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Year 10 - Science

Determining an equation experimentally: magnesium oxide

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 describe a safe experiment to calculate the reacting molar ratios for the oxidation of magnesium.

Key Notes

  • Heating magnesium in a crucible will react it with oxygen.
  • The crucible must be opened periodically to ensure enough oxygen enters the vessel to completely oxidise the magnesium.
  • Opening the crucible too much will cause mass/product loss.
  • Safety precautions should be taken when burning magnesium because of the bright light produced.
  • The stoichiometry for a reaction can be calculated given experimental data.

Vocabulary To Learn

  • limiting reactant: the reactant that completely reacts, thereby determining the maximum amount of product that can be formed in a chemical reaction. All other reactants will be present in excess
  • ratio: used to determine the size of one quantity in relation to another
  • stoichiometry: the molar ratio of the reactants and products in a chemical reaction
  • mole: A 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.
  • balanced symbol equation: describes a reaction using a symbol equation with coefficients which ensure there are equal numbers of atoms of each element on both sides of the equation

Common Mistakes To Avoid

  • Pupils sometimes struggle to understand that 'heating to constant mass' takes time and multiple measurements.

3 Quick Questions (With Answers)

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

Heating magnesium in a crucible will react it with oxygen. The crucible must be opened periodically to ensure enough oxygen enters the vessel to completely oxidise the magnesium.

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

the reactant that completely reacts, thereby determining the maximum amount of product that can be formed in a chemical reaction. All other reactants will be present in excess. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Pupils sometimes struggle to understand that 'heating to constant mass' takes time and multiple measurements. Correction: Link the idea that atoms rearrange during a reaction and that for all atoms of a substance to be oxidised, enough oxygen must be present. If the product measurements show a 'constant mass' we can be confident that complete oxidation has occurred.

More Lessons In This Unit

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