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Science Launch G5 / Week 03 / Wednesday
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Week 03 · Mystery Materials

Wednesday

Investigation: The dissolving test
// Identify materials by their properties
⏱ about 15 min

Wednesday: Investigation: The dissolving test

Raven lines up two clear cups on a tray and labels them with tape: salt and sugar.

"Same amount of powder, same amount of water," she says. "That keeps it fair."

Rocket picks up a third cup marked with a question mark. "And this is our mystery," he says.

Nova scans the cups. "Every substance has its own solubility," she says. "Watch which one dissolves completely, and how fast."

Rocket rolls up his sleeves. "Let's see what happens!"

What you need

  • Three clear plastic cups and a marker or tape for labels
  • Room temperature water and a measuring spoon
  • Salt and sugar
  • Three spoons for stirring
Safety first
A grown-up prepares the mystery cup with salt or sugar and keeps it secret.
Nothing is tasted, not even a lick.
Wipe spills right away and wash your hands when you finish.

Steps

  1. Put 2 tablespoons of room temperature water in each cup.
  2. Add 1 tablespoon of salt to the salt cup.
  3. Add 1 tablespoon of sugar to the sugar cup.
  4. The grown-up adds 1 tablespoon of the secret powder to the mystery cup.
  5. Stir each cup the same number of times, about 20 stirs.
  6. Look closely at the bottom of each cup.
MAKE A PREDICTION
  • Read the question.
  • Tap your answer.
In this fair test, which do you predict will dissolve completely?
CupDissolved completely, or some left on the bottom?
Salt
Sugar
Mystery

In tests like this, sugar dissolves completely and fast. Salt dissolves more slowly, and some stays on the bottom.

Match the mystery cup to the cup that looks the same. That is your identification.

If the mystery cup has grains left on the bottom, which powder is it? Type salt or sugar.
WHY THIS EXERCISESalt and sugar have different solubility, so how they dissolve is a property that identifies them.
For a grown-up
After the test, reveal what you put in the mystery cup.
Pour the cups down the sink and rinse them.

A fair dissolving test

Same water, same amount of powder, same number of stirs.

Only the powder changed. That is what makes the test fair.

Because the test was fair, any difference comes from the powders themselves.

FAIR TEST CHECK
  • Read the question.
  • Tap your answer.
Why did every cup get 2 tablespoons of water?
In this test, which powder dissolved completely?
StatementTrue or false?
Every substance has its own solubility.?
Salt dissolved faster than sugar in this test.?
Stirring each cup the same number of times keeps the test fair.?
WHY THIS EXERCISEDifferent solubility let you tell salt from sugar.

You identified a mystery substance using evidence, not guessing. Tomorrow we will test hardness and shine.

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