C. Matter and Energy · Properties of Liquids and Solids

Mixing Liquids and Solids

C2.5 A1.2 A1.4 A2.1 A3.1About 40 minutes

Learning goals

I can describe what happens when I mix a solid with a liquid.
I can tell which solids dissolve in water and which do not.
I can tell which liquids mix and which do not.
I can name useful mixtures we make at home and in our community.
I can follow safety rules: only mix what a grown-up says is safe, and never mix cleaners.

Words to know

mixture
Two or more things mixed together, like trail mix or lemonade.

dissolve
When a solid mixes into a liquid so well that you cannot see it anymore, like sugar in water.

settle
To sink to the bottom and stay there, like sand in water.

stir
To move a spoon around and around to mix.

code
Steps written in order for a computer or robot to follow.

A drink on a hot day

You help make a jug of lemonade. You pour in water, add a scoop of lemonade powder and stir. The powder disappears! The water turns yellow and tastes sweet.

Where did the powder go? It is still there. It dissolved into the water. You just made a mixture!

A glass jug of yellow lemonade with lemon slices and a long spoon, next to a bowl of lemons on a picnic table. — When lemonade powder or sugar is stirred into water, it dissolves. You can't see it any more, but you can taste it. AI-generated image

What is a mixture?

A mixture is two or more things mixed together. We can mix:

a solid and a liquid (sugar and water, sand and water)
a liquid and a liquid (water and juice, oil and water)
a solid and a solid (trail mix, sand and pebbles)

Today we will focus on mixing liquids and solids.

Solid + liquid: Does it dissolve?

When you stir some solids into water, they dissolve. They break into pieces so tiny that you cannot see them. The water may look clear, but the solid is still there. (That is why sugar water tastes sweet.)

Other solids do not dissolve. You can still see them. They float, or they settle at the bottom.

Solid stirred into water	What happens?
sugar	dissolves (you can't see it)
salt	dissolves (you can't see it)
drink crystals	dissolve and colour the water
sand	does not dissolve; settles at the bottom
rice	does not dissolve; settles at the bottom
a pebble	does not dissolve; sinks

Some solids dissolve in water and some do not.

Liquid + liquid: Do they mix?

Water and juice mix together. You cannot see two separate liquids.
Oil and water do not mix. Even if you shake them, the oil soon floats back up and makes a layer on top. That is why you shake salad dressing before you pour it!

Warm water helps

Sugar dissolves faster in warm water than in cold water. Stirring helps it dissolve faster too.

Three mixtures. Sugar dissolves and seems to disappear, sand settles at the bottom, and oil floats in a layer on top of the water.

Useful mixtures

People mix liquids and solids to make many useful things:

Food: lemonade, hot chocolate (powder in warm milk), pancake batter, bread dough and bannock (a bread made by many First Nations and Métis families) all start by mixing dry ingredients like flour with liquids.
Crafts: flour and water make a sticky paste for papier-mâché. Paint is a mixture.
Building: concrete for sidewalks is made by mixing cement, sand, gravel and water. It is a thick liquid mixture at first, and then it hardens into a strong solid.
Cleaning: a few drops of dish soap in water make soapy water for washing dishes.

🍋🥞🍞🎨🧱

Useful mixtures: lemonade, pancake batter, bread dough, paint and concrete.

Mixing safety rules

Only mix things a grown-up says are safe, like water, sugar, salt, sand and food from the kitchen.
Never mix cleaning products. Some cleaners mixed together make dangerous gases. Even grown-ups should never mix them.
Never taste a science mixture unless a grown-up says it is only food.
Wipe up spills and wash your hands when you are done.

Worked example

Let's test: Which solids dissolve?

We stir a spoonful of sugar, salt, sand and rice into four clear cups of water. Which ones dissolve?

Make it fair: Use the same amount of water in each cup and one spoonful of each solid. Stir each cup 10 times.
Predict: I think sugar and salt will dissolve, because they disappear in cooking. I think sand and rice will not.
Observe: In the sugar and salt cups, the grains get smaller and disappear. The water looks clear again. In the sand and rice cups, the grains fall to the bottom and stay there.
Record: Make a chart: dissolved, or settled.

Sugar and salt dissolve in water. Sand and rice do not dissolve; they settle at the bottom.

Worked example

Let's make a useful mixture: flour paste for a craft

We want glue for a papier-mâché project. Can we make it by mixing a solid and a liquid?

Solid: Put about half a cup of flour in a bowl.
Liquid: Add water a little at a time.
Stir until it is smooth and thick, like white glue. If it is too runny, add more flour. If it is too thick, add more water.
Use it: Dip strips of newspaper in the paste and lay them over a balloon or a bowl. When it dries, it becomes hard.

Flour and water make a paste: a useful mixture of a solid and a liquid. It is sticky when wet and hard when dry.

Imagine this

A lemonade robot follows its code exactly. If you forget to write "Add lemonade powder", it will proudly serve you... a glass of plain water!

Code it: A robot that makes lemonade

A robot follows code: steps in the right order. Programmers break a big job into small steps. Here is code for a robot that makes a glass of lemonade from powder.

1. Get a cup.

2. Pour 250 mL of water into the cup.

3. Add 1 scoop of lemonade powder.

4. Stir 10 times.

5. Look: Can you still see powder?

6. If YES, stir 5 more times and go back to step 5.

7. If NO, the lemonade is ready!

Code for a lemonade robot. Steps 5 and 6 repeat until the powder has dissolved.

Hands-on activity

Mixing lab

You need: 6 clear plastic cups, water, a spoon, and small amounts of sugar, salt, sand (or soil), rice, cooking oil and juice. A grown-up helps.

Fill each cup halfway with water.
Make a chart with three columns: What I added, My prediction, What happened.
Add one spoonful of a different thing to each cup. Stir 10 times.
Watch for one minute. Did it dissolve? Settle at the bottom? Float on top? Mix in?
Record your results.
Bonus: Put a spoonful of sugar in a cup of warm tap water and another in cold water. Stir both the same number of times. Which dissolves faster?
Code it: Write the steps for a robot to do one of your tests. Read them to a grown-up who acts like the robot and does exactly what you say!

Safety: Use only the things on this list. Do not taste. Never mix cleaning products.

Your turn

What is a mixture?

Does sugar dissolve in water?

What happens to sand in water?

Do oil and water mix?

Name a useful mixture of a solid and a liquid.

Why should you never mix cleaning products?

Does sugar dissolve faster in warm water or cold water?

More practice: warm-up

Is trail mix a mixture?

Does salt dissolve in water?

Does a pebble dissolve in water?

What do you do with a spoon to help something dissolve?

Who decides if something is safe to mix?

More practice: on your own

After you stir sugar into water, you can't see it. How do you know it is still there?

Why do you shake a bottle of oil-and-vinegar salad dressing before pouring?

Name the solids and the liquid used to make concrete.

In the dissolving test, why did we stir every cup 10 times?

In the lemonade code, why does step 6 say "go back to step 5"?

Challenge

Find the bug! A robot's code says: 1. Stir 10 times. 2. Get a cup. 3. Add water. 4. Add powder. What is wrong? Fix it.

Sam mixed sand into water. Then he poured it through a paper coffee filter. What do you think happened?

Concrete starts as a thick wet mixture but ends up as a hard solid sidewalk. Why is that useful?

Check your understanding

Quiz

Which solid dissolves in water?

What happens when you pour oil into water?

Which is a useful mixture of a solid and a liquid?

Which is the safe choice?

Sugar dissolves faster in...

In code, why does the order of the steps matter?

For parents and teachers

Big idea: Liquids and solids can be combined into useful mixtures (C2.5). Some solids dissolve (sugar, salt), others settle (sand, rice). Some liquids mix (juice and water); others separate (oil and water). Many everyday products, from food to concrete, are mixtures.

Coding (A2.1): The lemonade robot breaks a task into small steps and repeats a step until a condition is met. Playing "robot" (you follow the code exactly as written) is a fun way to find bugs.

How to help: Cook together and name the mixtures. Ask, "Did it dissolve? Can you still see it?"

Common difficulties:

Thinking dissolved sugar has disappeared. It is still there; the water tastes sweet and the sugar can be left behind if the water dries up.
Confusing melting and dissolving. Melting needs heat and one substance changes state; dissolving is a solid mixing into a liquid.

Safety (A1.4): Only kitchen materials for this lesson. Explain clearly that some cleaners (for example, bleach and products containing ammonia) can make toxic gases when mixed. Children should never mix cleaners, and adults should not either.