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Organic Chemistry Lab > Organic Chemistry Lab Midterm > Flashcards

Organic Chemistry Lab Midterm Flashcards

1
Q

Define eutectic point

A

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).

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2
Q

3 applications that utilize the melting point of measurements

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

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

A

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

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4
Q

Why does NaCl melt at a much higher temperature than glucose

A

Ionic bonds are harder to change the state of

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5
Q

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

A

Impurities lower the melting point and range of the compound

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6
Q

Melting point of biphenyl

A

69-70 C

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7
Q

Melting point of mandelic acid

A

120-121 C

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8
Q

Melting point of benzoic acid

A

122-123 C

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9
Q

Melting point of malic acid

A

131-132 C

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10
Q

Melting point of cinnamic acid and urea

A

132-133 C

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11
Q

Melting point of sebacic acid

A

133-135 C

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12
Q

Melting point of benzoin

A

135-136 C

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13
Q

Melting point of malic acid

A

137-139 C

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14
Q

Ethanol is a good solvent for …

A

Nonpolar compounds

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15
Q

Water is a good solvent because

A

It is polar and therefore dissolves polar substances well

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16
Q

How are benzoic crystals shaped?

A

Flat, white crystals

17
Q

Oiling out occurs when …

A

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

18
Q

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

A

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

19
Q

Why is it sometimes necessary to filter a hot solution?

A

This helps filter out any insoluble impurities.

20
Q

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

A

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

21
Q

Define boiling point

A

The temperature at which a liquid changes to a gas

22
Q

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

A

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

23
Q

Why is experimental boiling point lower than literature?

A

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

24
Q

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

A

Distillation rate

25
Q

Explain why during distillation the first few drops are cloudy

A

First drops wash water off the condenser and appear cloudy

26
Q

Charcoal is used to …

A

Remove color

27
Q

Which is more polar; benzoic acid or acetanilide?

A

Benzoic acid

28
Q

Because benzoic acid is more polar we have to use NaOH

A

Because it is a more polar solvent

29
Q

Benzoic acid is more acidic because

A

The pKa value is lower

30
Q

Why are drying agents used?

A

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

31
Q

Dilution equation

A

M1V1=M2V2

32
Q

Why do you not use excess drying reagent?

A

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

33
Q

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

A

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

34
Q

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

A

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

35
Q

Criteria for a good extraction solvent

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

Organic Chemistry Lab (5 decks)

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