The density of ethanol can be calculated using a known value or determined experimentally.
Theoretical Density
Ethanol has a known density of 0.7893 g/cm³ at 20 °C. This is a common reference value.
Experimental Density Determination
When the theoretical value isn't sufficient or if dealing with an ethanol mixture, experimental methods are necessary. The primary method uses a pyknometer. Here’s the process:
Using a Pyknometer
A pyknometer, a glass vial with a precisely known volume, is used to determine density experimentally. This method requires precise measurements.
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Preparation:
- Ensure the pyknometer is clean and dry.
- Record the empty weight of the pyknometer.
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Filling:
- Fill the pyknometer completely with the ethanol sample.
- Ensure there are no air bubbles.
- The pyknometer should be thermostatted to maintain a constant temperature (like 20°C), as density varies with temperature.
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Weighing:
- Record the weight of the pyknometer filled with ethanol.
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Calculation:
- Subtract the weight of the empty pyknometer from the weight of the filled pyknometer. This gives you the weight of the ethanol.
- Since the pyknometer has a fixed, known volume, density can be calculated using the following formula:
Density = Mass (of ethanol) / Volume (of the pyknometer)
Density Variations
- Temperature Dependence: The reference highlights that density is temperature-dependent. Therefore, accurate temperature control is essential during measurements.
- Mixtures: If the ethanol is not pure, the density will vary. Experimental measurements are necessary in such cases.
