Lesson 4C.1

4C.1 Tests for identifying inorganic ions Quiz: Pearson Edexcel Chemistry, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4C.1, Tests for identifying inorganic ions: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 4: Inorganic Chemistry and the Periodic Table, written with Revision Ninja.

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The 20 questions

  1. Which reagent identifies carbonate ions, CO3 2-?

    • Barium chloride, which gives a cream precipitate with carbonate ions in the solution being tested
    • Silver nitrate, which gives a yellow precipitate with carbonate ions in the solution being tested
    • Sodium hydroxide, which gives a gas that turns litmus blue with carbonate ions in the solution being tested
    • Dilute acid, which gives carbon dioxide that turns limewater milky

  2. What is the ionic equation for the reaction of carbonate ions with acid?

    • CO3 2- + 2H+ -> CO2 + 2H2
    • CO3 2- + H+ -> HCO3-
    • CO3 2- + 2H+ -> CO2 + H2O
    • CO3 2- + H+ -> CO2 + OH-

  3. Which reagent confirms the presence of sulfate ions, SO4 2-?

    • Sodium hydroxide, which gives off ammonia gas from the solution containing the sulfate ions being tested
    • Acidified barium chloride solution, giving a white precipitate
    • Acidified silver nitrate, which gives a white precipitate with sulfate ions in the solution being tested
    • Dilute acid, which gives off carbon dioxide gas from the solution containing the sulfate ions being tested

  4. What is the ionic equation for the test for sulfate ions?

    • BaCl2 + SO4 2- -> BaSO4 + 2Cl-
    • Ba + SO4 -> BaSO4
    • Ba2+ + SO4 2- -> BaSO4
    • Ba2+ + 2SO4 2- -> Ba(SO4)2

  5. Which test identifies ammonium ions, NH4+?

    • Add dilute acid, and a gas is released that turns limewater milky in the test tube of the sample
    • Add acidified barium chloride, and a white precipitate forms in the test tube containing the sample
    • Add silver nitrate, and a cream precipitate forms in the test tube containing the sample solution
    • Warm with sodium hydroxide, and ammonia gas turns damp red litmus paper blue

  6. What is the ionic equation for the test for ammonium ions?

    • NH4+ + Cl- -> NH3 + HCl
    • NH4+ + H+ -> NH3 + H2
    • NH4+ + OH- -> NH3 + H2O
    • NH4+ + OH- -> NH4OH2

  7. Which reagent is used to test for halide ions, and what does it show?

    • Barium chloride, which forms a yellow precipitate with the halide ions and so identifies the halide in the sample
    • Acidified silver nitrate, which forms a precipitate that identifies the halide
    • Sodium hydroxide, which forms a cream gas with the halide ions and so identifies the halide in the sample
    • Dilute acid, which forms a precipitate with the halide ions and so identifies the halide in the sample

  8. Which silver halide precipitate is yellow?

    • Silver fluoride
    • Silver iodide
    • Silver bromide
    • Silver chloride

  9. Why is dilute nitric acid added before silver nitrate in a halide test?

    • To release ammonia from the sample, which then identifies the halide by its distinctive smell and colour
    • To make the solution basic so that the silver halides form more readily and settle out of the solution
    • To dissolve the silver halide precipitate once it forms, so that the halide can be identified by its colour
    • To remove carbonate or other ions that would form a precipitate and confuse the result

  10. Which reagent distinguishes carbonate from sulfate?

    • Dilute acid, which gives a gas with carbonate but no reaction with sulfate
    • Water, which dissolves only the carbonate and leaves the sulfate as an insoluble solid in the sample
    • Sodium hydroxide, which gives ammonia gas with both carbonate and sulfate ions in the solution being tested
    • Silver nitrate, which gives a white precipitate with both carbonate and sulfate ions in the solution being tested

  11. What is the observation when limewater is used to test carbon dioxide?

    • The limewater turns green
    • The limewater turns yellow
    • The limewater turns milky
    • The limewater turns blue

  12. What is observed in the test for sulfate with acidified barium chloride?

    • A cream precipitate forms
    • A gas with a pungent smell is released
    • A white precipitate forms
    • A yellow solution forms

  13. What is the ionic equation for the formation of the yellow precipitate in the iodide test?

    • Ag + I -> AgI
    • Ag+ + 2I- -> AgI2
    • Ag+ + I- -> AgI2
    • Ag+ + I- -> AgI

  14. Why are flame tests not suitable for identifying transition metal ions?

    • Many transition metal ions do not give distinctive flame colours, so the test is not reliable for them
    • Transition metals react with the flame to form water, which hides any colour that the metal ions might show
    • Transition metals burn in the flame with an invisible colour, which is why no colour can be observed in the test
    • Transition metal ions are always colourless in solution, so there is no colour to see in a flame test

  15. Which compound gives a positive test for carbonate ions when dilute acid is added?

    • Sodium sulfate, which reacts with dilute acid to give a gas that turns limewater milky in the test
    • Sodium chloride, which reacts with dilute acid to give a gas that turns limewater milky in the test
    • Sodium carbonate
    • Sodium nitrate, which reacts with dilute acid to give a gas that turns limewater milky in the test

  16. Which ionic equation represents the test for hydrogencarbonate ions?

    • HCO3- + H+ -> CO2 + H2O
    • HCO3- + Ba2+ -> BaCO3 + H+
    • HCO3- + Cl- -> HCl + CO2
    • HCO3- + OH- -> CO2 + H2O

  17. A solid gives a white precipitate with acidified barium chloride. Which conclusion is best supported?

    • The solid contains carbonate ions, since BaCO3 is soluble
    • The solid contains chloride ions, since BaCl2 is white
    • The solid contains nitrate ions, since barium nitrate is insoluble
    • The solid contains sulfate ions, since BaSO4 is insoluble

  18. Which test would identify a sample containing both carbonate and sulfate ions?

    • Add dilute acid to detect carbonate, then add acidified barium chloride to detect sulfate
    • Add water and filter to remove both ions, then test the solid that remains on the filter paper for identity
    • Add sodium hydroxide only and test for ammonia, which identifies both ions in the same single test
    • Add silver nitrate, which gives a yellow precipitate for both ions, so the sample can be identified in one step

  19. Explain why acidified barium chloride is used rather than barium chloride alone for the sulfate test.

    • Acid is needed to make barium chloride ionic, so that the barium ions can then react with the sulfate ions
    • Acid removes carbonate and other ions that would also form precipitates with barium, so the result is specific to sulfate
    • Acid releases sulfur dioxide gas that identifies the sulfate ion in the sample being tested by the method
    • Acid makes sulfate ions volatile so that they can be driven off and detected by the smell of the gas

  20. Explain why warming is needed in the test for ammonium ions.

    • Warming converts ammonium ions into nitrate ions, which are then detected by the silver nitrate test instead
    • Warming dissolves the solid sample completely so that the ammonium ions can be seen in the clear solution
    • Warming forms a precipitate of ammonium hydroxide, which is then filtered off and tested for identity
    • Warming drives off ammonia gas from the solution so that it can be detected

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