ADVANCED
LEVEL CHEMISTRY PRACTICAL ASSESSMENT
|
Candidate Number |
|
Centre Number |
71637 |
|
Name |
|
Date |
|
PREPARING
AN ESTER
SKILL AREAS ASSESSED : 1
Planning
2 Manipulation
3 Measuring & Recording
4 Observing & Recording
5 Concluding & Communicating
AIM
The
purpose of this experiment is to prepare a sample of phenyl benzoate, purify it
by recrystallisation ,and measure its melting point.
INTRODUCTION
You prepare phenyl
benzoate by shaking phenol with benzoyl chloride in alkalione solution.
C6H5COCl + C6H5OH C6H5CO2C6H5
+ HCl
APPARATUS CHEMICALS
A
safety spectacles phenol,
C6H50H
protective gloves 2
M sodium hydroxide solution
weighing bottle 10 cm3 benzoyl chloride
spatula
access to balance,
sensitivity 0.01 g
conical flask, 250 cm3, with tight-fitting rubber bung
measuring cylinder, 100
cm3
measuring cylinder, 10
cm3
B
water-bath or 250 cm3 beaker ethanol,
C2H50H
thermometer, 0-100 ¡C
ice
specimen bottle
access to balance,
sensitivity ± 0.1 g
C
thermometer. 0-100 ¡C
watch glass
***HAZARD WARNING***
Benzoyl chloride is
lachrymatory (produces tears), is irritating to the skin and can cause burns.
Phenol vapour is harmful
to the eyes, lungs, and skin. Solid and solution are corrosive and poisonous by
skin absorption.
Therefore you MUST:
WORK AT A FUME CUPB0ARD
WEAR
SAFETY GLASSES AND PROTECTIVE GLOVES
PROCEDURE
A. Preparation of phenyl
benzoate
1. Transfer about 5.0 g of phenol into a
weighing bottle and weigh it to the nearest 0.01 g.
2. Into a conical flask pour 90 cm3 of 2 M sodium hydroxide and the bulk of
the phenol from the weighing bottle.
3. Reweigh the weighing bottle, with any
remaining phenol, to the nearest 0.01 g.
4. In a fume cupboard pour 9 cm3 of benzoyl chloride into the conical
flask.
5. Insert the bung securely and shake the
bottle for15 minutes,
carefully releasing the
pressure every few minutes as the flask
gets
warm.
6. Cool the flask under cold, running
tap-water.
7. Filter the crude product using a suction
filtration apparatus. Use a spatula to break up the lumps of ester on the
filter paper, being careful not to puncture the filter paper.
8. Pour more water over the crude
ester to destroy any remaining benzoyl chloride.
B Recrystallization
1. Transfer the crystals to a boliing tube
and just cover them with ethanol
2. Place the boiling tube in a water-bath or
beaker of hot water, kept at about 60oC
and stir with the glass rod.
3. If some solid ester is still visible, add just
enough ethanol to dissolve it completely after stirring.
4. In order to allow the separation of the
ester as a solid rather than an oily liquid (phenyl benzoate has a low melting
point) add more ethanol to double the volume of solution.
5. Cool the solution in an ice-water mixture
until the crystals appear.
6. Filter the crystals using a BŸchner
suction apparatus, using a clean BŸchner funnel and filter paper. To avoid losing any solid break the vacuum
and use the filtrate to rinse the boiling tube into the funnel.
7. Using suction again, rinse the crystals
with about 1 cm3 of cold
ethanol and drain thoroughly.
8. Press the crystals
between two wads of filter paper to remove excess solvent. Then put the
crystals on another dry piece of filter paper placed alongside a Bunsen burner
and gauze, turning the crystals over occasionally until they appear dry. Don't
let them get too hot or they will melt!
9. Weigh the dry
crystals in a pre-weighed specimen bottle and record the mass of your sample of phenyl benzoate.
C. Determination of melting-point
Determine
and record the melting point of your sample of phenyl benzoate.
CONCLUDING & COMMUNICATING
QUESTIONS
1. Calculate
the maximum mass of phenyl benzoate that could be formed from the mass of
phenol you used, assuming complete conversion according to the equation.
2. Calculate
the percentage yield of phenyl benzoate
3.
The melting-point of pure phenyl
benzoate is 69 ¡C. What can you say about the purity of your sample?
ADVANCED
LEVEL CHEMISTRY PRACTICAL ASSESSMENT CHECKLIST
|
Candidate Number |
|
Centre Number |
71637 |
|
Name |
|
Date |
|
PREPARING
AN ESTER
SKILL
2 manipulation Student Mark
Safety
glasses and gloves worn throughout (2)
Correct
use of balance (2)
Safe
transfer of liquids (2)
Use
of fume cupboard for benzoyl chloride (2)
Shakes
flask for required time (1)
Releases pressure at intervals (1)
Büchner
filtration (2)
Control
of water bath temperature for ethanol (2)
Recrystallisation
(3)
Melting
point determination (3)
TOTAL 20 marks
|
TOTAL |
0-1 |
2-5 |
6-9 |
10-13 |
14-17 |
18-20 |
|
SCALED
MARK |
0 |
1 |
2 |
3 |
4 |
5 |
SKILL
3 MEASURING & RECORDING Student Mark
Mass
measured to required accuracy 2
Volume
of sodium hydroxide 2
Volume
of phenol 2
Records
mass of phenol used 2
Measures
temperature of water bath 1
Records
mass of dry crystals 2
Melting
point of crystals (70-71oC) 1
(69-70oC) 3
(68-69oC) 2
TOTAL
14 marks
|
TOTAL |
0-1 |
2-4 |
5-6 |
7-9 |
10-12 |
13-14 |
|
SCALED
MARK |
0 |
1 |
2 |
3 |
4 |
5 |
SKILL
4 OBSERVATION
& RECORDING Student
Mark
TOTAL marks
|
TOTAL |
0 |
|
|
|
|
|
|
SCALED
MARK |
0 |
1 |
2 |
3 |
4 |
5 |
SKILL
5 CONCLUDING & COMMUNICATING Student Mark
Calculation
of maximum mass of ester (2)
Calculation
of percentage yield of ester (2)
Percentage
yield (90-99%) (1)
(80-89%)
(2)
(70-79%)
(3)
(55-69%)
(4)
(50-54%)
(3)
(40-49%)
(2)
(30-39%)
(1)
Comment
on percentage yield (1)
Relates
melting point to purity of crystals (2)
Appropriate
comment on melting point (2)
TOTAL 13 marks
|
TOTAL |
0-1 |
2-3 |
4-6 |
7-9 |
10-11 |
12-13 |
|
SCALED
MARK |
0 |
1 |
2 |
3 |
4 |
5 |