Question

Do you expect dillerent products in soluuon when aluminium(III) chloride and potassium chloride treated separately with (i) normal water (ii) acidified water. and (iii) alkaline water? Write equations wherever necessary.

Short answer

Yes, aluminium chloride and potassium chloride form different products with normal, acidified, and alkaline water.

Step-by-step solution

Understanding the Reaction with Water

When aluminium(III) chloride is treated with water, it undergoes hydrolysis to form aluminium hydroxide and hydrochloric acid (HCl). The reaction can be described by the equation: \[ \text{AlCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{Al(OH)}_3 + 3\text{HCl} \]For potassium chloride, dissolving in water does not cause hydrolysis. It simply dissolves to give potassium and chloride ions:\[ \text{KCl} \rightarrow \text{K}^+ + \text{Cl}^- \]

Reaction in Acidified Water

In acidified water, the reaction of aluminium(III) chloride is influenced by the presence of excess protons. The hydrolysis still occurs, but the aluminium hydroxide is more soluble in acidic solutions, continuing its presence in the dissolved form as \text{Al}^{3+} ions. The equation remains largely unchanged:\[ \text{AlCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{Al(OH)}_3 (\text{dissolved}) + 3\text{HCl} \]Potassium chloride does not react further other than dissolving to form ions, similar to normal water.

Reaction in Alkaline Water

In alkaline water, aluminium(III) chloride forms aluminium hydroxide more rapidly, and due to the alkalinity, it can further react to form soluble \text{[Al(OH)}_4\text{]}^- complex ions:\[ \text{AlCl}_3 + 3\text{H}_2\text{O} + \text{OH}^- \rightarrow \text{[Al(OH)}_4\text{]}^- \]Potassium chloride will simply dissolve as before, as it does not undergo any further reaction in alkaline solutions.

Comparing Results

The products vary due to the hydrolyzing behavior of aluminium chloride and the inertness of potassium chloride: - In normal water, aluminium forms aluminium hydroxide; potassium forms simple ions. - In acidified water, aluminium remains dissolved in acidic conditions, while potassium again forms ions. - In alkaline water, aluminium might form a soluble aluminate complex; potassium remains as ions.

Key concepts

Hydrolysis of Aluminium Chloride

When aluminum chloride (\(\text{AlCl}_3\)) meets water, an interesting transformation happens called hydrolysis. This is due to the interaction between water molecules and the aluminum chloride, leading to the formation of new products. In simple water, aluminum chloride splits into aluminum hydroxide (\(\text{Al(OH)}_3\)) and hydronium ions, which eventually form hydrochloric acid (\(\text{HCl}\)). The chemical equation for this reaction is:
\[ \text{AlCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{Al(OH)}_3 + 3\text{HCl} \]
This reaction highlights how the aluminum component interacts with water to form a solid hydroxide while releasing chloride ions that bond with water's hydrogen to create hydrochloric acid.

• In neutral water, insoluble aluminum hydroxide precipitates.
• In acidic water, \(\text{HCl}\) keeps the aluminum in solution as \(\text{Al}^{3+}\) ions, preventing precipitation.
• In alkaline water, \(\text{OH}^-\) ions enhance hydrolysis forming soluble aluminum complex ions like \([\text{Al(OH)}_4]^-\).

Dissolution of Potassium Chloride

Potassium chloride (\(\text{KCl}\)) behaves quite differently compared to aluminum chloride. When it is introduced to water, there is no chemical reaction taking place beyond dissolving. This process is called "dissolution," where \(\text{KCl}\) separates into its constituent ions in water.
The simple equation
\[ \text{KCl} \rightarrow \text{K}^+ + \text{Cl}^- \]
represents this process, showcasing how potassium and chloride ions disperse uniformly in water.

• There's no chemical change; \(\text{KCl}\) only dissociates into ions.
• This behavior is consistent regardless if the water is neutral, acidic, or alkaline.
• The ions \(\text{K}^+\) and \(\text{Cl}^-\) do not undergo further reactions either in acidic or alkaline environments.

Effect of pH on Chemical Reactions

The pH of a solution significantly affects the nature of chemical reactions. pH measures the acidity or basicity of a solution and directly influences how compounds like aluminum chloride hydrolyze in water.

• In neutral solutions, compounds behave in their default manner, dictated by their inherent properties such as solubility and dissociation.
• In acidic solutions (low pH), an excess of \(\text{H}^+\) ions can prevent precipitations that would normally occur by keeping components dissolved.
• In alkaline solutions (high pH), \(\text{OH}^-\) ions can promote additional reactions like forming complex ions, which changes the solubility behavior of substances.

Therefore, manipulating pH allows for control over reaction pathways and products, a vital concept in fields like environmental chemistry and industrial processes.