A substance's empirical formula shows the simplest whole number ratio of atoms of each element in a compound.

The relative formula mass of a substance is the sum of the relative atomic masses of all the atoms in a formula.

A substance's molecular formula shows the actual number of atoms of each element in a molecule of a compound.

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.

Empirical formula calculations: using moles

Combined science

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.

Calculations involving masses

The formula that shows the total number of atoms in a molecule.

The simplest whole number ratio of atoms of each element in a compound.

The formula that describes the types of chemical bonds in a compound.

The formula used exclusively in organic chemistry.

Which of the following best describes the term 'empirical formula'?

Write the empirical formula and molecular formula for a compound with a molecular formula of C₆H₁₂O₆.

The empirical formula of a compound is NH₃ and its relative formula mass (Mr) is 34. What is its molecular formula?

True or false? Empirical formula shows the simplest ratio of how many atoms there are of each element in a substance; molecular formula shows the exact numbers of atoms of each element.

Given the following information, calculate the empirical formula of a compound: 2.4 moles of magnesium and 4.8 moles of oxygen.

Given 40 g of carbon reacts with 10 g of hydrogen to form a compound, calculate the empirical formula of the compound. Use the relative atomic masses (Ar): Carbon = 12, Hydrogen = 1.

How many particles are in one mole of any substance?

Calculate the relative formula mass (Mr) of carbon dioxide (CO₂).

If 2 moles of hydrogen gas react with 1 mole of oxygen gas, how many moles of water are produced?

What is the mass (g) of 2 moles of carbon dioxide (CO₂)? 

If a compound is made of 30 g of carbon and 70 g of oxygen, what is the percentage by mass of carbon?

Starter Quiz