Ionic equations
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The teaching part (2 min) is free to watch. A free account opens the whole lecture: 6 worked examples, 6 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Mix two clear solutions
- What is an ionic equation?
- Which substances are split into ions?
- Which ionic compounds are soluble?
- The method
Read the transcript of the teaching part
Last time
Before we start: last time, in Formulae of ionic compounds, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Mix two clear solutions
Mix a clear solution of silver nitrate with a clear solution of sodium chloride, and a white solid appears at once. Only some of the ions in the beaker take part. The others just watch. An ionic equation shows only the ions that really react.
What is an ionic equation?
A normal equation shows every substance. An ionic equation shows only the ions, atoms or molecules that change. The ions that are the same on both sides are called spectator ions. They take no part in the reaction, so we leave them out. An ionic equation must balance in two ways: the atoms, and the total charge.
Which substances are split into ions?
A dissolved ionic compound, marked aqueous, is written as separate ions. Solids, liquids, gases and water stay as formulae. They are not split up. So a precipitate, which is a solid, is written whole, with the symbol (s).
Which ionic compounds are soluble?
All sodium, potassium and ammonium salts are soluble. So are all nitrates. Chlorides are soluble, except silver chloride and lead chloride. Sulfates are soluble, except barium, calcium and lead. Carbonates and hydroxides are insoluble, except those of sodium, potassium and ammonium.
The method
First, write the balanced equation with state symbols. Second, split every aqueous ionic compound into its ions. Third, cross out the ions that are the same on both sides. These are the spectators. Fourth, write what is left, and check that atoms and charges balance.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Equations.
The whole chapter: Stoichiometry, Stoichiometry.
Chapter 3: Stoichiometry
- Relative formula mass 6 min
- Formulae of ionic compounds 6 min
- Writing and balancing equations 7 min
- Ionic equations 7 min
- The mole and the Avogadro constant 6 min
- Moles: amount, mass and molar mass 6 min
- Reacting masses 7 min
- Gas volumes at r.t.p. 7 min
- Concentration and titration calculations 9 min
- Percentage composition by mass 6 min
- Empirical and molecular formulae 7 min
- Water of crystallisation 7 min
Also for IGCSE Chemistry 0620
Which topics come up most in IGCSE Chemistry 0620 past papers, counted from every paper since 2004.