[sasuke07]

1. What voltage should be used when a melting point determination is performed on caffeine?

2. Pure 4-carboxybenzaldehyde (mp 245°C) is a white crystalline solid material at room temperature. Which of the melting
points is(are) consistent with a sample of caffeine containing a small quantity of 4-carboxybenzaldehyde? Select ( ) all that
apply.
212°C  215-227°C  236-240°C  238°C
 239-243°C  240°C  245°C  None of these melting
points

Thanks.

[discodermolide]

Well I don't know about the voltage, how about 10 Megavolts?
But what happens ti the MPt. of a compound when an impurity is added?

[sasuke07]

wouldn't the melting point get broader?, but still not sure which ones to select because it could be more than 1

[discodermolide]

Think about what happens to the MPt. of water when you add salt to it, does it go up or down?

[Babcock_Hall]

Sometimes the melting range of an impure substance changes in another way (besides being lower on average than a pure substance).  That is why it is best to record a range, as opposed to a point.