Science Fenns K-5Grades K to 5
A balance with a cup of water and a sugar packet on one side, and the same cup with sugar stirred in on the other, both level.

Science / All lessons / Matter and Particles

Solutions and Conservation

Before and after dissolving. Same mass.

Lesson 12 of 41

Try this first

Before we start

Today’s story

Solutions and Conservation

Stir sugar into water and it seems to vanish. Your eyes say it is gone. A balance says otherwise.

When a solid dissolves, its particles spread out between the water particles. They are too small to see. The mass stays the same before and after.

This idea is called conservation of matter. Let us test it with a scale.

See it

Five steps. Every time.

    Hands on

    Does the Mass Change?

    30 minutes · Do this with a grown-up nearby

    You need

    • Kitchen scale
    • Clear cup
    • Water
    • Sugar
    • Spoon
    • Paper towel
    • Pencil

    Do this

    1. Weigh the cup with water. Write the number.
    2. Weigh a spoon of sugar on a paper towel. Write the number.
    3. Add the two masses together for your prediction.
    4. Pour the sugar into the water and stir until it dissolves.
    5. Weigh the cup with the solution.
    6. Compare the numbers.
    Write or draw: A table with water mass, sugar mass, predicted total and measured total.

    Watch for: Are the numbers equal or close? What could make them differ a little?

    Safety: Do not taste the solution and wipe up spills.

    Same every time

    Three rules

    Rule 1Matter is conserved

    It can change places, but it is not lost.

    Rule 2Weigh the whole thing

    Include the cup and every bit.

    Rule 3Check your error

    Small gaps come from measuring.

    Grandpa Fenn’s notebook

    Say it like a scientist

    solution
    A mix in which one substance is evenly spread through another.
    conservation of matter
    Matter is not made or destroyed in these changes.
    dissolve
    To spread out in a liquid until it cannot be seen.
    particle
    A bit of sugar or salt so small you cannot see it alone.

    Poppy’s quiz

    Six questions

    Tap an answer. Green means right. You will see why.

    Talk about it

    Say it out loud

    • How do you know matter was not lost?
    • When have you stirred something into a drink at home and watched it seem to vanish?
    Did you know

    If you let the water evaporate from a salt solution, the salt appears again.

    Someone who does this

    A pharmacist mixes exact amounts of medicine into liquids and relies on mass staying the same.

    BeforeMixtures Keep Their PartsNext lessonMatter Is Made of Particles