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Formulae, Equations and Amounts of Substance

Writing and balancing full and ionic equations

  • 3 things to know
  • Unit AS 1

Overview

Four state symbols and what each means, ionic equation and term spectator ion.

What you need to know

Answer each one before you reveal it.

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Key term

What must be true of both sides of a correctly balanced chemical equation?

Key term

Why can the formula of a compound never be altered to make an equation balance?

Key term

State the four state symbols and what each means.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What must be true of both sides of a correctly balanced chemical equation?

    Model answer

    The number of atoms of each element must be the same on both sides, and the total charge must be the same on both sides.

  2. 2

    Why can the formula of a compound never be altered to make an equation balance?

    Model answer

    The formula is fixed by the bonding in the substance, so only the large numbers in front of the formulae may be changed.

  3. 3

    State the four state symbols and what each means.

    Model answer

    The symbol (s) means solid, (l) means liquid, (g) means gas and (aq) means dissolved in water.

  4. 4

    Balance the combustion of ethane in oxygen.

    Model answer

    The balanced equation is 2C₂H₆(g) + 7O₂(g) → 4CO₂(g) + 6H₂O(l).

  5. 5

    Write the balanced equation for the reaction of sodium with water.

    Model answer

    The equation is 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g).

  6. 6

    What is an ionic equation?

    Model answer

    An ionic equation shows only the ions and species that actually take part in the reaction, with the spectator ions left out.

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