Physics 2010 JAMB Past Questions - Question 13: The accurate measurement of the relative density of a substance in its powdered form is done with a beam balance and

Correct Answer

D

Explanation

The accurate measurement of the relative density of a substance in its powdered form is typically done using a laboratory instrument known as a "pycnometer" or "gas pycnometer" rather than a beam balance. A pycnometer is a specialized piece of equipment designed for this purpose. Here's how the process works:

1. Sample Preparation: Start by obtaining a sample of the powdered substance. The sample should be carefully weighed to determine its mass accurately.

2. Pycnometer Filling: The pycnometer is a glass or metal container with a known volume. It is initially weighed when empty. Next, the pycnometer is filled with a known amount of a gas, often helium or nitrogen, to a high pressure. This pressurized gas serves as the displacing medium.

3. Filling the Pycnometer: The sample of the powdered substance is carefully placed into the pycnometer, and the pycnometer is sealed to ensure no gas can escape.

4. Measurement of Pycnometer Mass: The filled pycnometer is weighed again. The mass of the pycnometer with the sample inside and the pressurized gas is determined.

5. Calculation: Using the known volume of the pycnometer and the measured mass, the relative density of the powdered substance is calculated using the following formula:

  Relative Density (RD) = (Mass of Sample + Mass of Gas) / Mass of Pycnometer - Mass of Gas

The gas in the pycnometer is pressurized and is typically at a known pressure and temperature, which is considered during the calculation. The relative density obtained through this method is an accurate measurement because it accounts for the volume of the powdered substance in a precise manner.

A beam balance, on the other hand, is typically used for measuring mass (weight) and is not the instrument of choice for determining the relative density of a substance, especially in its powdered form.