Problem 23 - A Complete Resource Book in Chemistry for JEE Main

Question

A metal ion \(\mathrm{M}^{3+}\) loses three electrons to produce another cation. The oxidation number of the metal in the cation is (a) \(+3\) (b) \(+4\) (c) \(-3\) (d) \(+6\)

Step-by-Step Solution

Answer

(d) +6

Step 1: Understanding the Problem

We have a metal ion \( \mathrm{M}^{3+} \) that already signifies the metal \( M \) has lost three electrons to become positively charged by three units. We need to find the oxidation number after it loses three more electrons to become another cation.

Step 2: Determine the Charge after Electron Loss

Since the \( \mathrm{M}^{3+} \) ion loses three more electrons, it will have a total loss of 6 electrons. Each electron lost corresponds to a unit increase in oxidation number, so the charge of the new cation is \( +6 \).

Step 3: Assign the Oxidation Number

The oxidation number of an ion is equal to its charge. Therefore, the oxidation number of the new cation \( \mathrm{M}^{6+} \) is \( +6 \).

Key Concepts

Understanding Metal Ions

Metal ions are atoms that have lost or gained electrons, resulting in a net charge. Because metals are typically found on the left side of the periodic table, they tend to lose electrons easily. This loss of electrons turns the metal atom into a positively charged ion, often referred to simply as a 'cation'.
The number associated with the ion, like the "+3" in \(\mathrm{M}^{3+}\), indicates the oxidation number or the charge due to the loss of electrons. A metal ion with a charge of "+3" has lost three of its original electrons. This is common in many transition metals, which can exhibit multiple positive charges due to their ability to lose different numbers of electrons under various conditions.

• Metal atoms become cations when they lose electrons.
• The number of lost electrons equals the positive charge of the ion.
• Transition metals often exhibit variable charges.

Understanding these principles helps us to determine changes when additional electron transactions occur.

Exploring Electron Loss

Electron loss is a key concept when discussing oxidation in chemistry, especially with metal atoms. When an atom loses electrons, it undergoes oxidation, a process opposite to reduction, where electrons are gained. In the context of metal ions, electron loss increases the positive charge.
For example, in the given problem, a metal ion \(\mathrm{M}^{3+}\) has already lost 3 electrons. If it loses 3 more, the result is a 6-electron loss. Consequently, the cation becomes \(\mathrm{M}^{6+}\) indicating its new increased charge.

• Electron loss correlates directly to an increase in positive charge.
• Metal ions can further lose electrons to increase their oxidation number.
• The process of losing electrons is what defines oxidation.

In essence, understanding electron loss is pivotal for determining the behavior of metal ions in reactions.

Understanding Oxidation States

An oxidation state, often known as an oxidation number, expresses the overall charge of an atom or ion after the transfer of electrons. It's an essential concept in understanding redox reactions, which involve the transfer of electrons between substances.
Each oxidation state directly corresponds to the number of electrons an atom loses or gains. For an ion such as \(\mathrm{M}^{6+}\), this number shows the atom has lost 6 electrons, thus increasing its oxidation state. As atoms lose electrons, their oxidation state becomes more positive.

• Oxidation state indicates the degree of oxidation of an atom.
• Positive oxidation states occur due to electron loss.
• In any ion, the oxidation number equals the net charge of the ion.

Recognizing how oxidation states change as electrons are transferred allows us to predict and explain chemical behavior.