ADVANCED LEVEL CHEMISTRY PRACTICAL
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Candidate Number |
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Centre Number |
71637 |
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Name |
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Date |
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PREPARATION OF BROMOETHANE |
INTRODUCTION
Bromoethane is an alkyl
halide and can be prepared from the corresponding alcohol by reaction with
hydrogen bromide. This is usually prepared 'in situ' by the reaction of
concentrated sulphuric acid and sodium or potassium bromide. Bromoethane is a liquid with a boiling point
of 39oC and a density of about 1.5 g
cm-3. It is immiscible with water. The reaction takes place in 2 stages:
the alcohol is protonated by the sulphuric acid and then a water molecule is
displaced by a bromide ion.
C2H5OH + H+ C2H5OH2+
C2H5OH2+ + Br- C2H5Br + H2O
PROCEDURE
1. Pour 16 cm3 of ethanol into a
100cm3 distilling or pear shaped flask. Put 3 or 4 anti-bumping
granules in the flask.
2. Add, in about 5 portions, 10cm3
of concentrated sulphuric acid swirling the flask between each addition and
cooling under the tap.
3. When the mixture is at about room
temperature quickly add 10g of potassium bromide and at once set up for
distillation. The adapter should be dipping under cold water in the receiver (a
small flask).
4. Warm so that the contents just boil gently and continue distilling until no
more oily droplets of bromoethane are passing into the receiver.
5. Stop heating and disconnect the adapter.
6. Decant off as much as possible of the
water from the receiver.
7. Transfer the remainder of the receiver
mixture into a separating funnel. Add about 10cm3 of sodium
carbonate solution to the funnel and shake, releasing the gas from time to
time.
8. Run off the lower organic layer, retain
it, and discard the aqueous layer.
9. Return the bromoethane layer to the
funnel, add a little water and shake as before.
10. Run the lower layer into a small flask
containing some anhydrous calcium chloride, cork and allow to dry.
11. Decant the liquid into a distilling flask,
add anti-bumping granules and distil using a water bath. Collect the fraction
boiling between 35oC and 43oC in a weighed conical flask and determine
the yield.
Yield
of bromoethane = g
QUESTIONS
1. What is the role of the anti-bumping
granules?
2. Why is the acid added in portions and with
cooling?
3. Why is the potassium bromide added all at
once and then the distillation apparatus set up quickly?
4. What is the product between the acid and
the potassium bromide?
5. Why does the adapter have to dip into the
water?
6. What might happen if the heating was too
strong?
7. Why is the adapter disconnected after the
heating is stopped?
8. Why is the sodium carbonate added?
9. How is a separating funnel used safely?
10. What is the function of the anhydrous
calcium chloride?
11. If the density of ethanol is 0.79 g cm-3
calculate the number of moles of it used.
12. Calculate the maximum mass of bromoethane
that could be formed. This is usually referred to as the theoretical yield.
ADVANCED LEVEL CHEMISTRY PRACTICAL
ASSESSMENT CHECKLIST
|
Candidate
Number |
|
Centre
Number |
71637 |
|
Name |
|
Date |
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PREPARATION OF BROMOETHANE
SKILL 2 manipulation Student Mark
Goggles
(1)
Use of graduated cylinder (2)
Addition of sulphuric acid (2)
Distillation (3)
Separating funnel (3)
Drying (1)
Fractional distillation ( 3)
TOTAL 15 marks
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TOTAL |
0 |
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SCALED MARK |
0 |
1 |
2 |
3 |
4 |
5 |
SKILL 3 MEASURING & RECORDING Student
Mark
Volume of ethanol 1
Volume of sulphuric acid 1
Mass of potassium bromide
1
Fraction between 35oC-43oC 2
[5]
TOTAL marks
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TOTAL |
0 |
|
|
|
|
|
|
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
Question 1 1
Question 2 1
Question 3 2
Question 4 1
Question 5 1
Question 6 1
Question 7 1
Question 8 1
Question 9 2
Question 10 1
Question 11 1
Question 12 2
TOTAL
15 marks
|
TOTAL |
0 |
1-2 |
3-4 |
5-6 |
7-8 |
9-10 |
|
SCALED MARK |
0 |
1 |
2 |
3 |
4 |
5 |