Question

When a piece of sodium metal is dropped in water, hydrogen gas evolved because (a) sodium is reduced and acts as an oxidising agent (b) water is oxidised and acts as a reducing agent (c) sodium loses electrons and is oxidised while water in reduced (d) water loses electrons and is oxidised to hydrogen.

Short answer

The correct answer is (c) sodium loses electrons and is oxidised while water is reduced.

Step-by-step solution

Understanding Redox Reactions

To solve this exercise, we need to understand the concept of redox (reduction-oxidation) reactions. In a redox reaction, one reactant is reduced by gaining electrons, and another is oxidized by losing electrons.

Analyzing the Reaction of Sodium with Water

When sodium reacts with water, the reaction is as follows: Sodium (Na) loses electrons to form Na+ ions, and water (H2O) gains electrons to form OH- ions and hydrogen gas (H2).

Identifying the Oxidizing and Reducing Agents

The substance that gets oxidized loses electrons, and thus is the reducing agent, while the substance that gets reduced gains electrons and is the oxidizing agent. Therefore, sodium, which loses electrons, is oxidized and acts as a reducing agent. Water gains those electrons, and therefore, is reduced and acts as an oxidizing agent.

Selecting the Correct Option

Based on our analysis, the correct option describes sodium being oxidized (losing electrons), and water being reduced. Thus, the correct answer is option (c) sodium loses electrons and is oxidised while water is reduced.

Key concepts

Oxidation and Reduction

Let's dive into the intriguing world of redox reactions, where every chemical player has a role, either gaining or giving up electrons. Oxidation is the act of losing electrons. When a molecule, atom, or ion parts with electrons, it is said to be oxidized. On the other side of the coin, we have reduction, the process of electron gain. For every oxidation event, there's a reduction one happening somewhere else - they're two halves of the same whole, always occurring together in what we call a redox reaction.

In simpler terms, think of it as a dance of electrons where one partner, the oxidizing agent, encourages another, the reducing agent, to give up its electrons. The oxidizing agent thereby gets ‘reduced’ as it gains electrons, and the reducing agent gets ‘oxidized’ as it loses electrons. Remember this: OIL RIG - Oxidation Is Loss, Reduction Is Gain. Identifying which reactants are ‘dancing’ which part in the reaction is key to understanding the overall chemical process.

Chemical Properties of Sodium

Sodium, a member of the alkali metals on the periodic table, is a fascinating element with unique properties that influence how it reacts chemically. Sodium is a soft, silvery-white metal under standard conditions, and it's highly reactive, especially with water.

Why so reactive? It’s all thanks to its single electron in the outer shell desperately seeking to leave and join a more stable structure, such as a noble gas configuration. This propensity to lose its lonely valence electron makes sodium a prime candidate for playing the role of a reducing agent in redox reactions.

Another intriguing trait is sodium's low density, only about 0.97 grams per cubic centimeter, which allows it to float on water. Add sodium to the conversation with water, and you'll ignite a reaction that vividly demonstrates sodium's eagerness to donate electrons and react with the elements in its vicinity.

Reaction of Sodium with Water

When sodium meets water, it's not just a splash, it's a whole show! This highly exothermic reaction is a perfect example of a redox reaction. As we've learned, sodium is ready to lose that valence electron, and water is an excellent electron acceptor. So what happens when these two react?

Chemically speaking, we have the equation: \( 2 Na + 2 H_2O \rightarrow 2 Na^+ + 2 OH^- + H_2 \) Sodium (\( Na \) atoms) donates electrons to form \( Na^+ \) ions, while water molecules receive those electrons, forming hydroxide ions (\( OH^- \) ions) and liberating hydrogen gas (\( H_2 \)). The \( Na^+ \) and \( OH^- \) ions remain dissolved in water, forming a basic solution.

The hydrogen gas evolved may ignite due to the heat of the reaction, causing a pop or even a small flame. It's a dramatic demonstration of sodium's chemical properties, highlighting its role as a reducing agent and showcasing the joint dance of oxidation and reduction.