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4.2Chemical Reactions

Net Ionic Equations — AP CHEMISTRY Revision Notes & Topical Questions

5 min read 8 parts Lesson 5 of 12 1 quiz

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4.2 Net Ionic Equations — Notes — AP CHEMISTRY notes: Write molecular, complete ionic and net ionic equations that are balanced for atoms and charge.All physical and chemical processes can be represented by balanced equations.A chemical change is a rearrangement of atoms, so ever…

  • Molecular equation
  • Complete ionic equation
  • Written as ions
  • Strong acids to know
  • Strong bases
  • Written as intact formulae

Section 1 of 8Balanced equations

Balanced equations
All physical and chemical processes can be represented by balanced equations.
A chemical change is a rearrangement of atoms, so every element has equal numbers of atoms on both sides.
The form of equation used depends on the context.

Section 2 of 8Three forms of equation

Molecular equation
Molecular equation shows all compounds as complete formulae.
Complete ionic equation
Complete ionic equation shows all strong electrolytes in aqueous solution as separate ions.
Net ionic equation
Net ionic equation shows only the species that actually change; spectator ions, present unchanged on both sides, are removed.

Section 3 of 8What is written as ions

What is written as ions
Written as ions
  • Written as ions soluble ionic compounds, strong acids and strong bases in solution.
Strong acids to know
  • HCl, HBr, HI, HNO3, H2SO4 and HClO4.
Strong bases
  • Group 1 hydroxides and the hydroxides of Ca, Sr and Ba.
Written as intact formulae
  • Written as intact formulae solids (precipitates), liquids such as H2O, gases, weak acids (HF, CH3COOH), weak bases (NH3) and molecular compounds.
Always soluble (AP expectation)
  • Always soluble (AP expectation) compounds of Na+, K+, NH4+ and all nitrates.

Section 4 of 8Writing a net ionic equation

1
Write the balanced molecular equation with state symbols.
2
Split strong electrolytes in solution into ions to give the complete ionic equation.
3
Cancel the spectator ions that appear unchanged on both sides.
4
Check that the equation is balanced for both atoms and charge.
  • If every ion is a spectator, no reaction occurs.

Section 5 of 8Examples

FormAgNO3 with NaCl
MolecularAgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
Complete ionicAg+ + NO3− + Na+ + Cl− → AgCl(s) + Na+ + NO3−
Net ionicAg+(aq) + Cl−(aq) → AgCl(s)
  • Strong acid with strong baseH+(aq) + OH−(aq) → H2O(l), or H3O+ + OH− → 2 H2O.

Section 6 of 8More from the specification

More from the specification
Precipitation of insoluble salts versus covalent bonds
  • Precipitation of insoluble salts versus covalent bonds spectator ions cancel out, while covalent bonds in molecular water remain intact.
Composition
  • What a substance or mixture is made of.
Covalent bond
  • A shared pair of electrons between two atoms, giving noble gas configurations.
Reactants
  • The substances that react together at the start of a reaction.
Product
  • A substance formed in a reaction.
Substance
  • A material with only one type of particle.
Coefficient
  • The number in front of a formula in a balanced equation.
Oxygen
  • A gas that relights a glowing splint.
Fraction
  • A group of hydrocarbons with similar chain length and boiling points.
Mixture
  • Two or more substances mixed but not chemically combined.
Matter
  • Everything you can see and feel; it exists as solid, liquid or gas.

Section 7 of 8Key terms

TermMeaning
Molecular equationEquation written with complete formulae.
Complete ionic equationEquation with strong electrolytes as separate ions.
Net ionic equationEquation showing only the species that react.
Spectator ionIon present unchanged on both sides of an equation.
Strong electrolyteSubstance that dissociates completely in water.
PrecipitateInsoluble solid formed in a reaction.

Section 8 of 8Exam technique

1
Writing precipitates, gases or weak electrolytes as separate ions
2
Leaving spectator ions in the net ionic equation
3
Balancing atoms but not charge
4
Splitting soluble ionic compounds into the wrong number of ions

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