Organic Chemistry Lab Midterm

Question 1

Define eutectic point

Answer 1

The lowest point where the mixture has a very narrow range (in terms of melting point graph). Also the point at which two solids of liquid solution are at equilibrium (with regard to two solids in liquid solution).

Question 2

3 applications that utilize the melting point of measurements

Answer 2

1. Identify unknowns
2. Evaluate purity
3. Calibrate machines

Question 3

Explain why it’s important to calibrate the thermometer and the melting point apparatus

Answer 3

It’s important since inaccurate readings can mess up an experiment or misidentify the compounds so that when using these devices one can get accurate melting point by eliminating system errors

Question 4

Why does NaCl melt at a much higher temperature than glucose

Answer 4

Ionic bonds are harder to change the state of

Question 5

How can you tell if a compound is pure or not from its melting point?

Answer 5

Impurities lower the melting point and range of the compound

Question 6

Melting point of biphenyl

Answer 6

69-70 C

Question 7

Melting point of mandelic acid

Answer 7

120-121 C

Question 8

Melting point of benzoic acid

Answer 8

122-123 C

Question 9

Melting point of malic acid

Answer 9

131-132 C

Question 10

Melting point of cinnamic acid and urea

Answer 10

132-133 C

Question 11

Melting point of sebacic acid

Answer 11

133-135 C

Question 12

Melting point of benzoin

Answer 12

135-136 C

Question 13

Melting point of malic acid

Answer 13

137-139 C

Question 14

Ethanol is a good solvent for …

Answer 14

Nonpolar compounds

Question 15

Water is a good solvent because

Answer 15

It is polar and therefore dissolves polar substances well

Question 16

How are benzoic crystals shaped?

Answer 16

Flat, white crystals

Question 17

Oiling out occurs when …

Answer 17

Coalescence continues to complete separation (breakdown) of the emulsion, which causes an oily substance to emerge.

Question 18

Boiling chips are often used when a solvent is heated to a boil because …

Answer 18

It helps the substance boil evenly and prevents burping, using more than one can cause loss of crystals.

Question 19

Why is it sometimes necessary to filter a hot solution?

Answer 19

This helps filter out any insoluble impurities.

Question 20

Is boiling the recrystallization solution for a very long time necessary? Does this impact the outcome?

Answer 20

It is not necessary, and it can affect the composition of the substance.

Question 21

Define boiling point

Answer 21

The temperature at which a liquid changes to a gas

Question 22

Why should the side arm be placed deep in the receiving vial?

Answer 22

To prevent as much loss of the product as possible via escaping as a gas

Question 23

Why is experimental boiling point lower than literature?

Answer 23

This is due to a pressure difference because we are at a higher elevation. Lower elevation (greater atmospheric pressure) = higher boiling point.

Question 24

Single most important variable that contributes to an effective separation of liquids by distillation

Answer 24

Distillation rate

Question 25

Explain why during distillation the first few drops are cloudy

Answer 25

First drops wash water off the condenser and appear cloudy

Question 26

Charcoal is used to ...

Answer 26

Remove color

Question 27

Which is more polar; benzoic acid or acetanilide?

Answer 27

Benzoic acid

Question 28

Because benzoic acid is more polar we have to use NaOH

Answer 28

Because it is a more polar solvent

Question 29

Benzoic acid is more acidic because

Answer 29

The pKa value is lower

Question 30

Why are drying agents used?

Answer 30

They remove trace amounts of water that are dissolved in an organic solvent

Question 31

Dilution equation

Answer 31

M1V1=M2V2

Question 32

Why do you not use excess drying reagent?

Answer 32

It results in loss of desired product and generates more chemical waste

Question 33

If the density of the organic layer is not known, explain how you can tell which layer is aqueous and which is organic.

Answer 33

Funnel a drop of water down the tube and observe which layer it goes to.

Question 34

What does cloudiness in the organic layer indicate in extraction, and how can it be removed?

Answer 34

It indicates presence of small amounts of water, and it's removed by adding a drying agent.

Question 35

Criteria for a good extraction solvent

Answer 35

1. Ability to selectively dissolve the compound 2. Must not react with the compound 3. Must be immiscible