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O Chem 2 > Lab Exam 1 > Flashcards

Lab Exam 1 Flashcards

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1
Q

Do impurities lower or raise the melting point of a solid?

A

Lowers melting point

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2
Q

What are the apparatus needed to test melt in point of a solid?

A

Solid organic compound, thin walled capillary tubes, paraffin oil, laboratory thermometer, heating medium/hot plate, magnetic stirrer, 500ml beaker, retort stand and rubber band

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3
Q

What is paraffin oil used for when investigating melting point?

A

Rub it on the bulb of the thermometer before being attached to capillary tube

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4
Q

What are the apparatus for preparing AND purifying ethyl acetate/ ethyl ethanoate?

A 
Chemicals: 
Acetic acid, 17.4M(glacial)
Ethanol
Concentrated sulfric acid(18M)
Equipment:
2 Erlenmyer flasks/conical flasks, 125mL
Boiling stones or glass beads 
Condenser
Distilling flask
Beaker 400mL for water bath
Bunsen burner, ring and wire gauze 
Measuring cylinder
Capillary dropper
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5
Q

Give the procedure for preparing ethyl acetate

A
  1. Place 10mL of ethanol, 12mL glacial acetic acid and 15 drops of concentrated sulfric acid and a boiling stone in an Erlenmeyer flask
  2. Clamp the condenser in a vertical position with the bottom inside the conical flask. This allows the condenser to act as a reflux condenser allowing mixture vapors to return to the mixture
  3. Slowly run cold water through the condenser, in the bottom and out of the top while heating the flask in a water bath
  4. Raise the temperature of the hot water until the mixture in the Erlenmeyer flask is gently boiling and continue for 15 mins
  5. Cool the mixture
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6
Q

What is the procedure for distillation of ethyl acetate?

A
  1. Pour the mixture of ethyl acetate(and boiling stone) into a distilling flask and connect the condenser to the side arm of the flask
  2. Insert thermometer
  3. Heat the bottom of the distilling flask in a hot water bath until no more distillate is coming over
  4. Record the temperature at which the distillation begins and the temperatures during and at the end of distillation
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7
Q

In preparation of ethyl acetate, why is the condenser clamped in a vertical position with the bottom inside the flask?

A

It acts as a reflux condenser , allowing vapors of the mixture to condense and return to the reaction vessel

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8
Q

What are precautions when investigating reactions between alcohols and phenols?

A
  1. Sodium dichromate is a toxic compound, so plastic gloves were used
  2. H2SO4 and HCl are very corrosive so there were
  3. Standard lab precautions used
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9
Q

What are precautions to be considered when finding the melting points of solids?

A
  1. Use dry and powdered sample for melting point determination
  2. Packing of the powder should be uniform without any big air gaps between the solid particles
  3. The capillary tube should be filled one fifth of its length
  4. Maintain uniform temperature of the liquid bath
  5. The rate of heating should be controlled and should be very slow near the melting point so that the melting point is recorded accurately
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10
Q

In testing the reactivity of alcohols and phenols, what is the method for esterification?

A

Add 1cm3 of glacial ethanoic acid, a few drops to concentrated sulfric acid to 2cm3 of the alcohol

Heat the mixture in a water bath

Pour the resulting mixture into water and note the smell

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11
Q

In testing reactivity of alcohols and phenols, write the method for oxidation

A

Add 2mL of 1% sodium dichromate and 5 drops of concentrated sulfric acid to each of the solutions and mix the contents thoroughly. Add 10 drops of each of the newly formed solutions to test tubes.

Cork all tubes and warm gently at 40-50 degrees Celsius in a water bath for 1 minute. Note any changes

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12
Q

Describe the triiodoform test

A

Add 5 drops of ethanol to 5 cm3 of iodine. Add NaOH until the iodine color has discharged and warm the mixture in a water bath for 2-3 minutes( temperature less than 60 degrees Celsius) cool the tube and note the crystals formed.

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13
Q

List three qualitative tests for alcohols

A

Jones oxidative test

Lucas test

Triiodoform test

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14
Q

Describe all possible results for the Lucas test

A

Primary alcohol- reacts slowly or not at all

Secondary alcohol- reacts in 1-5 minutes

Tertiary alcohol- reacts in less than a minute

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15
Q

What are the requirements for the iodoform test to be positive?

A

C attached to the -OH must also be bonded to a methyl group and hydrogen

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16
Q

What are the possible positive tests for the iodoform test?

A

Test positive for secondary alcohols and ethanol

17
Q

What are positive possibilities for Jone’s test?

A

Positive for primary and secondary alcohols

18
Q

What is the color change for jones oxidation?

A

From orange dichromate ion to greenish blue chromic ion if positive

19
Q

What shows a positive iodoform test?

A

Formation of a pale yellow precipitate of triiodomethane

20
Q

List 3 tests to differentiate between aldehydes and ketones

A
  1. Tollens test
  2. Jone’s oxidation
  3. Fehling’s/Benedict’s test
21
Q

What is the change that indicates a positive Fehling’s/Benedict’s test?

A

Change from blue solution(cupric oxide) to formation of a red precipitate( cuprous oxide)

22
Q

What is shows a positive test for Tollenks test?

A

Formation of a silver mirror

23
Q

What are the 12 laboratory rules?

A
  1. Lab coat must always be worn in the lab
  2. Shoes must have closed toes and heals
  3. Gloves should be worn during the lab exercises
  4. Don’t pipette solutions with mouth, eat, drink, smoke or apply cosmetics
  5. Never pour any chemical in the sink without authorization
  6. Never use flames with or near volatile solvents
  7. Never return reagents to stock bottles
  8. Never smell specimens or chemicals directly
  9. Use caution when using equipment for heating
  10. Always report any spillage or accident
  11. Wash hands thoroughly with soap and water
  12. Ask your instructors when in doubt
24
Q

In testing reactions of alcohols and phenols, what is the method for solubility?

A

Place 1mL of each alcohol and add an equal amount of water and dis litmus paper in the resulting solution

25
Q

In testing reactions of alcohols and phenols, what is the method of ignition?

A

Place 1 mL of each alcohol in a crucible and ignite

26
Q

How should the solubility of phenol be tested?

A

Take enough phenol to cover the bottom of the test tube and 2cm3 of water. Stopper the solution and shake to obtain an emulsion, remove the cork and place the test tube in a beaker of water and warm.

Put a thermometer in the solution to note when the emulsion clears. Test the solution in litmus paper and cool the solution

27
Q

Why was Iron 3 chloride used to be added to aqueous phenol? What color changes were there?

A

This is the ferric chloride test, used to distinguish phenols from alcohols. Solution went from white to purple

28
Q

Name 3 tests to identify phenol.

A

Ferric Chloride test

Bromine water test

Lieberman test

29
Q

Describe the Lieberman test

A

Phenol is mixed with solid sodium nitrate and concentrated sulfric acid and heated.

30
Q

What color is produced from a positive libermann test? What color does the solution turn upon the addition of water?

A

Solution has a green positive test

Solution turns red upon addition of water( due to forming indophenol)

31
Q

What color does indophenol become upon addition of excess caustic soda? Solution becomes blue, explain this

A

Solution becomes blue due to forming sodium salt of indophenol

32
Q

What shows a positive test for phenol in bromine-water?

A

White precipitate of 2,4,6-tribromophenol is formed

33
Q

Describe the bromine-water test

A

Red-bromine water is added to phenol

34
Q

Describe the ferric chloride test

A

Add one or two drops of ferric chloride solution to 3-4 drops of phenol

35
Q

Why does ferric chloride test produce a violet solution?

A

Purple solution due to differing hexaphenate formation

O Chem 2 (22 decks)

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