Empirical formula calculations: using moles
Lesson details
Learning outcome
I can determine the empirical formulae of simple compounds using reactant masses or percentage composition.
Key learning points
- Empirical formula is the simplest whole number ratio of atoms of each element in a compound.
- Using the masses of elements reacted together, or their percentage compositions, calculate the empirical formula.
- Knowing the relative formula mass of a substance, and its empirical formula, calculate the molecular formula.
- Know that we are using moles, and molar ratios to calculate formulae
Keywords
Empirical formula - A substance's empirical formula shows the simplest whole number ratio of atoms of each element in a compound.
Relative formula mass - The relative formula mass of a substance is the sum of the relative atomic masses of all the atoms in a formula.
Molecular formula - A substance's molecular formula shows the actual number of atoms of each element in a molecule of a compound.
Mole - 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.
Common misconception
Pupils easily confuse empirical and molecular formula.
Provide multiple examples of formula and challenge pupils to distinguish them as molecular or empirical formula; if the former, push pupils to suggest the molecule's empirical formula.
Teacher tip
This topic is provides a useful link to organic chemistry and developing generic formula for different molecules of the same homologous series.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is the chemical formula for water?
Q2.How many particles are in one mole of any substance?
Q3.Calculate the relative formula mass (Mr) of carbon dioxide (CO₂).
Q4.If 2 moles of hydrogen gas react with 1 mole of oxygen gas, how many moles of water are produced?
Q5.What is the mass (g) of 2 moles of carbon dioxide (CO₂)?
Q6.If a compound is made of 30 g of carbon and 70 g of oxygen, what is the percentage by mass of carbon?
Assessment exit quiz
6 Questions
Q1.Which of the following best describes the term 'empirical formula'?
Q2.Write the empirical formula and molecular formula for a compound with a molecular formula of C₆H₁₂O₆.
Q3.The empirical formula of a compound is NH₃ and its relative formula mass (Mr) is 34. What is its molecular formula?
Q4.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.
Q5.Given the following information, calculate the empirical formula of a compound: 2.4 moles of magnesium and 4.8 moles of oxygen.
Q6.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.
To help you plan your 10 chemistry lesson on: Empirical formula calculations: using moles, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 chemistry lesson on: Empirical formula calculations: using moles, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 4 chemistry lessons from the Calculations involving masses unit, dive into the full secondary chemistry curriculum, or learn more about lesson planning.