Describe and explain the method for testing a solution for the presence of carbonate ions.

  1. Add dilute nitric acid to the solution - effervescence suggests the presence of carbonate ions.
  2. Bubble the gas produced through limewater - a white precipitate confirms the presence of carbonate ions.


Carbon dioxide, produced in step 1, reacts with limewater (aqueous calcium hydroxide) to form a white precipitate of calcium carbonate. 

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What is the equation, including state symbols, for the reaction between carbon dioxide and limewater, Ca(OH)2?

CO2(g) + Ca(OH)2(aq) ➔ CaCO3(s) + H2O(l)

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Why are dilute sulfuric and hydrochloric acids unsuitable for testing the presence of carbonate ions?

Sulfuric and hydrochloric acids contain sulfate and chloride ions respectively, which can create false positive results if the solution is subsequently tested for the presence of sulfate or halide ions.


Therefore, nitric acid is used as the source of H+ ions instead.

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Describe the method for testing a solution for the presence of sulfate ions.

Add acidified Ba2+(aq) ions to the solution.

In the presence of sulfate ions, a white precipitate of barium sulfate forms.

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What is the ionic equation, including state symbols, for the formation of the precipitate in the sulfate ion test?

Ba2+(aq) + SO42-(aq) ➔ BaSO4(s)

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Describe the method for testing a solution for the presence of halide ions.

  • Add aqueous silver nitrate to the solution.
  • In the presence of a chloride ions, a white precicipitate of silver chloride is formed.
  • In the presence of a bromide ions, a cream precicipitate of silver bromide is formed.
  • In the presence of an iodide ions, a yellow precicipitate of silver iodide is formed.

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What is the ionic equation, including state symbols, for the formation of the precipitate in the test for iodide ions?

Ag+(aq) + I-(aq) ➔ AgI(s)

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What reagent can be added to a silver halide precipitate to confirm its identity?

Aqueous ammonia, NH3(aq),


The identity of the halide ion in the precipitate can be confirmed because silver chloride, silver bromide, and silver iodide have different solubilities in ammonia.

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How can aqueous ammonia distinguish between precipitates of silver chloride and silver bromide?

Silver chloride redissolves in dilute aqueous ammonia but silver bromide remains insoluble.

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How can aqueous ammonia distinguish between precipitates of silver bromide and silver iodide?

Silver bromide redissolves in concentrated aqueous ammonia but silver iodide remains insoluble.

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State the correct order in which tests are conducted for the following negative ions: halide ions; sulfate ions; and carbonate ions.

The correct order of tests is:

  1. Carbonate ions
  2. Sulfate ions
  3. Halide ions

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