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Lesson · Grade 11 · Chemistry

Writing Dissociation Equations

  • Grade 11
  • Chemistry
  • 1 min 56 s
  • British Columbia
  • BC11-SC-37

A labelled diagram builds up one row at a time: NaCl(s) → Na⁺(aq) + Cl⁻(aq), then CaCl₂(s) → Ca²⁺(aq) + 2 Cl⁻(aq), then Al₂(SO₄)₃(s) → 2 Al³⁺(aq) + 3 SO₄²⁻(aq). Along the way it explains state symbols, cations and anions, how a subscript becomes a coefficient, and why sulfate stays whole instead of splitting into S and O. Each row ends with a check that the charges add to zero, a solubility table column ticks all three compounds as dissolving well, and the video ends on a one-line recap.

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In one sentence

The question this lesson answers

What happens to table salt, sodium chloride, when it dissolves in water?

It is an ionic compound, made of positive and negative ions. In water the ions separate. This is called dissociation.

Transcript

What the lesson says

What happens to table salt, sodium chloride, when it dissolves in water?

It is an ionic compound, made of positive and negative ions. In water the ions separate. This is called dissociation.

The state symbol s means solid, and a q, short for aqueous, means dissolved in water.

The positive ion is called a cation, and the negative ion is an anion.

Check the charges: plus one and minus one add to zero, as the compound has no overall charge.

Next, calcium chloride. The small 2 is a subscript: two chloride ions for each calcium ion.

So it splits into one calcium ion, with a charge of plus two, and two chloride ions.

The 2 in front is a coefficient. It counts the ions.

Plus two from calcium and minus two from the two chloride ions add to zero.

Now aluminum sulfate. Sulfate is a polyatomic ion: a group of bonded atoms with an overall charge.

The subscripts give two aluminum ions, each plus three, and three sulfate ions, each minus two.

Sulfate stays together. It does not split into sulfur and oxygen.

Two aluminum ions give plus six, and three sulfate ions give minus six: zero again.

A solubility table shows which ionic compounds dissolve well in water, and all three of these do.

To write a dissociation equation, split the compound into ions, keep polyatomic ions whole, and check the charges add to zero.

Curriculum

Where this fits

British Columbia, Grade 11

Chemistry 11, Solutions: solubility of molecular and ionic compoundsBC11-SC-37

Previous: Ionic compounds split into ions; molecular ones stay wholeNext: Molarity: moles of solute per litre of solution

The outcomes and strands follow the British Columbia curriculum.

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