Free Anomalous Behaviour of Water MCQs with Answers

1. Ice is less dense than liquid water because in ice each water molecule

• A. loses one of its hydrogen atoms
• B. is hydrogen bonded to four others in an open tetrahedral arrangement
• C. moves faster than in the liquid
• D. is compressed closer to its neighbours

Explanation: Every molecule uses its two hydrogens and its two lone pairs, so a rigid open cage with large empty spaces is formed, and this occupies more volume than the same molecules jostling in the liquid. Water is therefore anomalous in expanding on freezing, which is why pipes burst in winter and why ice floats. Almost every other substance contracts as it solidifies.

2. Water has its maximum density at

• A. 0 degrees Celsius
• B. 100 degrees Celsius
• C. 4 degrees Celsius
• D. minus 4 degrees Celsius

Explanation: Cooling water from room temperature increases density as normal, but below 4 degrees the open hydrogen bonded structure begins to form and the density falls again, so the maximum occurs at 4 degrees. This is why the bottom of a deep lake stays at about 4 degrees while ice forms at the surface, allowing aquatic life to survive the winter. At 0 degrees water is already less dense than at 4.

3. Water has an unusually high specific heat capacity because

• A. it is a very light molecule
• B. it is a good electrical conductor
• C. a large amount of energy is used breaking hydrogen bonds before the temperature rises
• D. it has a low boiling point

Explanation: Much of the heat supplied goes into breaking hydrogen bonds rather than into increasing the kinetic energy of the molecules, so the temperature rise per joule added is small. This makes water an excellent coolant in car radiators and gives coastal areas milder climates than inland regions. Its high latent heat of vaporisation has the same underlying cause.