How can you distinguish between water and ethanol?

• A. Use cobalt chloride paper, it turns from pink to blue with water, but there will be no change with ethanol.
• B. Taste them to tell the difference.
• C. Look at boiling points to distinguish.
• D. Mix with litmus and observe color change.

Answer: (A)

The test relies on how cobalt chloride paper responds to water molecules. Cobalt(II) chloride on the paper changes color when it forms a hydrated complex with water. In this scenario, the paper starts pink and turns blue when water is present, showing that water is there. Ethanol, while it can mix with water, does not hydrate the cobalt chloride in the same way, so the paper does not undergo the same color change. That makes cobalt chloride paper a simple and reliable way to tell water from ethanol, since only water produces the distinct color change.

Tasting is unsafe and unreliable. Looking at boiling points would require heating and more equipment, and mixing with litmus won’t reliably differentiate since both liquids are neutral and don’t cause a color change in standard litmus tests.