Measurement (chemistry)?

Question

1. How to determine the boiling by observation?

2. why it is not allowed to blow the rest of the water from the pipet?

Answer 1

1. The water bubbles and evaporates when it's boiling.

2. The pipette is calibrated so that there is an allowance made for the amount that remains in when you empty it. If you blow the rest out, you will have delivered a greater amount than stated by the pipette's scale.

Answer 2

1. The definition of boiling is when vapor pressure = atmospheric pressure.  You can observe this by seeing large bubbles form in the boiling liquid.

2.  You should never use your mouth on a pipet.  First, you don't know where it's been (as your mother would say).  Second, if you sucked instead of blew, you could get chemicals in your mouth.  Third, you might send some spit down the tube.  This could contaminate whatever it is your working on.  If you're not sure of this, check out a balloon that you blew up.  If you pop it, you'll notice the inside of it is wet, Yuck.