Reactions of ions in aqueous solution: Practice Questions

Which observation is made when aqueous sodium carbonate, \(\text{Na}_2\text{CO}_3(\text{aq})\), is added to an aqueous solution of iron(III) chloride, \([\text{Fe}(\text{H}_2\text{O})_6]^{3+}(\text{aq})\)?

A series of tests was performed on separate portions of an unlabelled aqueous solution containing a single metal-aqua ion, omath[\(\text{M}(\text{H}\)_2\(\text{O})\)_6\(]^{n+} omath, where\) \(\text{M}\) is either \(\text{Fe}\), \(\text{Cu}\), or \(\text{Al}\).

• Test 1: Addition of a few drops of aqueous \(\text{NaOH}\) produced a precipitate. When excess aqueous \(\text{NaOH}\) was added, the precipitate dissolved to give a colourless solution.
• Test 2: Addition of aqueous \(\text{Na}_2\text{CO}_3\) produced a white precipitate and vigorous effervescence.
• Test 3: Addition of excess concentrated aqueous \(\text{NH}_3\) gave a white precipitate that did not dissolve.

Which metal-aqua ion is present in the solution, and what is the formula of the species in the colourless solution formed in Test 1?

A solution containing an unknown metal aqua cation, \([\text{M}(\text{H}_2\text{O})_6]^{n+}\), is divided into two portions.

• Portion 1: Addition of aqueous sodium hydroxide gives a white precipitate P. Adding excess aqueous sodium hydroxide causes precipitate P to dissolve to form a colourless solution containing ion Q.
• Portion 2: Addition of aqueous sodium carbonate gives precipitate P and effervescence of a gas that turns limewater milky.

What are the identities of precipitate P and complex ion Q?

What is observed when a few drops of aqueous sodium hydroxide are added to an aqueous solution containing \([\text{Fe}(\text{H}_2\text{O})_6]^{2+}\) ions and the mixture is allowed to stand in air?

Which of the following represents a balanced ionic equation for the reaction of \([\text{Fe}(\text{H}_2\text{O})_6]^{3+}(\text{aq})\) with aqueous sodium carbonate?

Write an ionic equation to show the reaction occurring when aqueous sodium hydroxide is added dropwise to an aqueous solution of hexaaquairon(II) ions, \([\text{Fe}(\text{H}_2\text{O})_6]^{2+}\).

Explain why an aqueous solution containing \([\text{Fe(H}_2\text{O)}_6]^{3+}\) is more acidic than an aqueous solution containing \([\text{Fe(H}_2\text{O)}_6]^{2+}\).

Write a balanced ionic equation for the reaction that occurs when solid aluminium hydroxide, \(\text{Al}(\text{OH})_3(\text{H}_2\text{O})_3\), dissolves in excess dilute hydrochloric acid.

A sample of a metal sulfate contains the cation \(\text{M}^{3+}\). When aqueous ammonia, \(\text{NH}_3(\text{aq})\), is added dropwise until in excess to a solution containing \([\text{M}(\text{H}_2\text{O})_6]^{3+}\), a coloured precipitate is observed.

(a) State the formula of the precipitate formed when dilute aqueous ammonia is added to \([\text{Fe}(\text{H}_2\text{O})_6]^{3+}(\text{aq})\).
(b) State the colour of this precipitate.
(c) State what is observed when excess aqueous ammonia is added to this precipitate.

Aqueous solutions containing transition metal-aqua ions undergo characteristic reactions when mixed with aqueous sodium carbonate, \(\text{Na}_2\text{CO}_3\).

(a) Write a balanced ionic equation for the reaction of \([\text{Fe}(\text{H}_2\text{O})_6]^{2+}(\text{aq})\) with aqueous sodium carbonate, and state the observation made.

(b) Write a balanced ionic equation for the reaction of \([\text{Fe}(\text{H}_2\text{O})_6]^{3+}(\text{aq})\) with aqueous sodium carbonate, and state two distinct observations made.

(c) Explain why \([\text{Fe}(\text{H}_2\text{O})_6]^{3+}\) reacts differently from \([\text{Fe}(\text{H}_2\text{O})_6]^{2+}\) with carbonate ions.