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Mole Mountain

The mole and Avogadro constant, how to switch between mass and moles using moles = mass divided by Mr, and how to use the ratio in a balanced equation to work out reacting masses.

⏱️ 18 min 🎯 14 activities
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What you'll cover

Counting the uncountable

Atoms are far too small and too many to count one by one, so chemists count them in a huge fixed group called the mole. Working with moles lets you turn a mass you can weigh into a number of particles, and lets you predict exactly how much of one substance reacts with another. This module builds the core mole calculations step by step.

Mole words to know

Learn these before you start the calculations.

Mass against moles

You switch between the two using the Mr.

Follow the fixed sequence

Reacting-mass questions always follow one order. Balance the equation first, then work out the moles of the substance you know, then use the ratio in the equation to find the moles of the substance you want, then turn those moles back into a mass. Show every line with its units, because that is where the marks are.

Match the term

  • the mole
  • the Avogadro constant
  • the Mr
  • the equation ratio
  • a fixed amount of substance
  • the particles in one mole
  • the mass of one mole in grams
  • how much reacts with how much

Match the calculation

  • to find moles
  • to find mass
  • to find the particles
  • to find reacting amounts
  • divide the mass by the Mr
  • multiply the moles by the Mr
  • multiply the moles by 6.02 x 10^23
  • use the ratio in the balanced equation

What is a mole?

What does one mole of a substance contain?

  • About 6.02 x 10^23 particles.
  • Exactly one hundred particles.
  • A single particle.
  • Always exactly one gram.

True about the mole

Select the TWO true statements.

  • Moles are found by dividing the mass by the Mr
  • The mass of one mole in grams equals the Mr
  • Every substance has the same mass per mole
  • A mole is a very small number of particles

Work out the moles

A sample has a mass of 48 g and its Mr is 12. Divide the mass by the Mr to find the number of moles. What is the answer?

Order the reacting-mass steps

Put the steps of a reacting-mass calculation in order, earliest first.

  • Balance the equation
  • Find the moles of the known substance
  • Apply the equation ratio
  • Convert the moles into a mass

Complete the rules

To find the number of moles, _____ the mass by the Mr. To go the other way and find a mass, _____ the moles by the Mr. One mole always contains about 6.02 x 10^23 _____. To find how much reacts, use the _____ in the balanced equation.

divide multiply particles ratio add subtract grams colour

Spot what you need

To work out the number of moles in a sample, tap the TWO things you must know.

  • the mass of the sample
  • the Mr of the substance
  • the colour of the sample
  • the temperature of the room

Pick the operation

Read each task and choose the correct step.

  • You have weighed 24 g of a substance and know its Mr. How do you find the moles?
  • You know you need 3 moles of a substance with an Mr of 40. How do you find the mass?
  • You want to know how much product forms from a known mass of reactant. What must you use?

Explain the mole method

Explain what a mole is and how to use moles to work out the mass of product from a known mass of reactant.

  • Say what a mole is and what the Avogadro constant counts
  • Explain how to change a mass into moles and moles back into a mass
  • Describe the order of steps for a reacting-mass calculation