Moles, Mass and Formula Mass

Lab Brief #3

🎯 Your mission

Understand the idea. Then look for it everywhere.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

Moles equals mass divided by relative formula mass, n = m/Mr. Rearranged, it converts between what you can weigh and what actually reacts. Most quantitative chemistry problems are this triangle applied twice with a balanced equation in between.

Key words

amount of substance
The number of moles, calculated as mass divided by relative formula mass.
molar mass
The mass of one mole of a substance, in grams per mole.

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.

Step 1 of 4 · Read

Think about what you just learned: say what "amount of substance" and "molar mass" mean in your own words before you start.

Step 2 of 4 · Do

Work ten conversions both ways: find moles from a given mass, and mass from a given number of moles, for five different compounds. Include one where the answer must be given in kilograms.

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

How many moles are in 50 g of CaCO₃ (Mr = 100)?

How sure are you?😐 maybe

Question 2 of 2

The relationship between moles, mass and Mr is:

How sure are you?😐 maybe

Mind = blown

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

Nice work!

You got 0 of 2 right.

Next: Balancing Chemical Equations 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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