Question

Which metal does not give the following reaction \(\mathbf{M}+\) water or steam \(\longrightarrow\) oxide \(+\mathrm{H}_{2} \uparrow\) (1) Iron (2) Sodium (3) Mercury (4) Magnesium

Short answer

Mercury

Step-by-step solution

Understand the Reaction

Metals react with water or steam to form metal oxides and release hydrogen gas. The general reaction can be written as: \[ \text{Metal (M)} + \text{H}_2\text{O (l)} \longrightarrow \text{Metal oxide} + \text{H}_2 \uparrow \]

Iron

Iron reacts with steam to form iron oxide and hydrogen gas: \[ 3\text{Fe} + 4\text{H}_2\text{O} \longrightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2 \]

Sodium

Sodium reacts vigorously with water to form sodium hydroxide and hydrogen gas: \[ 2\text{Na} + 2\text{H}_2\text{O} \longrightarrow 2\text{NaOH} + \text{H}_2 \]

Mercury

Mercury does not react with water or steam to form an oxide and hydrogen gas. Mercury's lack of reactivity is due to its position in the reactivity series of metals.

Magnesium

Magnesium reacts with steam to form magnesium oxide and hydrogen gas: \[ \text{Mg} + \text{H}_2\text{O} \longrightarrow \text{MgO} + \text{H}_2 \]

Conclusion

Based on the reactions described, Iron, Sodium, and Magnesium react with water or steam to form oxides and hydrogen gas. Mercury does not.

Key concepts

metal reactivity series

The metal reactivity series is a list that ranks metals by their reactivity. This series helps us predict how metals will react with other substances, like water. In the reactivity series, metals at the top are the most reactive, while those at the bottom are the least reactive.
Mercury is at the lower end of this series, meaning it is less likely to react with other substances, including water.
Contrast this with metals like sodium, which is very high on the reactivity series and reacts vigorously with water. This is why in our original exercise, mercury did not react with water or steam to form an oxide and release hydrogen gas, while metals like iron, sodium, and magnesium did.

metal-water reaction

The reaction between metals and water depends on the metal's position in the reactivity series. Metals high in the series, such as sodium, react directly with cold water. Metals lower in the series, like iron, usually require steam to react.
For example, sodium reacts quickly and vigorously with water, forming sodium hydroxide and releasing hydrogen gas: \[ 2\text{Na} + 2\text{H}_2\text{O} \longrightarrow 2\text{NaOH} + \text{H}_2 \]
Iron, which is less reactive than sodium, reacts with steam rather than cold water to form iron oxide and hydrogen gas: \[ 3\text{Fe} + 4\text{H}_2\text{O} \longrightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2 \]
On the other hand, mercury does not react with water or steam at all.

hydrogen gas release

When metals react with water or steam, one of the products is usually hydrogen gas. The release of hydrogen gas can be observed as bubbles forming in the water.
This occurs because the metal atoms lose electrons to the hydrogen ions in water (H\textsubscript{2}O), reducing them to hydrogen gas (H\textsubscript{2}).
For example, in the reaction between magnesium and steam: \[ \text{Mg} + \text{H}_2\text{O} \longrightarrow \text{MgO} + \text{H}_2 \]
Here, magnesium gives up electrons to hydrogen ions, forming magnesium oxide and releasing hydrogen gas. Understanding the production of hydrogen gas can help students grasp broader concepts in chemistry, like redox reactions and the behavior of metals.
In our exercise, since mercury is very low on the reactivity series, it does not donate electrons to hydrogen ions. Therefore, no hydrogen gas is produced.