Why must you measure the mass of an object oce it has cooled and not when it is hot?

Question

This question was on my chemistry homework and I have no idea what the answer is. I couldn't find it in my textbook, on Google, and my mom didn't know. I don't want to not answer it because I think my chemistry teacher might take points off. This could be a hint- hot air and cold air make wind. I heard my teacher telling this to another student, but it doesn't help me. She could have been referring to a different question, but it doesn't really make sense for any of the other ones. Also, note it says MASS, not weight or volume.

Answer 1

  The mass won't change but at least you will be able to pick it up.

Answer 2

The mass won't change by any measurable amount due to heating.  The volume will.  So any measurements of mass at temperatures you could achieve in the average laboratory would be as accurate as the balance.  But I'd think that you're likely to burn yourself if you pick up something that is hot.  Other than that, there's no reason you can't measure the mass of a hot object.  Unless your balance can be damaged by the heat, or if it's heat sensitive.  This could actually be the case with some electronic balances.  The plates rest on metal that can expand and effect the measurement.  But the tare function would essentially eliminate these issues.

Answer 3

Well, I'll answer this as if you were weighing it on an analytical balance.  A heated object will create its own convection currents that will distort the mass measurements of an instrument.  This is why you let the object reach room temperature first, then weigh it.  This is also why ''accurate'' balances usually have a box around the instrument to prevent air currents from messing up readings.

Hope this helps.

Answer 4

When things are hot they expand. If you measure something while it's hot, the measurement will be different from what it should be.