Question

Which of the following metals can react with water? (a) \(\mathrm{Au},(\mathrm{b}) \mathrm{Li},(\mathrm{c}) \mathrm{Hg},(\mathrm{d}) \mathrm{Ca},(\mathrm{e}) \mathrm{Pt}\)

Short answer

The metals that can react with water are Lithium (Li) and Calcium (Ca)

Step-by-step solution

Identifying Reactive Metals

From the options given, we identify two metals - Lithium (Li) and Calcium (Ca) - to be among the most reactive. Reactive metals tend to readily react with water.

Checking for Non-Reactive Metals

We notice three metals - Gold (Au), Mercury (Hg) and Platinum (Pt). These are considered to be among the least reactive metals and thus do not react with water.

Key concepts

Lithium

Lithium is one of the lightest metals and is highly reactive, especially with oxygen and water. As an alkali metal, lithium is located in Group 1 of the periodic table. This group is known for having very reactive elements. When lithium comes in contact with water, it reacts vigorously, although not as explosively as some of its relatives such as sodium and potassium.

Here's how the reaction occurs:

• Lithium reacts with water to form lithium hydroxide (\[\ce{LiOH}\]) and hydrogen gas (\[\ce{H2}\]).
• This reaction can be represented by the equation: \[\ce{2Li + 2H2O -> 2LiOH + H2}\]
• Hydrogen gas is flammable, which can cause popping or fizzing as it escapes.

Understanding lithium's reactivity helps explain its careful handling in lab settings to prevent unwanted reactions.

Calcium

Calcium is an alkaline earth metal, situated in Group 2 of the periodic table. It's less reactive than similar alkali metals, but still reacts noticeably with water.

When calcium comes into contact with water:

• It forms calcium hydroxide (\[\ce{Ca(OH)2}\]) and hydrogen gas (\[\ce{H2}\]).
• The chemical reaction can be expressed as: \[\ce{Ca + 2H2O -> Ca(OH)2 + H2}\]
• This interaction leads to the release of hydrogen gas, which might cause the solution to bubble initially.
• The resulting calcium hydroxide can be seen as a milky suspension in the water.

The moderate reactivity of calcium is significant in understanding its role in various chemical and biological processes.

Water Reaction

When certain metals react with water, they transform the water molecules into a hydroxide and release hydrogen gas. The reactivity of metals with water is largely determined by the position of the metal in the periodic table.

Let's consider the factors influencing these reactions:

• Metals in Group 1 (alkali metals) and Group 2 (alkaline earth metals) are more likely to react with water.
• The reaction typically involves the metal displacing hydrogen from water, forming a metal hydroxide and liberating hydrogen gas.
• Some metals, like gold (Au), mercury (Hg), and platinum (Pt), are considered noble metals, and do not react with water due to their low reactivity levels.

These reactions are critical for understanding both natural phenomena and industrial applications, where controlling reactivity is essential.