Question about Experimentally Measuring Mass

[jtang03]

In an experiment that I conducted, I was instructed to measure the mass of a substance (NaCl) in it's container BEFORE measuring the mass of just the container.

Is there a logical reason behind doing it in this order rather than measuring the mass of the container FIRST AND THEN measuring the mass of the container + NaCl?

[Studiot]

The only circumstance in which you can do is is if you then to transfer the NaCl to some other container.
When you make the second measurement you are not only measuring the mass of the container you are including the mass of any residue left behind.

That way your difference of masses will truly be the amount of NACl used.

If you were going to keep the NaCl in the container you would have to do the measurement the other way round.

go well