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.

Empirical formula calculations

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 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 120g of carbon reacts with 10g of hydrogen to form a compound, calculate the simplest ratio of carbon:hydrogen in the compound. Use the relative atomic masses (Ar): carbon = 12, hydrogen = 1.

A compound is 85.7% carbon and 14.3% hydrogen by mass. Calculate its empirical formula. Use the relative atomic masses (Ar): carbon = 12, hydrogen = 1.

Which of the following is the correct formula for carbon dioxide?

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

If two molecules of hydrogen gas react with one molecule of oxygen gas, how many molecules of water are produced?

A reaction requires three molecules of nitrogen gas and nine molecules of hydrogen gas. What is the simplest ratio of nitrogen to hydrogen needed for this reaction?

If one unit of carbon dioxide has a mass of 44 grams, what would be the mass of two units of carbon dioxide?

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

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Empirical formula calculations

Lesson outcome