View source for Testing for Aqueous Ions

==Key Stage 4==
===Meaning===
'''Testing for aqueous ions''' is a set of techniques used to identify the [[ion]]s in a [[compound]].

===About Testing For Aqueous Ions===
[[Aqueous]] [[ion]]s can be identified through [[Chemical Reaction|chemical reaction]]s which [[product|produce]]:
*A [[precipitate]] - Which can indicate [[Metal Ion]]s, [[Halide]] [[ion]]s or [[Sulphate]] [[ion]]s.
*A [[gas]]  - [[Carbon Dioxide]] [[gas]] indicates [[Carbonate]] [[ion]]s.
: [[Metal Ion]]s are [[Positive Ion]]s and referred to as [[Cation]]s because they would collect at the [[Cathode]] in an [[electrolysis]] [[Chemical Reaction|reaction]].
: There are many different [[Negative Ion]]s and these are referred to as [[Anion]]s because they would collect at the [[Anode]] in an [[electrolysis]] [[Chemical Reaction|reaction]].

===Testing for Aqueous Metal Cations===
The test for [[aqueous]] [[metal]] [[cation]]s is done by adding [[Sodium Hydroxide]] to the [[solution]].
The following [[Chemical Reaction|reaction]]s occur to [[product|produce]] identifiable [[precipitate]]s:
====Iron(II) Ions====
<math>FeCl_2(aq) + 2NaOH(aq) → 2NaCl(aq) + Fe(OH)_2(s)</math>
: A light green [[precipitate]] is formed.
====Iron(III) Ions====
<math>FeCl_3(aq) + 3NaOH(aq) → 3NaCl(aq) + Fe(OH)_3(s)</math>
: A red-brown [[precipitate]] is formed.
====Copper(II) Ions====
<math>CuCl_2(aq) + 2NaOH(aq) → 2NaCl(aq) + Cu(OH)_2(s)</math>
: A light blue [[precipitate]] is formed.
====Magnesium, Calcium and Aluminium Ions====
<math>MgCl_2(aq) + 2NaOH(aq) → 2NaCl(aq) + Mg(OH)_2(s)</math>

<math>CaCl_2(aq) + 2NaOH(aq) → 2NaCl(aq) + Ca(OH)_2(s)</math>
: Both [[product|produce]] a white [[precipitate]] but can then be identified with a [[Flame Test]].

<math>AlCl_3(aq) + 3NaOH(aq) → 3NaCl(aq) + Al(OH)_3(s)</math>
: A white [[precipitate]] is formed but can be distinguished form [[Magnesium]] and [[Calcium]] by adding excess [[Sodium Hydroxide]] which causes the [[precipitate]] to [[dissolve]].

===Testing for Aqueous Anions===
====Halides====
The test for [[Halide]] [[anion]]s begins by adding dilute [[Nitric Acid]] to remove any possible [[Carbonate]]s. Then [[Silver Nitrate]] is added to form a [[precipitate]] of [[Silver Halide]].

<math>NaCl(aq) + AgNO_3(aq) → NaNO_3(aq) + AgCl(s)</math>

: A white [[precipitate]] is formed.

<math>NaBr(aq) + AgNO_3(aq) → NaNO3(aq) + AgBr(s)</math>

: A cream coloured [[precipitate]] is formed.

<math>NaI(aq) + AgNO_3(aq) → NaNO3(aq) + AgI(s)</math>

: A yellow [[precipitate]] is formed.

====Sulphates====
The test for [[Sulphate]] [[anion]]s begins by adding dilute [[Hydrochloric Acid]] to remove any possible [[Carbonate]]s. Then [[Barium Chloride]] is added to form a [[precipitate]] of [[Barium Sulphate]].
<math>Na_2SO_4(aq) + BaCl_2(aq) → 2NaCl(aq) + BaSO_4(s)</math>
: A white [[precipitate]] is formed.
====Carbonates====
The test for [[carbonate]] [[anion]]s begins by adding [[Hydrochloric Acid]] to the [[solution]]. This [[product|produces]] a [[gas]] which is collected and bubbled through [[Limewater]] to identify if [[Carbon Dioxide]] has been [[product|produced]]. If [[Carbon Dioxide]] has been [[product|produced]] then the [[Limewater]] will turn from [[transparent]] to cloudy.

<math>Na_2CO_3(aq) + 2HCl(aq) → 2NaCl(aq) + H_2O(l) + CO_2(g)</math>

: A [[gas]] is [[product|produced]] and bubbled through [[Limewater]].

<math>CO_2(g) + CaO(aq) → CaCO_3(s)</math>

: The [[Calcium Carbonate]] makes the [[Limewater]] appear cloudy.