Chemistry 29a M. Walker

NOTES ON EXPERIMENT 2

Melting point is a useful test for both purity and identity.

If a sample contains soluble impurities, then its melting range will be lower and over a wider range.

If a sample’s identity is required, you mix the sample with a pure sample of what you think it is, then it will melt over the same range as the pure sample, if it is the same substance..

Note that the start of the melting range is the point where the first drop of liquid is seen, and the end of the range is where the last crystal melts. Always report a range, not just a single point.

You should use 2-3mm of sample, and no more than 2 ^cC per minute when doing a slow measurement. You can start from 20 ^oC below the expected MP.

Repeat the test until you get two consistent results (see TA) which fall within a 3 degree range (or less).

You will need to do a fast run (to find the rough MP) then a slow run to get the exact MP.

The unknowns are from the following (temperatures are in ^oC):

Benzophenone MP 49-51

Naphthalene MP 80-82

1-Naphthol MP 96-97

o-Toluic acid MP 103-105

Acetanilide MP 113-114

Benzoic acid MP 121-122

Urea MP 132-133

Salicylic acid MP 159-160

Sulfanilamide MP 165-166

Succinic acid MP 184-185

p-Terphenyl MP 210-211

Assigned Problems from chapter 4: 2, 3, 5, 9.

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