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Chapter 5: Problem 5

Give reasons for (a) Sodium reacts with water to liberate hydrogen while aluminium remains safe with water. (b) \(\mathrm{Co}^{3+}\) oxidises water (c) Organic-matter rich water-logged soil contains \(\mathrm{Fe}^{2+}\) ions while oxygen-rich water contains Fe ions

Short Answer

Expert verified
(a) Sodium is highly reactive and reacts with water to form NaOH and liberate H2. Aluminium is protected by a layer of oxide. (b) Co3+ ions oxidise water to stabilize their high oxidation state. (c) Enclosed water-logged soils lack oxygen which leads iron compound to get reduced to Fe2+, while oxygen-rich water will oxidize Fe2+ to iron oxide.

Step by step solution

01

Reason for Sodium Reaction

Sodium is a highly reactive metal. When it comes into contact with water, it reacts vigorously, liberating hydrogen gas and forming sodium hydroxide. Here's the chemical reaction: \[2\, \mathrm{Na} + 2\, \mathrm{H}_2\mathrm{O} \rightarrow 2\, \mathrm{NaOH} + \mathrm{H}_2\]\n
02

Reason for Aluminium Non-Reaction

Aluminium doesn't react with water because it forms a protective layer of aluminium oxide (Al2O3) which shields it from further reaction.
03

Reason for Co3+ Oxidizing Water

\(\mathrm{Co}^{3+}\) ions have a high oxidation state and, hence, oxidises water by taking electrons from water molecules to stabilize itself.
04

Reason for presence of Fe2+ in certain types of soil

In water-logged soils rich in organic matter, the soil lacks oxygen. In such conditions, iron may get reduced to \(\mathrm{Fe}^{2+}\), which is more soluble. In the case of oxygen-rich water, the presence of \(\mathrm{Fe}^{2+}\) is lower as it gets oxidized to \(\mathrm{Fe}^{3+}\), which is less soluble and precipitates out.

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Most popular questions from this chapter

Calculate the equilibrium constant for the possible reaction between \(\mathrm{Fe}^{2+}(\mathrm{aq})\) ions and \(\mathrm{Ce}^{4+}(\mathrm{aq})\) ions \(\mathrm{f} E_{\mathrm{Ce}^{4+} / \mathrm{ce}^{3+}}=1.44 \mathrm{~V}\) and \(E_{\mathrm{Fe}^{\circ} / \mathrm{Fe}^{2+}}^{\circ}=0.68 \mathrm{~V}\). Also comment on the spontaneity of the reaction.

Write short notes on (a) Redox stability field of water (b) Hydrogen overpotential (c) Nernst equation(d) Disproportionation

Discuss the Pourbaix diagram for iron in detail.

Define the following terms: (a) Oxidation (b) Standard electrod potential (c) Overpotential (d) Redox couple

Draw a Frost diagram for mercury in acid solution and comment on the tendency of the involved species to undergo disproportionation. Given \(E_{\mathrm{Hg}^{2+} / \mathrm{Hg}_{2}^{2+}}=0.911 \mathrm{~V}\) and \(E_{\mathrm{H}_{2}^{2+} / \mathrm{Hg}}^{\circ}=0.796 \mathrm{~V}\)
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