Empirical and Molecular Formulae

Lab Brief #8

🎯 Your mission

Run the experiment. Find out what really happens.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

The empirical formula gives the simplest whole-number ratio of atoms; the molecular formula gives the actual numbers. Both hydrogen peroxide, H₂O₂, and water contain only hydrogen and oxygen, but their formulae and behaviour differ completely.

Key words

empirical formula
The simplest whole-number ratio of atoms in a compound.
molecular formula
The actual number of each type of atom in one molecule.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

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

Get ready

🧰 What you need

magnesium ribbon
crucible with lid
pipeclay triangle
Bunsen burner
balance
tongs

Get ready

⚠️ Safety first

Burning magnesium is blindingly bright — never look directly at it.
Lift the lid only briefly with tongs; the crucible remains dangerously hot for several minutes.

Step 1 of 4 · Read

Think about what you just learned: say what "empirical formula" and "molecular formula" mean in your own words before you start.

Step 2 of 4 · Do

Heat weighed magnesium ribbon in a crucible until fully oxidised, reweighing to constant mass. Use the mass of magnesium and the mass of oxygen gained to derive the empirical formula of magnesium oxide.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

The empirical formula of C₆H₁₂O₆ is:

How sure are you?😐 maybe

Question 2 of 2

An empirical formula shows the:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 2 right.

All lessons

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✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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Empirical and Molecular Formulae

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