Balanced ionic equations - Higher

A balanced ionic equation shows the reacting ions in a chemical reaction. These equations can be used to model what happens in precipitation reactions.

Precipitation reactions

In a typical precipitation reaction, two soluble reactants form an insoluble product and a soluble product.

For example, silver nitrate solution reacts with sodium chloride solution. Insoluble solid silver chloride and sodium nitrate solution form:

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

The Na+ ions and NO3- ions remain separate in the sodium nitrate solution and do not form a precipitate. Ions that remain essentially unchanged during a reaction are called spectator ions.This means you can ignore them when you write the ionic equation. You only need to model how the solid silver chloride forms:

Ag+(aq) + Cl-(aq) → AgCl(s)

In a balanced ionic equation:

  • the number of positive and negative charges is the same
  • the numbers of atoms of each element on the left and right are the same
Question

Explain why this ionic equation is balanced: Ba2+(aq) + SO42-(aq) → BaSO4(s)

There are the same numbers of atoms of each element on both sides of the equation. The total charge on both sides is also the same (zero).

Question

Balance this ionic equation, which models the formation of a silver carbonate precipitate: Ag+(aq) + CO32-(aq) → Ag2CO3(s)

2Ag+(aq) + CO32-(aq) → Ag2CO3(s)

Question

Balance this ionic equation, which models the formation of an aluminium hydroxide precipitate: __Al3+(aq) + __OH-(aq) → Al(OH)3(s)

Al3+(aq) + 3OH-(aq) → Al(OH)3(s)

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