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Next exam on November 14 – 15, 2026:
All concepts

Ionic Reactions and Ion Coexistence

离子反应与离子共存

The conditions under which an ionic reaction proceeds, what an ionic equation reveals about composition, and judging whether ions can coexist under stated conditions.

4 real-exam questions · 3 sittings8 in mock papers19 practice

Formulas

  • Charge conservation in ionic equations

    Law
    ∑qleft=∑qright\sum q_{\text{left}}=\sum q_{\text{right}}

    Applies when：Total charge must match on both sides; an ionic equation is balanced only when charge and mass both are

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

  1. CSCA Chemistry April 2026 Past Paper
    The group of ions that can coexist in large amounts in an acidic solution and is colorless and transparent is ( ).
    • A. HCO3−\mathrm{HCO_{3}^{-}}, Na+\mathrm{Na^{+}}, Cl−\mathrm{Cl^{-}}, NO3−\mathrm{NO_{3}^{-}}
    • B. Ag+\mathrm{Ag^{+}}, K+\mathrm{K^{+}}, Cl−\mathrm{Cl^{-}}, NO3−\mathrm{NO_{3}^{-}}
    • C. Cu2+\mathrm{Cu^{2+}}, Na+\mathrm{Na^{+}}, SO42−\mathrm{SO_{4}^{2-}}, Cl−\mathrm{Cl^{-}}
    • D. Mg2+\mathrm{Mg^{2+}}, K+\mathrm{K^{+}}, Cl−\mathrm{Cl^{-}}, SO42−\mathrm{SO_{4}^{2-}}
    Show answer & solution

    Answer: D

    Answer: D Mg2+\mathrm{Mg^{2+}}, K+\mathrm{K^{+}}, Cl−\mathrm{Cl^{-}}, and SO42−\mathrm{SO_{4}^{2-}} can coexist in large amounts in an acidic solution and the solution is colorless. (In A, HCO3−\mathrm{HCO_{3}^{-}} reacts with H+\mathrm{H^{+}}; in B, Ag+\mathrm{Ag^{+}} reacts with Cl−\mathrm{Cl^{-}} to form a precipitate; in C, Cu2+\mathrm{Cu^{2+}} is blue and fails the colorless requirement.)
    Take the full CSCA Chemistry April 2026 Past Paper — timed & graded
  2. CSCA Chemistry March 2026 Past Paper
    Which ions coexist in large quantities in acidic solution?
    • A．Na+,OH−,Cl−,NO3−\mathrm { Na } ^ { + } , \mathrm { OH } ^ { - } , \mathrm { Cl } ^ { - } , \mathrm { NO } _ { 3 } { } ^ { - }
    • B．K+,CO32−,SO42−,Mg2+\mathrm { K } ^ { + } , \mathrm { CO } _ { 3 } { } ^ { 2 - } , \mathrm { SO } _ { 4 } { } ^ { 2 - } , \mathrm { Mg } ^ { 2 + }
    • C．NH4+,Al3+,SO42−,Cl−\mathrm { NH } _ { 4 } { } ^ { + } , \mathrm { Al } ^ { 3 + } , \mathrm { SO } _ { 4 } { } ^ { 2 - } , \mathrm { Cl } ^ { - }
    • D．Ba2+,NO3−,SO42−,Na+\mathrm { Ba } ^ { 2 + } , \mathrm { NO } _ { 3 } { } ^ { - } , \mathrm { SO } _ { 4 } { } ^ { 2 - } , \mathrm { Na } ^ { + }
    Show answer & solution

    Answer: C

    A: OH−\mathrm { OH } ^ { - }reacts with H+\mathrm { H } ^ { + } . B:CO32−\mathrm { B } : \mathrm { CO } _ { 3 } { } ^ { 2 - } reacts. D:Ba2++SO42−\mathrm { D } : \mathrm { Ba } ^ { 2 + } + \mathrm { SO } _ { 4 } { } ^ { 2 - } precipitate. C : all compatible ✓\checkmark. Answer: C.
    Take the full CSCA Chemistry March 2026 Past Paper — timed & graded

Real-exam evidence

Recorded past-paper appearances are listed below; online verification is labelled separately.

4 questions across 3 sittings0 of 3 sittings available to verify free online
  • CSCA Chemistry April 2026 Past Paper1 questionreading page not yet public
  • CSCA Chemistry March 2026 Past Paper1 questionreading page not yet public
  • CSCA Chemistry January 2026 Past Paper2 questionsreading page not yet public

8 questions across 5 mock papers — our own papers, so a coverage signal rather than real-exam evidence

19 related practice questions availablePractise free: Ionic Reactions and Tests

Sitting evidence comes from the CSCA past papers on record; questions whose original paper is missing are excluded, and sprint papers are deliberately not counted.

Related concepts

Redox Reactions