Water Density Maximum: Understanding the Anomaly

Density is defined as mass per unit volume. For most substances, density increases as temperature decreases. However, liquid water exhibits unusual behavior, known as the density anomaly. This means its density does not continuously increase as it cools down.

The Science Behind Water's Maximum Density

Water reaches its maximum density at approximately 4 degrees Celsius (4°C). Below this temperature, as water cools further towards its freezing point (0°C), its density actually starts to decrease.

This phenomenon is due to the hydrogen bonding between water molecules. As water cools from higher temperatures, the molecules pack closer together. However, as it approaches 0°C, the hydrogen bonds start to form a crystalline lattice structure, similar to ice, which requires more space between molecules. This open structure causes the density to decrease.

To convert Celsius to Kelvin (K), we use the formula:
\(T_{\text{K}} = T_{\text{°C}} + 273.15\)
So, 4°C is equivalent to:
\(T_{\text{K}} = 4 + 273.15 = 277.15 \text{ K}\)
Therefore, the temperature for maximum density is approximately 277 K.

Analyzing the Options for Maximum Water Density

Let's examine the given options:

• 299 K: This is approximately 26°C, well above the temperature of maximum density.
• 277 K: This is approximately 4°C (277.15 K), which is the temperature where water density is maximum.
• 285 K: This is approximately 12°C, also above the temperature of maximum density.
• 373 K: This is 100°C, the boiling point of water at standard pressure. Water is much less dense at this temperature compared to its density at 4°C.

Based on the scientific understanding of water's properties, liquid water shows maximum density at approximately 277 K.