[PDF] [PDF] Core practical 4: Investigate the hydrolysis of halogenoalkanes

[PDF] Detailed Notes - Topic 33 Halogenoalkanes - AQA Chemistry A-level

Halogenoalkanes contain polar bondsas the halogens are more electronegative than carbon atoms This means electron density is drawn towards the halogen forming ∂+ and ∂- regions They must be shown with the lone electron pair and often a negative signindicating they are nucleophiles

[PDF] Core practical 4: Investigate the hydrolysis of halogenoalkanes

Part 1 1 Set up a water bath Fill the 250 ml beaker up to the three quarters mark with water, at around 50 °C 2 Fill three test tubes each with 5 cm3 of ethanol

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Core practical 4

Teacher sheet

Investigate the hydrolysis of halogenoalkanes

Practical activities have been safety checked but not trialled by CLEAPSS. Users may need to adapt the risk assessment information to

local circumstances. Core practical 4: Investigate the hydrolysis of halogenoalkanes

Objective

halo geno alkanes and of chloro -, bromo-, and iodoalkanes Safety Specification links

Obtain hot water from a kettle rather than using

Part 1

1. ௗ

to the three quarters mark with water, at

2. ௗ3

of ethanol.

Now add four drops of 1

-iodobutane to the first tube, four drops of 1 -bromobutane to the second tube and four drops of

1-chlorobutane to the third tube. Label the

tubes.

3. Loosely place a bung in each test tube and

place the test tubes in the water bath.

4. Pour 5ௗcm3

of silver nitrate solution into three clean test tubes.

Now place the test tubes in

the water bath.

5. When the halogenoalkane-ethanol solutions

have reached the temperature of the water bath , add the silver nitrate solution to one of the halogenoalkane -ethanol solutions and replace the bung. Start the stop clock as you do so.

6. Measure the time taken for the precipitate to

appear. As soon as the solution becomes cloudy stop the stop clock.

7. Repeat steps 5 and 6 for the other two

halogenoalkanes.

Part 2

8. Repeat Part 1 using 1-bromobutane, 2-

bromobutane and 2 -bromo-2-methylpropane be very slow. It is possible that a precipitate will not form in a reasonable time period. Instruct the students to stop timing after 10 minutes. silver nitrate solution should be kept in the water bath.

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Core practical 4

Teacher sheet

Investigate the hydrolysis of halogenoalkanes

Practical activities have been safety checked but not trialled by CLEAPSS. Users may need to adapt the risk assessment information to local circumstances.

Answers to questions

1. CH 3 CH 2 CH 2 CH 2

Br + H

2 O CH 3 CH 2 CH 2 CH 2

OH + H

+ Br

2. silver iodide

3. The halogenoalkanes are insoluble in water. Using ethanol ensures that the halogenoalkane

dissolve s so it can react with the water molecules.

4. Water has lone pair(s) of electrons on the oxygen atom.

5. If hydroxide ions were used, a precipitate of silver hydroxide would form instantly.

6. primary primary primary secondary tertiary

Sample data

Part 1

Halogenoalkane Time taken for a precipitate to form/s

1-iodobutane 52

1-bromobutane 87

1-chlorobutane 606

Part 2

Halogenoalkane Time taken for a precipitate to form/s

1-bromobutane 59

2-bromobutane 34

2-bromo-2-methylpropane 3

EDEXCEL Chemistry Teacher Resource Pack 1

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6 This document may have been altered from the original 1

Core practical 4

Student sheet

Investigate the hydrolysis of halogenoalkanes

Practical activities have been safety checked but not trialled by CLEAPSS. Users may need to adapt the risk assessment information to local circumstances. Core practical 4: Investigate the hydrolysis of halogenoalkanes

Objective

halo geno alkanes and of chloro -, bromo-, and iodoalkanes

Safety

All the maths you need

Equipment

3 beaker 3 ethanol 3 measuring cylinder

Procedure

Part 1

1. ௗ

2. ௗ

3 of ethanol. Now add four drops of 1-iodobutane to the first tube, four drops of 1 -bromobutane to the second tube and four drops of

1-chlorobutane to the third tube. Label the tubes.

3. Loosely place a bung in each test tube and place the test tubes in the water bath.

4. Pour 5ௗcm

3 of silver nitrate solution into three clean test tubes. Now place the test tubes in the water bath.

5. When the halogenoalkane-ethanol solutions have reached the temperature of the

water bath , add the silver nitrate solution to one of the halogenoalkane-ethanol solutions and replace the bung. Start the stop clock as you do so.

6. Measure the time taken for the precipitate to appear. As soon as the solution

becomes cloudy stop the stop clock.

7. Repeat steps 5 and 6 for the other two halogenoalkanes.

Part 2

8. Repeat Part 1 using 1-bromobutane, 2-bromobutane and 2-bromo-2-methylpropane

instead of the other halogenoalkanes.

Analysis

of results

1. Record your results for Part 1 and Part 2 in a suitable way.

2. What is the pattern shown in Part 1?

3. What is the pattern shown in Part 2?

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Core practical 4

Student sheet

Investigate the hydrolysis of halogenoalkanes

Practical activities have been safety checked but not trialled by CLEAPSS. Users may need to adapt the risk assessment information to local circumstances.

Learning tip

s neutralised by HNO 3 before adding AgNO 3

Questions

1. Write an equation for the reaction of 1-bromobutane with water.

2. In these reactions a precipitate forms. Identify the precipitate formed when the

halogenoalkane is 1 -iodobutane.

3. Explain why ethanol is used in these reactions.

4. Explain why water is able to act as a nucleophile.

5. Explain why water is used as the nucleophile rather than hydroxide ions?

6. Draw skeletal formulae for each of the halogenoalkanes used in this investigation

EDEXCEL Chemistry Teacher Resource Pack 1

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This document may have been altered from the original 1

Core practical 4 Technician sheet

Investigate the hydrolysis of halogenoalkanes

Practical activities have been safety checked but not trialled by CLEAPSS. Users may need to adapt the risk assessment information to local circumstances. Core practical 4: Investigate the hydrolysis of halogenoalkanes

Objective

halogenoalkanes and of chloro -, bromo-, and iodoalkanes

Safety

Equipment per student/group Notes on equipment

250
ௗcm 3 beaker

12 test tubes

1-chlorobutane

Students need access to the organic reagents

but need not have access to individual bottles.

1-bromobutane

1-iodobutane

2-bromobutane

2-bromo-2-methylpropane

silver nitrate solution Of same concentration as used for halide identification tests dropping pipettes 15 cm 3 ethanol two 10ௗcm 3 measuring cylinders stop clock labels for test tubes kettle Notesquotesdbs_dbs17.pdfusesText_23