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Year 10 - Science

Deducing an empirical formula experimentally

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 and carry out an experiment to determine the empirical formula of a simple compound.

Key Notes

  • Small masses of a substance, including magnesium, can be easily heated in a crucible.
  • The crucible needs to be opened periodically to allow air (i.e. oxygen) to enter the apparatus.
  • Lifting a crucible lid too often or for too long may lead to loss of product (i.e. lower final mass recorded).
  • Using practical data and conservation of mass, chemists can calculate unknown reactant masses.
  • Reactant masses can determine the empirical formula of a substance, including the ionic ratio of a metal and oxygen.

Vocabulary To Learn

  • empirical formula: A substance's empirical formula shows the simplest whole number ratio of atoms of each element in a compound.
  • relative atomic mass: Relative atomic mass is the mean mass of an atom relative to 1/12th the mass of an atom of carbon–12.
  • evaluate: To evaluate something is to make a judgement about it with respect to a particular purpose.
  • 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 Mistakes To Avoid

  • Pupils think that simply ensuring a fair test will improve data collecting in a practical.

3 Quick Questions (With Answers)

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

Small masses of a substance, including magnesium, can be easily heated in a crucible. The crucible needs to be opened periodically to allow air (i.e. oxygen) to enter the apparatus.

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

A substance's empirical formula shows the simplest whole number ratio of atoms of each element in a compound. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Pupils think that simply ensuring a fair test will improve data collecting in a practical. Correction: Evaluating a practical is an often overlooked skill. Challenge pupils to focus on the equipment chosen and/or the method followed to consider how better data might be collected.

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