[glaizy]

how fast do you heat a sample when determining a melting point?
 

i'm confused if the answer is the time or something?

[discodermolide]

how fast do you heat a sample when determining a melting point?
 

i'm confused if the answer is the time or something?

Do a rough determination of the MPt.
Then heat relatively fast to around 10-15°C below the MPt. Then heat slowly around 1 degree per minute or slower until it melts.

[glaizy]

what is the affect of impurity of the boiling point of the substance?
increase, right?

[orgopete]

Good question. I preferred using a Thomas-Hoover melting point apparatus. They have the highest wattage heater. I always made two melting point tubes. Put one in and do it as maximum heat. Watch the temperature when it melts, immediately turn off the heat. It will overshoot. Wait until the temp falls below or in the range of what it was when you sample melted. If it melts when you put in your second sample, quick, make up a third mp tube. Do melting point as normal, or slow or fast as you the purity of your sample suggests. (If I know it isn't pure anyway, I am not going to wait around to do a slow determination of a wide mp range.)

For me, the only thing that I liked about a melting point is as a poor man's test of purity. I wouldn't worry about the actual melting point. This isn't pre NMR or IR. If it melted over about two degrees and I could do my entire melting point determination in five minutes or less. I was happy. You can tell if it softens (a little even), but doesn't melt all at once. That is what you want to know.