Edexcel IAL Chemistry 8.19 Tests for carbonate, sulfate and ammonium ions

Choose the reagent sequence first, state the precise gas or precipitate observation and include aqueous and solid states when an ionic equation is requested.

Exam points

Use acid and limewater to identify carbonate or hydrogencarbonate from carbon dioxide.
Test sulfate with acidified barium solution and write the BaSO₄ precipitation equation.
Warm ammonium ions with NaOH and confirm NH₃ using damp red litmus or HCl fumes.

[Maximum number: 2]

Experiments were carried out on a sample of hydrated barium nitrate crystals, $\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}$ .

The white solid which remained in the test tube was allowed to cool to room temperature. Dilute hydrochloric acid was added to the solid and a solution formed.

This solution is used in a common laboratory test for an anion.
Give the formula of this anion and the positive result of the test.

Formula
Positive test result

An answer that makes reference to the following points:

(formula)

- $\mathrm{SO}_{4}{ }^{2-}$

(1)

(positive test result)

- white precipitate / white solid

(1)

Mark independently

Ignore name

Allow ionic equations that include $\mathrm{SO}_{4}{ }^{2-}$

Do not award other ionic equations

Allow white ppt(e)

Do not award if other chemical tests are mentioned If the precipitate is given as AgCl do not award this mark

(2)

Figure for Answer to Question 8.19—Reactions question 1 — Edexcel A-Level Chemistry AS

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8.19—Reactions question 1