At what temperature is the density of water equal to 1 g/mL?

At what temperature is the density of water equal to 1 g/mL?

• A. 0°C
• B. 4°C
• C. 25°C
• D. -10°C

Answer: (B)

Water’s density changes with temperature because of how hydrogen bonds arrange the molecules. As water cools from higher temperatures, it packs more efficiently and reaches a maximum density close to 4°C. At this point the molecules are as tightly packed as they can be in the liquid state, giving about 1 g/mL. If you cool further below 4°C, the hydrogen-bond network reorganizes into a more open structure, causing the liquid to expand slightly and its density to decrease. At the freezing point the liquid becomes ice, which is even less dense than liquid water. Among the given temperatures, the density is effectively 1 g/mL at about 4°C, which is why that temperature is the correct answer.

Water’s density changes with temperature because of how hydrogen bonds arrange the molecules. As water cools from higher temperatures, it packs more efficiently and reaches a maximum density close to 4°C. At this point the molecules are as tightly packed as they can be in the liquid state, giving about 1 g/mL. If you cool further below 4°C, the hydrogen-bond network reorganizes into a more open structure, causing the liquid to expand slightly and its density to decrease. At the freezing point the liquid becomes ice, which is even less dense than liquid water. Among the given temperatures, the density is effectively 1 g/mL at about 4°C, which is why that temperature is the correct answer.