U4-3-1 - Melting and Boiling Point Analysis

Question 1

What type of melting point range will be seen for a pure substance? (2)

Answer 1

Sharp melting point and same as literature value

Sharp = melts over a 2 °C range or less

Question 2

What type of melting point range will be seen for an impure substance? (2)

Answer 2

Broad melting point, and lower than literature value.

Question 3

Why do impure substances have lower melting points?

Answer 3

Weaker intermolecular forces (due to presence of impurities)

Question 4

Mixed melting point analysis of sample X:

1. Mix sample X with a ________________.
2. If both are the same, melting point is the same as that of the pure substance.
3. If both are different, the melting point range will be broader.

Answer 4

Mixed melting point analysis of sample X:

1. Mix sample X with a pure sample of the same substance.
2. If both are the same, melting point is the same as that of the pure substance.
3. If both are different, the melting point will be much lower.

Question 5

Mixed melting point analysis of sample X:

1. Mix sample X with a pure sample of the same substance.
2. If both are the same, melting point is ___________.
3. If both are different, the melting point range will be broader.

Answer 5

Mixed melting point analysis of sample X:

1. Mix sample X with a pure sample of the same substance.
2. If both are the same, melting point is the same as that of the pure substance.
3. If both are different, the melting point will be much lower.

Question 6

Mixed melting point analysis of sample X:

1. Mix sample X with a pure sample of the same substance.
2. If both are the same, melting point is the same as that of the pure substance.
3. If both are different, _________.

Answer 6

Mixed melting point analysis of sample X:

1. Mix sample X with a pure sample of the same substance.
2. If both are the same, melting point is the same as that of the pure substance.
3. If both are different, the melting point will be much lower.

Question 7

How can boiling point be measured?

Answer 7

Using a distillation apparatus