When this limit is reached the solution is saturated. If any more of a substance is added to a saturated solution it stays as a solid and doesn't dissolve.

The solubility of a substance is usually given in g/100cm3. At room temperature (25 oC) salt has a solubility of 36g/100cm3 - this means that 36 grams of sodium chloride will dissolve in 100cm3 of water.

  1. Add 10 grams copper chloride powder to 100 cm3 of water. Pick the beaker filled with the solution and rotate it. Is there a solid at the bottom of the beaker?
  2. Can you name this solid?
  3. Is the copper chloride solution saturated?
  4. Now add salt to 100 cm3 of water. There are four portions each weighing 10 grams. Add them one at a time and watch what happens.
  5. How many portions are needed to saturate the water and turn it cloudy?
  6. Is salt more or less soluble than copper chloride?
  7. How many grams of salt could be dissolved in 200 cm3 of water?
A substance's ability to dissolve is known as its solubility. The solubility of a substance is usually given in g/100cm3. When no more solid can be dissolved the solution is saturated
Extension activity
  1. Use the chemistry simulator to make up cobalt chloride solution. Observe the changes in colour.
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