Science Fenns K-5Grades K to 5
A kitchen scale with a sealed jar of water and a spoonful of salt beside it, with a notebook showing two weights.

Science / All lessons / Matter and Mixtures

Matter Is Conserved

Weigh before. Weigh after. Same total.

Lesson 12 of 40

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Before we start

Today’s story

Matter Is Conserved

Tess pours soil into a jar of water. She weighs the jar before and after she shakes it. The water turns brown. The jar looks different. The number on the scale is exactly the same.

Matter can mix, spread out, settle and change shape. The total amount stays the same. This idea is called conservation of matter. If you put it in, it is still there. If you weigh all the parts before and after, the total matches.

The scale proves it. It is easy to get fooled by what the eye sees. A mixture may look like less or more. The balance tells the truth. Here are the steps.

See it

Five steps. Every time.

    Hands on

    Weigh the Mix

    25 minutes · Do this with a grown-up nearby

    You need

    • A kitchen scale or balance
    • A jar with a lid
    • Water
    • Soil
    • Oil
    • A spoon
    • Paper towels
    • Notebook

    Do this

    1. Weigh the empty jar and write the mass.
    2. Add water and weigh again.
    3. Add the soil and weigh the jar again before shaking.
    4. Close the lid and shake for ten seconds.
    5. Weigh again.
    6. Repeat with oil and water in a fresh jar.
    7. Compare the before and after numbers.
    Write or draw: A table with Mixture, Mass before, Mass after and Difference.

    Watch for: Notice that the total did not change. Small differences might be from spilled drops or from scale error.

    Safety: Close lids tight and wipe up spills right away.

    Same every time

    Three rules

    Rule 1Weigh before and after.

    Numbers beat guesses.

    Rule 2Keep it all inside.

    Spills give a wrong answer.

    Rule 3Use the same scale.

    Different scales can differ a little.

    Grandpa Fenn’s notebook

    Say it like a scientist

    conserved
    Kept the same. Not lost and not gained.
    mass
    How much matter an object has.
    total
    All the parts added together.
    balance
    A tool that measures mass.

    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 no matter was lost when you mixed?
    • When you pour milk on cereal at home, how could you show the total stays the same?
    Did you know

    In the 1700s a French chemist named Antoine Lavoisier weighed everything before and after a change. He kept getting the same total.

    Someone who does this

    A lab chemist weighs materials before and after mixing to be sure nothing is lost.

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