Variation exists within a species

• factors that affect the rate (time taken) of dissolving:
  • temperature of the mixture
  • stirring or shaking the mixture
  • grain size of the solute

• Greet the learners.
• Ask them if they can remember what was discussed in the last lesson or lessons.
• Do a brief overview of the previous lessons on “Solutions and special mixtures. Ask your learners the following questions:
• When is a mixture also a solution?

Answer: When one substance dissolves into the other.

• What is the substance that we can see called?

Answer: Solvent.

• What substance has dissolved?

Answer: Solute.

• Give an example of a soluble solute (solids).

Answers could include: Sugar (solute) can dissolve in water (solvent). 

• What is a saturated solution?

Answer: When no more solute can dissolve in a solution – e.g. too much sugar in my tea.

• Give examples of insoluble substances?

Answers could include:  Water and oil, oil-based paint and water, sand and water, curry powder and water.

• Tell learners that they are going to learn about dissolving today.
• Tell learners that they are going to learn about the difference between dissolving and melting.
• Tell learners that they are first going to look at a video clip to remind them how a solid, a liquid and a gas differ from each other. They are going to see how the states change, which means, when a substance changes from one state (e.g. solid) to another (e.g. liquid).
• Show VIDEO CLIP 1: States of matter: Solids, Liquids and Gases: funza Academy Science Videos for kids (3:00 min.).

• Ask learners to complete WORKSHEET A: Substances dissolved to make coffee.
• Guide learners as they complete this activity and explain to them how their work will be assessed.

• Teacher to use WORKSHEET A: Memorandum to mark the learners’ work.

• Divide learners into groups.
• Tell learners that they will be designing and producing a science poster in their groups.
• Allow learners to choose which of the two posters below they want to produce:
• Poster 1: illustration of states of matter (solids, liquids and gasses).

     Learners can use video clip 1 for inspiration

• Poster 2: illustration of solutions as special mixtures showing:
  • Solute
  • Solvent
  • Soluble substances
  • Insoluble substances
  • Saturated solutions
• Inform learners that the posters are going to be placed on the classroom wall to help them remember the key facts about states of matter and solutions.
• Supply learners with materials that they will need to make their posters.

A3 or bigger sheets of paper; crayons, Koki’s or coloured chalk; old magazines (learners can use pictures for their posters); glue; scissors; etc.

• Guide learners as they complete this activity and explain to them how their posters will be assessed.

• Show VIDEO CLIP 2: Melting vs Dissolving – Watt’s Up? 5th grade collaboration Ep. 2 (5.07 min.).
• Present an overview of the difference between melting and dissolving by using PRESENTATION 1: The difference between melting and dissolving.

• Learners complete WORKSHEET B: Changing states of matter.
• Guide learners as they complete this activity and explain to them how this worksheet will be assessed.
• Teacher to use WORKSHEET B: Memorandum to mark the learners’ work.

• Learners complete the word search in WORKSHEET C: Word search.
• Guide learners in undertaking this activity and explain how this worksheet will be assessed.
• Teacher to use WORKSHEET C: Memorandum to mark the learners’ work.

• Ask learners if they can explain what is meant by “rate of dissolving.”
• Answer: It means how quickly a solute dissolves in a solvent.
• Ask the learners to think about a cup of coffee. Ask the learners why they stir their coffee after adding sugar to it.

Answer:  So that the sugar dissolves quicker.

• Ask learners: If stirring increases the rate of dissolving (helps the sugar to dissolve quicker), can they think of any other things that could increase the rate of dissolving?
• Answers can include: The rate at which the sugar dissolves into the cup of coffee will depend on:
  • how hot the cup of coffee is (temperature);
  • the speed at which the sugar is stirred into the coffee (fast or slow);
  • how the sugar has been processed – fine powder; sugar grains; sugar cubes (grain size of solute).

• Show VIDEO CLIP 3: Factors affecting the rate of dissolving (5.55 min.).

• Tell the learners that they are going to do a few experiments to find out how they can increase the rate at which a solute dissolves in a solvent.
• The following must be prepared for the experiments in WORKSHEET D, E and F: Investigations into factors that affect the rate of dissolving
• beakers
• coarse table salt
• fine table salt
• hot water (not boiling)
• room temperature water
• cold water (from a fridge)
• tablespoon
• stopwatch (cell phone)

• Divide learners into groups of 3 – 4.
• Allocate each group an investigation:
  • WORKSHEET D: Investigation – Does temperature affect the rate of dissolving?
  • WORKSHEET E: Investigation – Does stirring or shaking a mixture affect the rate of dissolving?
  • WORKSHEET F: Investigation – Does coarse salt dissolve faster or slower than fine salt?
• Explain how the investigations should be done and how the completed worksheets will be assessed.
• Teacher to use the memorandum provided for WORKSHEET D, E and F: to mark the learners’ work.
• BEFORE learners begin drawing their graphs provide an overview of graphs using PRESENTATION 2.

• Present an overview of the purpose and making of graphs by using PRESENTATION 2: Making and using graphs.
• Once learners understand the basic concepts of graphs, use PRESENTATION 3: Drawing a graph to explain how to draw the line graph required in Worksheet D, question 5.
• Explain how to draw the bar graphs required in WORKSHEET E AND F.
• After learners have completed their investigation, recorded their results and drawn their graphs, ask them what they have discovered so far about things that increase the rate of dissolving.

Answer: Three factors affect the rate of dissolving:

1. The temperature of the mixture.
2. The stirring or shaking of the mixture.
3. The grain size of the solute.

• Present a summary of the factors that affect the rate of dissolving by using PRESENTATION 4:

• Allow learners time to complete WORKSHEET G: Crossword puzzle to consolidate their knowledge about drawing graphs.
• Learners complete the crossword puzzle in WORKSHEET G: Crossword puzzle.
• Guide learners in undertaking this activity and explain how this worksheet will be assessed.
• Teacher to use WORKSHEET G: Memorandum to mark the learners’ work.