CP5

Nucleophilic substitution

Because the carbon-halogen bond is polar due to a large difference in electronegativity

Water

Because there are 2 lone pairs of electrons on each oxygen atom

The halogen present (Cl, Br, I) and the type of halogenoalkane (primary, secondary, tertiary)

Wear eye protection; keep halogenoalkanes and ethanol away from flames; avoid skin contact with silver nitrate and hot water

To increase the temperature and speed up the reaction

Neutralise excess NaOH with HNO₃ before adding AgNO₃ to prevent brown AgOH precipitate

CH₃CH₂CH₂I + H₂O → CH₃CH₂CH₂OH + I⁻ + H⁺

AgCl – white, AgBr – cream, AgI – yellow

Halogenoalkanes are insoluble in water; ethanol dissolves them so they can react with water

Rate increases down group 7 because C–X bond strength decreases, so iodoalkanes hydrolyse fastest

Tertiary > secondary > primary (tertiary halogenoalkanes hydrolyse fastest)

1-Set up a water bath using a 250 cm³ beaker with water around 50°C

2-Take three test tubes and add 5 cm³ of ethanol to each one

3-Add four drops of 1-iodobutane to the first test tube, 1-bromobutane to the second test tube and 1-chlorobutane to the third test tube

4-Loosely place bungs in the test tubes and place them in a water bath

5-Take three clean test tubes and pour 5 cm³ of silver nitrate solution into each one and also place in the water bath

6-When the halogenoalkane-ethanol solutions have reached the temp of the water bath, add a silver nitrate to each test tube and measure the time taken for the precipitate to form
3 times.

7-Repeat step 6 using the primary, secondary and tertiary haloalkane

-Ensure that the water bath is at the correct
temperature to control the temperature of the
halogenoalkane.

-Use of lower temperatures to reduce the rates of reaction
as it makes the time difference between the
halogenoalkanes larger, giving a lower uncertainty.