40-minute lesson
Grade 2 Science: Mixing materials
Lesson objective
- Mix everyday materials and describe what happens.
- Notice that some materials dissolve in water and some do not.
- Separate a simple mixture.
Success criteria:
- I can predict what will happen when I mix two materials.
- I can say whether a material dissolved in water.
- I can separate sand from water using a strainer and paper towel.
Materials
- Four clear plastic cups
- Water
- Teaspoons of salt, sand, sugar and cooking oil
- A spoon for stirring
- A tea strainer lined with a paper towel
Introduction
4 minIntroduce today's words:
- mix: To put two or more things together.
- mixture: Two or more materials put together.
- dissolve: When a solid seems to disappear into a liquid, like sugar in water.
- separate: To take parts of a mixture apart again.
Ask your child what they already know about mixing materials.
Explanation
8 minWhen we put two or more materials together, we make a mixture. Fruit salad, trail mix and muddy water are all mixtures.
Some solids dissolve in water. When you stir salt or sugar into water, the grains seem to disappear. They are still there, though: the water tastes salty or sweet.
Some solids do not dissolve. Sand sinks to the bottom of the cup and you can still see it.
Some liquids do not mix with water. Cooking oil floats on top of water in a layer.
We can separate some mixtures. Pouring sandy water through a strainer lined with paper towel catches the sand and lets the water through.
Cooks, builders and farmers mix materials every day. Concrete is a mixture of cement, sand, gravel and water.
Worked examples
6 minSalt in water
What happens when you stir a teaspoon of salt into a cup of water?
Step 1: Predict: will the salt disappear or stay at the bottom?
Step 2: Add the salt and stir for one minute.
Step 3: Look: the water looks clear again.
Step 4: The salt has dissolved, but it is still in the water.
Answer: The salt dissolves into the water.
Separating sand
How can you get the sand back out of sandy water?
Step 1: Line a strainer with paper towel and hold it over an empty cup.
Step 2: Slowly pour the sandy water in.
Step 3: Watch the water drip through.
Step 4: The sand stays on the paper towel.
Answer: Pour it through paper towel; the sand is caught and the water runs through.
Guided practice (do together)
8 min1. Which material dissolves in water?
(a) Sand (b) Sugar (c) Pebbles (d) Cooking oil
2. What happens when you pour cooking oil into water?
(a) It dissolves (b) It turns to sand (c) It floats on top (d) It disappears
3. Which of these is a mixture?
(a) Fruit salad (b) A single grape (c) One grain of salt (d) A single pebble
4. How can you separate sand from water?
(a) Stir it faster (b) Add more sand (c) Put it in the fridge (d) Pour it through paper towel
Independent practice
10 min5. After salt dissolves, how could you tell it is still in the water (with an adult's OK)?
(a) The water is hot (b) The water tastes salty (c) The water turns blue (d) The water is gone
6. When sugar seems to disappear in water, we say it d________.
7. Does sand dissolve in water? Answer yes or no.
8. Two or more materials put together make a m______.
Questions to check understanding
- Can you predict what will happen when I mix two materials?
- Can you say whether a material dissolved in water?
- Can you separate sand from water using a strainer and paper towel?
- What was the trickiest part today?
Answer guide
1. Sugar — Sugar dissolves when stirred into water.
2. It floats on top — Oil does not mix with water; it floats as a layer on top.
3. Fruit salad — Fruit salad is many foods put together, so it is a mixture.
4. Pour it through paper towel — The paper towel catches the sand and lets water through.
5. The water tastes salty — The salt is still there, so a tiny taste is salty.
6. dissolves — Sugar dissolves in water.
7. no — Sand does not dissolve; it sinks to the bottom.
8. mixture — Materials put together make a mixture.
Review
4 minRecap the success criteria together. Watch for these common misconceptions:
- Children often think dissolved salt or sugar has gone. It is still there, in pieces too small to see.
- Some think 'melting' and 'dissolving' are the same. Melting needs heat (ice to water); dissolving is mixing into a liquid.
- Some think all liquids mix with water. Oil does not.
Extension activities
- Try dissolving sugar in warm water and cold water (adult pours the warm water). Which dissolves faster?
- Leave a saucer of salty water in a sunny spot for a few days and look for salt crystals.
- Make a muddy-water filter using a cut plastic bottle, cotton wool, sand and gravel.
Suggested follow-up
- Revisit mixing materials tomorrow with two or three quick questions from memory.
- Try the online practice check for this topic and look at any questions that need another go.
Tips for parents
- Label each cup before mixing so results are easy to compare.
- Only allow tasting of food-safe mixtures (salt water or sugar water) and only with your permission.
- Safety: wipe up spills straight away so floors are not slippery, and never mix cleaning products.