Measuring melting point

Question 1

what’s measuring the melting
point used for

Answer 1

to test for the degree of purity of a mixture

Question 2

is the sample is very pure what would the melting point be

Answer 2

it would be at the same values as quoted in data books

Question 3

what happens to the melting point if impurities are present

Answer 3

the melting point will be lowered and the sample will i’ll melting over a range of several degree celsius

Question 4

how can melting point be measured

Answer 4

in an electronic melting point machine or a practical set up where the capillary tube is strapped to a thermometer immersed in heating oil
- in both cases a small amount of the sample is put into a capillary tube .
- This tube is heated up and is heated slowly near the melting point

Question 5

how can u determine the degree of purity

Answer 5

comparing an experimentally determined melting point value with one quoted in a data source

Question 6

why might an error occur sometimes

Answer 6

if the temperature on the thermometer is not the same as the temperature in the actual sample tube

Question 7

EQ : State two observations during this melting point determination , that would indicate that the sample is not pure (2)

Answer 7

• Melts over a range of temperatures
• Below the true melting point

Question 8

EQ : You are provided with a small sample of pure aspirin in a melting point tube . Describe briefly how you would determine an accurate value for the melting point of aspirin (2)

Answer 8

• Heat melting point tube in an oil bath / melting point apparatus
• Slowly near the melting point

Question 9

EQ : Suggest why a pure sample of aspirin may sometimes appear to melt at a temperature different from 135 degrees (1)

Answer 9

Temperature on thermometer not the same as sample

Question 10

EQ : describe briefly how you could measure the melting point of aspirin (2)

Answer 10

• sample in capillary tube / melting point tube
• heat in melting point apparatus

Question 11

EQ : outline how you would carry out a simple lab process to show that the recrystallised product is a pure sample of N-phenylethanamide (3)

Answer 11

measure melting point
use melting point apparatus or oil bath
sharp melting point / melting point matches data source value