Experiment#2: Melting Point

Question 1

The temperature at which a solid and liquid co-exist in equilibrium.

Answer 1

Melting Point

Question 2

A melting point is also equal to a _____ point of a solid.

Answer 2

freezing point

Question 3

Occurs when the energy supplied by heating is just sufficient enough to overcome these forces so that the molecules become mobile.

Answer 3

Melting

Question 4

PROCESS OF MELTING POINT [MP]
Enumerate the 2 purposes of determining an MP

Answer 4

• Identify/Identification of Substances
• To check the purity of solid organic compounds.

Question 5

PROCESS OF MELTING POINT [MP]
Enumerate the 4 Factors affecting MP

Answer 5

• Large Pressure Difference
• Molecular Structures
• IMFA
• Impurities (added during post-lab discussion)

Question 6

PROCESS OF MELTING POINT [MP]
What are the 3 different apparatus one can use to determine a compound’s melting point?

Answer 6

• Fisher-Johns
• Kofler
• Thiele Tube

Question 7

TRUE or FALSE | PROCESS OF MELTING POINT [MP]
To close off a capillary tube, one must insert the entire half end of the tube into the burner whilst rotating.

Answer 7

FALSE. Only the end of the tube touches the flame. There is absolutely no need to rotate.

Question 8

TRUE or FALSE | PROCESS OF MELTING POINT [MP]
To signal that the capillary tube has closed, a yellow sodium flame will appear.

Answer 8

TRUE

Question 9

PROCESS OF MELTING POINT [MP]
In what piece of laboratory equipment do we drop the loaded capillary tube in to ensure that it packs together at the closed end?

Answer 9

Long Glass Tubing

Question 10

PROCESS OF MELTING POINT [MP]
You go through the two trials needed during a melting point experiment, and deduce the following:

In Trial 1, the substance melts at 212 °C.
In Trial 2, the substance melts at 190 °C.

Using the formula to determine a compound’s average melting point, what then would the average melting point of your unknown substance be - based on the 2 trials?

Answer 10

201 °C.

[AveMP Formula: (Trial 1 + Trial 2)/2]
= (212+190)/2 = 402/2 = 201.

Question 11

INTERMOLECULAR FORCES OF ATTRACTION [IMFA]
If a compound has strong IMFA, its MP therefore is ____.

Answer 11

HIGH | The stronger the IMFA, the higher the MP

Question 12

INTERMOLECULAR FORCES OF ATTRACTION [IMFA]
In determining and comparing the melting point of two compounds, if their molecular weight is similar to each other, then the ____ of a compound dominates.

A) Polarity
B) IMFA
C) Pressure Difference
D) Structure

Answer 12

A) Polarity

Question 13

INTERMOLECULAR FORCES OF ATTRACTION [IMFA]
In determining and comparing the melting point of two compounds, if their molecular weight is different from each other, then the ____ of a compound dominates.

A) Polarity
B) IMFA
C) Pressure Difference
D) Structure

Answer 13

B) IMFA

Question 14

TRUE or FALSE | MELTING POINT [MP]
Symmetry and compactness of a molecule results in a lower MP because it’s easier to break down.

Answer 14

FALSE. Symmetrical and more compacted molecules result in a HIGHER MP because it requires a larger amount of energy to break its molecular structure.

Question 15

TRUE or FALSE | IMPURITIES

1) The presence of impurities increases a compound’s melting point.

2) The presence of impurities increases a compound’s MP range.

3) The presence of impurities weakens IMFA because it causes defects in the molecule’s structures.

Answer 15

1) FALSE it lowers it.
2) TRUE
3) TRUE