Introduction
- factors that affect the rate (time taken) of dissolving:
- temperature of the mixture
- stirring or shaking the mixture
- grain size of the solute
Teacher Input 1
- 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.).
Learner Activity 1
- 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.
Learner Activity 2
- 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.
Teacher Input 2
- 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.
Learner Activity 3
- 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.
Learner Activity 4
- 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.
Teacher Input 3
- 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).
Teacher Input 4
- 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)
Learner Activity 5
- 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.
Teacher Input 5
- 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:
- The temperature of the mixture.
- The stirring or shaking of the mixture.
- The grain size of the solute.
- Present a summary of the factors that affect the rate of dissolving by using PRESENTATION 4:
Learner Activity 6
- 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.
Revision Activity 1
- Learners complete QUIZ 1
- Teacher to support learners as they undertake this quiz.
- Teacher to explain how this quiz will be assessed.
- Teacher to use QUIZ 1: Memorandum to mark the learners’ work.
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