Mass in a chemical reaction: using moles
Lesson details
Learning outcome
I can interpret a balanced symbol equation to predict the mass of either a reactant or a product.
Key learning points
- In a chemical reaction, the atoms in reactants are rearranged and are the same atoms that are in the products.
- Chemical equations are most correctly interpreted in terms of molar ratios (i.e. 1 mole of A reacts with 2 moles of B).
- The molar ratios of the substances in a chemical reaction is known as stoichiometry, which means ‘measuring elements’.
- The stoichiometry of a reaction is shown by coefficients in a balanced equation. These molar relationships don't change.
- The moles of substance in a reaction can be determined using: mass(g) = Mr × moles (& the stoichiometry of reaction).
Keywords
Stoichiometry - Stoichiometry refers to the molar ratio of the reactants and products in a chemical reaction.
Relative formula mass - The relative formula mass (RFM or Mᵣ) of a substance is the sum of the relative atomic masses of all the atoms in its formula.
Mole - 1 mole of a substance is 6.02 × 10²³ particles of it. The mass of a mole of a substance is its relative mass in grams.
Coefficient - A coefficient is the number placed in front of a chemical formula to balance an equation; it multiplies all the atoms in the formula and shows the ratio of substances in a reaction.
Balanced symbol equation - A balanced symbol equation represents a chemical reaction using symbols and coefficients to ensure that the number of atoms of each element is equal on both sides of the equation.
Common misconception
Pupils struggle to recall the order of steps required to mathematically process the available information in order to answer the question.
Colour-coding the steps can help pupils remember how many steps are involved. Much practice and perseverance is needed to create and maintain the memory pathway of the mathematical processing.
Teacher tip
Use of modelling via visualisers, colour-coding and faded 'I do, you do' examples is particularly useful to help pupils develop a memory strategy for the mathematical processing required to answer these types of questions. Much practice and perseverance is required to build confidence with this.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Given the relative atomic masses (Ar): C (12), O (16)
Calculate the relative molecular mass (Mr) of carbon dioxide (CO₂).
Q2.What does the conservation of mass in a chemical reaction imply?
Q3.If 20 g of sodium reacts fully with 15 g of chlorine, how much sodium chloride is produced?
Q4.For the equation __ N₂ + __ H₂ → __ NH₃, select the correct coefficients to balance it.
Q5.What does the equation 2H₂ + O₂ → 2H₂O tell us?
Q6.Given the relative atomic mass values (Ar): H (1), S (32), O (16)
Calculate the relative formula mass (Mr) of sulfuric acid.
Assessment exit quiz
6 Questions
Q1.What does stoichiometry mean in chemistry?
Q2.In a balanced chemical equation, what does the mole ratio of reactants and products tell us?
Q3.The is the sum of the relative atomic masses of all the atoms in a formula, representing the mass of a molecule relative to the mass of a carbon-12 atom.
Q4.Which of the following statements best describes what the equation 2H₂ + O₂ → 2H₂O tells us?
Q5.Given the reaction: CH₄ + 2O₂ → CO₂ + 2H₂O, how many grams of CO₂ are produced when 16 g of methane (CH₄) reacts completely? Relative formula mass values: (CH₄ = 16) & (CO₂ = 44)
Q6.Using the reaction: N₂ + 3H₂ → 2NH₃, calculate the mass of ammonia (NH₃) produced when 14 g of nitrogen react with hydrogen? (2 s.f.)
Relative formula mass values: (N₂ = 28) & (NH₃ = 17)
To help you plan your 10 combined science lesson on: Mass in a chemical reaction: using moles, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 combined science lesson on: Mass in a chemical reaction: 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 combined science lessons from the Calculations involving masses unit, dive into the full secondary combined science curriculum, or learn more about lesson planning.