Which statement about the small pycnometer is true?

• A. When using the small pycnometer, the fixture is weighed together with the pycnometer.
• B. The fixture is weighed separately from the pycnometer.
• C. The small pycnometer is never used in this procedure.
• D. The fixture is weighed after the pycnometer is emptied.

Answer: (A)

In this method, you’re determining the density of a fixture using a small pycnometer, so the weight that matters is the combined mass of the fixture and the pycnometer in the same state. Weighing the fixture together with the pycnometer captures the true mass of the system as it sits in the liquid (or in the configuration used for the measurement), which is essential for correctly calculating volume and buoyancy. If you tried to weigh them separately, you’d introduce additional steps and potential errors because the buoyant forces and the reference masses wouldn’t align with the condition used in the calculations. The small pycnometer is indeed used in this procedure, and weighing after the pycnometer is emptied would not yield the required combined mass for the calculation.