Suppose you were calibrating a 25.0 mL volumetric flask using distilled water.

Question

Suppose you were calibrating a 25.0 mL volumetric flask using distilled water. The flask temperature was at 20 °C , and you assumed that the distilled water was as well. However, you later discover that the actual water temperature was 11 °C instead.

How is the mass of the 25.0 mL of distilled water you measured at 11 °C different from the mass of 25.0 mL of distilled water at 20 °C ?

A. It has the same mass as the water at 20 °C .

B. It is less than the mass of water at 20 °C .

C. It is greater than the mass of water at 20 °C .

If the masses are different, is the error in mass due to the temperature difference a systematic or random error?

A. It is both a systematic and random error.

B. It is neither a systematic or random error because the masses are the same.

C. It is a systematic error.

D. It is a random error.

Answer 1

Since the temperature of the water was 11ºC, the density of that water would be different from the density of water at 20ºC and thus the mass would be different. Looking up density of water at 11ºC and 20ºC, I find it to be 0.99960 g/ml and 0.99820 g/ml, respectively. Thus, the equivalent masses of 25.0 ml would be...

@11ºC 25.0 ml x 0.99960 g/ml = 24.99 g

@20ºC 25.0 ml 0.99820 g/ml = 24.96 g

So, (C) it is greater than the mass of water at 20ºC

This would be a systematic error (C) because it would lead to a predictable and consistent error