Probable Quiz Questions

Question 1

List the four forces that hold organic solids together

Answer 1

1) Ionic attraction
2) Hydrogen bonding
3) Dipole-dipole interactions
4) Van der Waals forces

Question 2

List the four forces from weakest to strongest

Answer 2

1) Van der Waals forces
2) Dipole-dipole interactions
3) Hydrogen bonding
4) Ionic attraction

Question 3

Define melting point

Answer 3

When the vapor pressures of a solid and liquid are equal

Question 4

State 2 ways that melting point is used in organic chemistry

Answer 4

1) To characterize

2) To determine the purity of compounds

Question 5

What effect do impurities have on the melting point of a solid sample? (Give 2 examples)

Answer 5

1) Lower melting point
2) Wider range of temperatures that melting point may occur at

If there are impurities in phthalic acid, as a solid it will experience a generally lower melting point that may occur within a wider range of temperatures

Question 6

Of the following compounds, which has the highest melting point?

A) CH3CH2CH3
B) CH3CH2OH
C) CH3CH2NH2
D) HOCH2CH2OH

Answer 6

D

Question 7

Why does the compound HOCH2CH2OH have a higher melting point?

Answer 7

The compound has two instances of hydrogen bonding, whereas the other compounds either have just 1 (like option B) or none at all (A and C). 2 instances of hydrogen bonding increase its melting point above the other compounds.

Question 8

What is the formula for percent recovery and what is it used for?

Answer 8

(Amount of pure solid/Amount of impure solid)x100

It is used to see how much of the original pure substance you have at the end of the experiment.

Question 9

What is the percent difference for a substance if the known 100% melting point is 230 degrees Celsius and the measured melting point is 214 degrees Celsius? JUST SHOW CALCULATION, DON’T DO IT.

Answer 9

(230-214/230)x100=% difference

Question 10

Recrystallization is an important method for purification. Explain why the choice of solvent is important.

Answer 10

The solvent must be able to dissolve the solute (“like dissolves like”), it must be nontoxic, volatile so it can be removed from the crystals, inexpensive, nonflammable, should not react with the solid, must dissolve the solute at high temperatures but not show any appreciable increase in solubility at low temperatures, the solid compound should crystallize when the hot solution is cooled to room temperature or set in an ice bath, and it must be able to dissolve the impurities very well or not at all.