Describe a pycnometer.

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Detailed Solution

A pycnometer is a small, precisely calibrated volume flask with a tight stoppered capillary used to measure the density (relative density) of liquids and fine solids.

Construction: It is usually a glass bottle (typically 10–50 mL) with a ground-glass stopper that has a narrow capillary hole. When the stopper is inserted, excess liquid escapes through the capillary so the flask holds an exact, reproducible volume at a set temperature (often 20 °C).

Step	Measurement	Purpose
1. Clean, dry, weigh	Mass = m₀	Empty pycnometer mass
2. Fill with liquid, insert stopper, wipe overflow	Mass = m₁	Pycnometer + liquid at temperature T
3. Optionally repeat with water	Mass = m₂	Reference for specific gravity

Formulas: Density of liquid ρ = (m₁ - m₀)/V, where V is the calibrated volume. Relative density (specific gravity) can be found by comparing masses with water at the same temperature.

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