American Chemical Society (ACS) Laboratory Safety Practice Test

Which chemical is known to be water-reactive?

1. Metallic Sodium

2. Sodium Bicarbonate

3. Calcium Carbonate

4. Potassium Chloride

The correct answer is: Metallic Sodium

Metallic sodium is known to be a water-reactive chemical. When sodium comes into contact with water, it undergoes an exothermic reaction, producing sodium hydroxide and hydrogen gas. This reaction can be quite vigorous and can lead to the ignition of hydrogen, presenting a significant safety hazard in laboratory environments. Sodium bicarbonate, calcium carbonate, and potassium chloride do not exhibit the same reactive behavior with water. Sodium bicarbonate undergoes negligible reactions, primarily serving as a buffer and mild alkali. Calcium carbonate generally reacts with strong acids rather than with water itself, and potassium chloride is highly soluble in water but remains inert in terms of reactivity. Thus, metallic sodium is distinct in its immediate and energetic response to water, making it the correct choice in this context.