2. Explain how a solution is made

Prior Learning: 

Revise learning from upper KS2 by recapping on solutes, solvents and solutions. Discuss the homework assignment from lesson 1 - what elements and compounds did the students research?

Starter

Begin by asking the students: what happens to a sugar cube when it is added to a cup of coffee or tea? Write the definition of a solution on the board: "A solution is a homogeneous mixture of two or more substances." Introduce the concept of solute and solvent, defining them as:

• Solute: The substance that is dissolved in a solution.
• Solvent: The substance that dissolves the solute, making up the majority of the solution.

Introduce the concept of solubility, defining it as "the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature." Introduce the concept of saturation, defining it as "the point at which a solution can no longer dissolve any more solute."

Main Teaching

Direct Instruction:

• Distribute handouts with definitions and examples of solutions.
• Review the definition of a solution and the components of a solution (solvent and solute).
• Use the salt and water example to demonstrate how a solute (salt) is dissolved in a solvent (water) to form a solution. Show the solubility of salt in water at room temperature.
• Have students work in pairs to create a list of other examples of solutions, identifying the solute and solvent in each example.

Guided Practice:

• Have students form small groups and provide them with different solutes and a large container of water.
• Ask them to determine the solubility of each solute in water by adding a small amount at a time, stirring and observing if the solute dissolves or not.
• Have each group present their findings and explain the concept of solubility and saturation in their examples.

Independent Practice:

• Have students complete a worksheet that asks them to identify the solute and solvent in given solutions, explain how it is a solution and write down the solubility and saturation point of the solute in the solvent.

Career Film: Carrington Watkins is a Project Management Development Programme with Rolls Royce. "The career opportunities here changed everything."

Expert Film: Dr Sam Rowe as he demonstrates what happens when salt, sand and copper sulphate are added to water.

Mission Assignment

Saturation Investigation

Students should fill three beakers with 150 ml of water. One beaker should have cold water in it, one should have room temperature water, and the third should have hot water in it. 

To investigate the saturation point of each beaker of water, students should add a level spatula of solute, such as salt or sugar, to each beaker of water to make a solution. Solute should keep being added until the saturation point is reached i.e. when it remains visible in the solution. 

Each time a spatula of solute is added, students should make a note in the handout and the solution should be stirred until the solute dissolves. 

Once a beaker has reached its saturation point, no more solute should be added to it, but more should be added to the ones whose saturation point has not been reached yet. They should continue until all three beakers are saturated. 

Students should find that the coldest beaker has the lowest saturation point and the warmest beaker has the highest saturation point.

Differentiated tasks (Support/Core/Challenge)

Support: Use simple diagrams to help explain the concepts.

Core: Provide more detailed explanations and examples to help with understanding.

Challenge: Introduce advanced concepts such as solubility curves, and real-world applications of solutions. For these students the following experiment can be conducted:

• Provide the group with a beaker of water, a graduated cylinder, a thermometer, a test tube, and a small amount of sugar and salt.
• Instruct the students to measure 50ml of water in the graduated cylinder and pour it into the beaker.
• Ask them to measure the temperature of the water and record it.
• Then, ask them to add a small amount of sugar or salt to the water and stir it.
• Ask students to measure the temperature and record it.
• Ask students to observe the amount of solute that dissolved in the water and record it.
• Repeat the experiment with different temperatures and different solutes.