Lab 1 part 3

Question 1

What does melting point help us to determine?

Answer 1

a. Purity of an organic compound
b. Identify the organic compound

Question 2

Pure crystalline compounds have ____melting points.

Answer 2

sharp

Question 3

Melting points are always reported as a

Answer 3

range.

For
example, the melting point of benzoic acid is 121-1220 C

Question 4

The melting point of benzoic acid is 121-122 C. What does the first number indicate? What does the second number indicate?

Answer 4

• The first number indicates the temperature at
  which the sample begins to melt
• the second number tells you when the sample has melted completely.

Question 5

What does a narrow range mean when thinking about the compound?

Answer 5

The narrower the range, the purer the compound

Question 6

Would a range of 5 degrees c be considered pure or impure

Answer 6

A range of 50 C would indicate the compound to be impure.

Question 7

How do we use melting point to identify an organic compound?

Answer 7

We determine the melting point of the
given compound and from the literature figure out what the compound is. If two compounds are same, mixing them will not cause any change in the melting point. If two compounds are different, mixing them will cause a lowering of melting point. One serves as an impurity in the other and lowers the melting
point. The range will also be broader than either substance alone.

Question 8

If two compounds are same,
will mixing them cause any changes

Answer 8

No changes in the melting point

Question 9

. If two compounds are different, will mixing them cause a change

Answer 9

yes, cause a lowering of melting point.

Question 10

When two compouds are different, one serves as an___, and _____the melting point. The range will be_____ than either substance alone.

Answer 10

impurity
lowers
broader

Question 11

When dealing with mixtures, what is the procedure?

Answer 11

Take approximately equal amounts of the compounds for which you have already determined the melting
points and mix them thoroughly and grind them well

Question 12

How to determine identity of unknown?

Answer 12

Prepare a mixture of the compound with the compound that is most likely of
the possible choices and take the melting point of the mixture. If the melting point is the same as that of the unknown then it means that your unknown and the compound with which you mixed it are the same. If the melting point is lowered then the compound is acting as an impurity in your unknown. You need to
take another compound whose melting point is close to your unknown and determine the melting point again