Grade 11 · 🧪 Chemistry · Stoichiometry · CHE-G11-S1.1
Feel how big Avogadro's number really is — using rice
Weigh 100 grains of rice, then calculate how much a mole of rice would weigh. The answer shows just how tiny atoms are.
Why this matters
Pharmacists dose paracetamol by mass, but what matters inside your body is the number of molecules: 500 mg is about 2 × 10²¹ of them. The mole is the bridge between the grams you can weigh and the atoms you can't see.
Watch the demo
Video by TED-Ed
The science
What is a mole?
1 mole = 6.022 × 10²³ particles (Avogadro's number N_A). It's just a counting unit — like 'dozen' = 12, but vastly bigger because atoms are vastly smaller than eggs.
Molar mass
The molar mass of a substance (g/mol) is the sum of atomic masses on the periodic table. Water H₂O: 2·(1) + 16 = 18 g/mol. So 1 mole of water weighs 18 g.
Converting mass ↔ moles ↔ particles
Moles = mass / molar mass. Particles = moles × N_A.
You'll need
- A handful of uncooked rice↳ Teff grains also work, but are much harder to count
- A kitchen scale↳ No scale? A level teaspoon of rice is about 5 g
- Paper, pen and a calculator
Safety first
- No special safety needed.
Step by step
0/4 doneWhat you should see
One grain weighs about 25 mg. A mole of rice comes out at about 1.5 × 10¹⁹ kg — far more rice than has ever been grown on Earth.
Why it happens
A mole of water molecules fits in a single 18 g spoonful, but a mole of rice grains would be a mountain range. The same count gives wildly different masses because atoms and molecules are unimaginably smaller than rice grains.
Didn't work? Try this
My scale shows 0 g for 100 grains.
Kitchen scales often can't weigh less than a few grams. Weigh 500 grains instead and divide by 500.
My calculator shows an error.
Type 6.022 × 10²³ using the EXP or ×10ˣ key: 6.022 EXP 23.
Still stuck? Ask the lab assistant
Check your understanding
1. What does Avogadro's number represent?
2. How many moles are in 9 g of water (18 g/mol)?
Your lab notebook
Loading…