Question

The percentage of water in an unknown hydrated salt is to bedetermined by weighing a sample of the salt, heating it to driveoff water, cooling it to room temperature, and re-weighing. Whichprocedural mistake would result in determining a percentage ofwater that is too low?
Procedural Mistakes

I. heating the sample in aclosed, rather than an open, container
II. re-weighing thesample before it has cooled to room temperature

A. I only
B. II only
C. both I andII
D. neither I norII

Answer 1

Answer:

B

Explanation:

If the sample is reweighed after it is removed from the furnace without being cooled to room temperature, its percentage water content will be too low as there would be almost no water if crystalization at such high temperature. However, when it is cooled to room temperature, the actual percentage of water contained in the sample can be accurately determined by weighing.