Question

A metal \(X\) displaces nickel from nickel sulphate solution but does not displace manganese from manganese sulphate solution. What is the correct order of their reducing powers? (a) \(\mathrm{Ni}>\mathrm{Mn}>X\) (b) \(X>\mathrm{Mn}>\mathrm{Ni}\) (c) \(\mathrm{Mn}>X>\mathrm{Ni}\) (d) \(\quad \mathrm{Mn}>\mathrm{Ni}>X\)

Short answer

\(\mathrm{Mn}>X>\mathrm{Ni}\)

Step-by-step solution

Understanding Single Replacement Reactions

In a single replacement reaction, a more reactive metal can displace a less reactive metal from its compound. The reactivity of a metal is related to its ability to lose electrons, that is, its reducing power. A metal with higher reducing power can displace another metal with lower reducing power from its compound in solution.

Analyzing the Metal X

Metal X is able to displace nickel from nickel sulphate solution. This indicates that metal X has a higher reducing power than nickel. On the other hand, metal X does not displace manganese from manganese sulphate solution, which means manganese has a higher reducing power than metal X.

Determining the Order of Reducing Powers

Since metal X can displace nickel, it has a greater reducing power than nickel. However, because metal X cannot displace manganese, manganese must have a greater reducing power than metal X. Therefore, the order from greatest to least reducing power is \(\mathrm{Mn}>X>\mathrm{Ni}\).

Key concepts

Single Replacement Reaction

A single replacement reaction, also known as a substitution reaction, is a fundamental type of chemical reaction where an element replaces another element that is part of a compound. To visualize this, imagine a dance where couples are spinning around the floor. Suddenly, a new dancer joins in and cuts in on a couple, taking one partner away. In chemical terms, the 'new dancer' is the single element that replaces another element in a compound, forming a new compound in the process.

For example, when a metal atom comes into contact with a compound of another metal and an anion, the more reactive metal will 'cut in' and take the place of the less reactive metal, bonding with the anion. This switch is possible because the more reactive metal has a greater tendency to lose electrons and form positive ions. This leads to the displacement of the less reactive metal which is released as a free element.

In the context of our metal X displacing nickel from nickel sulphate, we have a clear scenario of a single replacement reaction. Metal X acts as the more reactive 'dancer,' effectively pushing nickel out of the dance to pair up with sulphate, leaving nickel as a single element.

Reactivity Series

The reactivity series is a ranking of metals based on their reactivity, or more specifically, their tendency to lose electrons and form positive ions. Think of it as a leaderboard for metals, where those at the top are the most willing to participate in reactions, such as giving away their electrons to form compounds. Reactivity can depend on various factors, including electronic configuration and the presence of other elements or compounds.

Metals at the top of the series are more reactive and possess greater reducing power. This means that they can more easily give up electrons, therefore they 'reduce' other substances. In our given exercise, this series helps us understand why metal X cannot displace manganese - manganese is higher than X in the series, signifying it has a stronger hold on the sulphate dance partner, so to speak.

Commonly, metals such as lithium, potassium, and calcium are found at the upper end of the reactivity series, indicating that they possess higher reducing power. On the other end, metals like platinum and gold are less reactive and are often found at the bottom of the series. By knowing the position of a metal on the reactivity series, you can predict its behavior in single replacement reactions.

Chemical Reactivity

Chemical reactivity refers to the tendency of a substance to engage in chemical reactions. It represents a substance's willingness to change its chemical structure by gaining or losing electrons or by breaking and forming chemical bonds.

The concept of chemical reactivity is pivotal to understanding how and why certain chemical reactions occur. Elements or compounds with high chemical reactivity are often involved in reactions that are fast and exothermic, which means they release energy. On the flip side, elements with low reactivity may react very slowly or require specific conditions to react at all.

In the case of our exercise, nickel's lower reactivity compared to metal X signifies that it has a weaker tendency to maintain its bond with sulphate. As a result, it is easily 'persuaded' to relinquish its place. This underpins why reactivity and knowledge of reducing power is so crucial in predicting the outcomes of chemical reactions, including single replacement reactions like the one involving our mysterious metal X.