Pre Lab Experiment 4: Melting Point

Question 1

What 2 compounds are used these labs?

Answer 1

Cinnamic Acid and Benzoin

Question 2

Melting Point is the Primary index of what?

Answer 2

M.P. is the primary index of purity for a crystalline solid

Question 3

What is T1 and T2 refer to?

Answer 3

For a Melting Point Range:

1) T1 is the temp that the first liquid appears
2) T2 is the temp that all of the crystals turn into liquid

Question 4

How do we use M.P. to assess purity?

Answer 4

1) Higher Purity –> Higher M.P. + Narrow M.P. Range

2) Lower Purity –> Lower M.P. + Broad M.P. Range

Question 5

Why did we use Cinnamic acid and Benzocaine in this experiment? What is a mixed melting point?

Answer 5

These 2 have almost identical melting points. We used these 2 to investigate the impact of impurities on melting point. Despite having these 2 having the same melting point, when mixed together in different portions, they had much lower melting point range.

Question 6

What do all M.P. apparatuses have?

Answer 6

1) Magnifying glass
2) Sample holder
3) Cooling block, blower
4) Thermometer
5) Calibration equation

Question 7

What equipment do we use to prepare samples for Fischer-John and Mel-Temp?

Answer 7

1) Microcover slides - Fischer-Johns
2) Capillary tubes - Mel-Temp
- Use drop tube to pack crystals in capillary tubes

Question 8

What an efficient way to measure M.P. for an known and unknown sample?

Answer 8

1) If Known sample
- Heat to 15-20 degrees below known M.P. quickly with high heat
- Decrease to 2 degrees per minute over M.P. range
2) If Unknown sample
- Use a sacrifice sample and heat as fast as possible until it melts (Will be lag)
- Heat second sample 15-20 degrees below that intitial temp and decrease to 2 degrees per minute over M.P. range