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O Levels Chemistry (5070)•5070/12/M/J/22
Question 12 from 5070/12/M/J/22

Explanation

Net Ionic Equation for Precipitation

Steps:

  • Write the molecular equation: 2AgNO₃(aq) + K₂CrO₄(aq) → Ag₂CrO₄(s) + 2KNO₃(aq).
  • Dissociate into total ionic: 2Ag⁺(aq) + 2NO₃⁻(aq) + 2K⁺(aq) + CrO₄²⁻(aq) → Ag₂CrO₄(s) + 2K⁺(aq) + 2NO₃⁻(aq).
  • Cancel spectator ions (K⁺ and NO₃⁻) that appear unchanged on both sides.
  • Result: 2Ag⁺(aq) + CrO₄²⁻(aq) → Ag₂CrO₄(s), matching option C.

Why C is correct:

  • It is the net ionic equation, showing only reacting species per solubility rules for precipitates.

Why the others are wrong:

  • A includes spectator ions and is the full molecular equation.
  • B is the total ionic equation without canceling spectators.
  • D has incorrect 1:1 stoichiometry and formula (Ag₂CrO₄ requires 2:1 ratio).

Final answer: C

Topic: Identification of ions and gases

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