International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

How should Group 1 elements be stored to prevent reaction?

1. In air

2. Under water

3. Under oil

4. In a vacuum

The correct answer is: Under oil

Group 1 elements, also known as alkali metals, are highly reactive, especially with moisture and oxygen in the air. Their reactivity increases down the group, making them susceptible to vigorous reactions with these substances. To prevent unwanted reactions, alkali metals are best stored under oil. The oil creates an effective barrier that prevents contact with both air and moisture, which could lead to oxidation or other chemical reactions. Additionally, storage under oil helps to minimize the risk of the metals catching fire, as some alkali metals can ignite spontaneously in the presence of water or moisture. Storing these elements in air would expose them to oxygen and moisture, leading to rapid corrosion or even violent reactions. Storing them under water is dangerous because it would lead to highly exothermic reactions, producing hydrogen gas that could ignite. A vacuum storage is unnecessary and impractical for these metals when oil serves as a safer and more effective solution to prevent reactions.