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Year 10 - Science

Mass in a chemical reaction: using moles

Calculations involving masses

Unit Summary

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.

Lesson Summary

You will learn to interpret a balanced symbol equation to predict the mass of either a reactant or a product.

Key Notes

  • 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).

Vocabulary To Learn

  • 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 Mistakes To Avoid

  • Pupils struggle to recall the order of steps required to mathematically process the available information in order to answer the question.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key 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).

2. Define this scientific word and use it in context. 'stoichiometry'

Stoichiometry refers to the molar ratio of the reactants and products in a chemical reaction. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Pupils struggle to recall the order of steps required to mathematically process the available information in order to answer the question. Correction: 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.

More Lessons In This Unit

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