Why are knowing melting and boiling points important?

Question

Why are knowing melting and boiling points important?

Answer 1

Just think practical. For instance when you want to use heat shrink tubing to hold things together or secure your speaker wires you need to know the melting point so you know how hot to make it so it will shrink. If you are working on your car and are putting things under the hood or close to the engine you would need to have an adhesive or tape that can withstand the heat. Especially if you are doing exhaust work. For my dryer downstairs I had to patch the vent pipe with some tape and if I would have used masking tape it would have caught on fire, so I used car muffler tape because it won't melt. Your other answers were good too. How about making yourself some french fries? You don't want the oil to boil right? You would get hurt. So you have to keep it below the boiling point.

Answer 2

Melting points are important because they indicate compound purity.  If you synthesize a compound and measure its melting point and the melting point is well-defined (i.e., the compounds melts over a very small temperature range) and the temperature agrees with values reported in the literature (if those are available), then it is a strong piece of evidence that the sample is relatively pure.  Boiling points are important for the same reason, a well-defined boiling point indicates purity.

The general term to look for is colligative properties, specifically melting point depression, boiling point elevation, or Raoult's Law for mixtures of liquids.  

There are other reasons why these properties are useful, assessing vapor pressures is one application (for example, vapor pressures are required if you want to model how smog forms in the atmosphere), but originally they were used as indicators of purity.

Answer 3

Because chemists, for example,  need to know at what point a substance turns to a gas(boiling point) and a liquid(melting point). This is important because some reactions require sudstances in an alternative state, and its also important for knowing the different stages in a reaction!

Answer 4

So they know what temperature antifreeze needs to work at and how to turn off a kettle  - among others.