Chemistry Moles, Equations, and Calculations: GCSE Key Concepts

What is a mole?

The amount of substance containing 6.02 × 10²³ particles

What is Avogadro's constant?

6.02 × 10²³ particles per mole

What does 'particles' mean?

Atoms, molecules, or ions

Why are moles used in chemistry?

To compare amounts of substances fairly

Equation to calculate moles from mass?

Moles = mass ÷ Mr

Equation to calculate mass from moles?

Mass = moles × Mr

What does Mr stand for?

Relative formula mass

What does Ar stand for?

Relative atomic mass

What is the molar volume of a gas at RTP?

24 dm³ per mole

Equation for gas calculations?

Volume = moles × 24

Equation to find moles of gas?

Moles = volume ÷ 24

Unit used for gas volume at RTP?

dm³

Equation for concentration (GCSE)?

Concentration = moles ÷ volume

Units for concentration?

mol/dm³

Equation linking mass concentration?

Concentration (g/dm³) = mass ÷ volume

First step in reacting mass questions?

Write a balanced equation

Why is balancing important?

It shows the mole ratio

What does the mole ratio come from?

The numbers in the balanced equation

What is a limiting reactant?

The reactant that runs out first

Equation for percentage yield?

(Actual yield ÷ Theoretical yield) × 100

Why is yield often less than 100%?

Product lost, reversible reactions, or side reactions

Equation for percentage atom economy?

(Mr of desired product ÷ Mr of all products) × 100

Why is high atom economy important?

Less waste, more sustainable

What unit mistake loses marks in mole questions?

Not converting cm³ to dm³

How do you convert cm³ to dm³?

Divide by 1000

What's the MOST common mole equation error?

Forgetting to use Mr

What MUST you write to get method marks?

Equations and working