A mole of something is 6.02 × 10²³ of it. The mass of a mole of a substance is its relative mass expressed in grams.

Volume is how much 3D space matter occupies. It is usually measured in cm³.

Molar gas volume is the volume occupied by one mole of any gas. It is equal to 24 dm³ or 24 000 cm³ at room temperature and pressure.

Stoichiometry refers to the molar ratio of the reactants and products in a chemical reaction.

A balanced symbol equation describes a reaction using a symbol equation with coefficients, which ensure there are equal numbers of atoms of each element on both sides of the symbol equation.

Converting between mass and volume using moles

Chemistry

In the Making salts unit, pupils will learn about the production of pure salts, concentration and strength of acids, and what makes acids acidic and how bases can neutralise them.

In the Understanding Chemical Reactions unit, pupils learned about how atoms rearrange during chemical reactions and the conservation of mass.

This unit covers writing chemical formulae, balancing equations, and using the conservation of mass. It includes calculating moles, empirical formulae, relative formula masses, and theoretical yields. Emphasis is on stoichiometry, concentration, gas volumes, and using standard form.

Calculations involving masses

When converting the volume of a gas to the mass of a solid reactant in a balanced reaction, what must you first determine?

Calculate the number of moles of gas from its volume.

Use the stoichiometry of the balanced equation to find the moles of reactant.

Calculate the mass of the reactant using its relative mass.

Order the following steps to calculate the mass of a solid reactant from the volume of a gas product in a chemical reaction. Starting with the volume of gas.

If 24 dm³ of hydrogen gas react with oxygen to form water, how many moles of oxygen gas were used?
2H₂ + O₂ → 2H₂O.

A sample of oxygen gas weighing 16 grams is used in a reaction. Calculate the volume it occupies at room temperature and pressure.
The RFM of oxygen (O₂) is 32.
The molar gas volume is 24 dm³

Calculate the volume of CO₂ gas produced when 100 g of CaCO₃ decomposes.
CaCO₃ → CaO + CO₂.
Assume all the CaCO₃ reacts, the molar gas volume is 24 dm³.
RFM of CaCO₃ = 100, CaO = 56, CO₂ = 44.

Given 500 cm³ of oxygen gas at RTP, calculate the mass of H₂ gas that completely reacts with it to form water. Give answer to 2 s.f.
2H₂ + O₂ → 2H₂O.
The molar gas volume is 24 dm³.
RFM (Mr) of H₂ = 2

Which unit is most commonly used to measure the volume of a gas?

What is the molar gas volume of any gas at room temperature and pressure (20°C and 1 atmosphere)?

Molar gas volume is the volume occupied by {{}} of any gas at room temperature and pressure, standardised at 24 dm³ or 24 000 cm³.

Which equation would you use to calculate the number of moles from the volume of a gas?

True or false? The number of moles of a gas can only be calculated if you know the volume of the gas and the conditions of temperature and pressure.

Calculate the volume of 0.5 moles of nitrogen gas at room temperature and pressure. Assume the molar gas volume is 24 dm³ per mole. Give your answer to 2 s.f.
Volume of nitrogen gas = {{}} dm³.

Starter Quiz