The Law of Definite Proportions

Lab Brief #5

🎯 Your mission

Run the experiment. Find out what really happens.

⚡ The twist

If it bubbles, something invisible is escaping.

What you'll learn

The law of definite proportions states that a compound always contains the same elements in the same ratio by mass. Water is always 11.2% hydrogen and 88.8% oxygen.

Key words

conservation of mass
Matter is never made or destroyed, only changed in a reaction.

Make a hypothesis first

Guess: will the fizz be loud, soft, or none at all?

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

vinegar
baking soda

⚠️ Safety first

Wear eye protection, keep the substance off skin, and wash your hands when you finish.

Step 1 of 4 · Read

Look at the vocabulary words and write a definition for each in your own words.

Step 2 of 4 · Do

Mix baking soda and vinegar in a sealed bag. Weigh the bag before and after. Did the mass change? Explain why or why not using the law of conservation of mass.

Step 3 of 4 · Observe

Observe what happens and describe it in detail.

Step 4 of 4 · Record

Record your observations in your science journal with measurements and descriptions.

Question 1 of 3

Which state of matter has a definite shape and volume?

How sure are you?😐 maybe

Question 2 of 3

How is a compound different from a mixture?

How sure are you?😐 maybe

Question 3 of 3

What is mass?

How sure are you?😐 maybe

Mind = blown

💧 Hot water can freeze faster than cold water under the right conditions. Nobody fully understands why.

Nice work!

You got 0 of 3 right.

Next: Distillation All lessons

🎯

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✨ More to explore

🌍 Where you see this in real life: This is happening in your kitchen right now — every time food cooks.

🏆 Stretch challenge (try it this week): Find one ingredient in a snack and look up what it does.

👨‍👩‍👧 For the dinner table: “What's something we cook that mixes things together this way?”

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The Law of Definite Proportions

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