Water density of approximately 1000 kg/m^3 – at what condition? The statement “the density of water is about 1000 kg/m^3” is most accurate under which condition?

Introduction / Context:
Texts often quote water’s density as 1000 kg/m^3, but this is temperature dependent. Recognizing the correct reference condition avoids small but important errors in buoyancy, hydrometry, and calibration of volumetric glassware.

Given Data / Assumptions:

• Fresh water (not saline), near 1 atm pressure.
• Density varies primarily with temperature over typical laboratory ranges.
• Compressibility effects due to pressure are minor at near-atmospheric conditions.

Concept / Approach:

Pure water reaches its maximum density near 4°C, about 999.97 kg/m^3, commonly rounded to 1000 kg/m^3. At higher temperatures (e.g., 20°C), density is lower (~998 kg/m^3), and at 0°C it is also lower (~999.8 kg/m^3), with small pressure dependencies around atmospheric pressure.

Step-by-Step Solution:

Verification / Alternative check:

Density tables used for hydrometers and volumetric calibration confirm the maximum near 4°C, with deviations of about 0.2% across typical room temperatures.

Why Other Options Are Wrong:

(a) Pressure specification alone is insufficient; temperature matters. (c) “Any temperature” is incorrect because density changes with temperature. (d) Not all conditions are equally accurate. (e) Vacuum conditions are irrelevant to liquid water’s density at standard states.

Common Pitfalls:

Confusing density with specific weight (≈9.81 kN/m^3); assuming salinity has no effect (seawater is denser than pure water).

Final Answer:

at approximately 4°C (fresh water, near standard pressure)