ADVANCED LEVEL CHEMISTRY PRACTICAL ASSESSMENT
Candidate Number: Centre
Number:71637
Name:______________________
Date:____________
PREPARING AN ESTER
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 ĄC
ice
specimen bottle
access to balance,
sensitivity ± 0.1 g
C
thermometer. 0-100 ĄC
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 Bchner suction apparatus,
using a clean Bchner 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.
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 cf phenyl benzoate
3. The melting-point of pure phenyl benzoate is 69 ĄC. 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 AREA 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
Bchner
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 AREA 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 AREA 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 |