1What is the name of the mechanism for the hydrolysis of halogenoalkanes?
Nucleophilic substitution
2Why can halogenoalkanes undergo nucleophilic substitution reactions?
Because the carbon-halogen bond is polar due to a large difference in electronegativity
3What is the nucleophile used in the hydrolysis of halogenoalkanes?
Water
4Why can water act as a nucleophile?
Because there are 2 lone pairs of electrons on each oxygen atom
5Name two variables that affect the rate of hydrolysis of halogenoalkanes
The halogen present (Cl, Br, I) and the type of halogenoalkane (primary, secondary, tertiary)
6What safety precautions must be taken when investigating the rate of hydrolysis of halogenoalkanes?
Wear eye protection; keep halogenoalkanes and ethanol away from flames; avoid skin contact with silver nitrate and hot water
7Why is a water bath used when investigating hydrolysis of haloalkanes?
To increase the temperature and speed up the reaction
8What must be done if NaOH is used to hydrolyse halogenoalkanes? Why?
Neutralise excess NaOH with HNO₃ before adding AgNO₃ to prevent brown AgOH precipitate
9Write an equation for the reaction between 1-iodopropane and water
CH₃CH₂CH₂I + H₂O → CH₃CH₂CH₂OH + I⁻ + H⁺
10What colours are the precipitates when halide ions react with AgNO₃?
AgCl – white, AgBr – cream, AgI – yellow
11Why is ethanol used when halogenoalkanes are hydrolysed?
Halogenoalkanes are insoluble in water; ethanol dissolves them so they can react with water
12How does the halogen affect the rate of hydrolysis?
Rate increases down group 7 because C–X bond strength decreases, so iodoalkanes hydrolyse fastest
13How does the type of halogenoalkane affect rate of hydrolysis?
Tertiary > secondary > primary (tertiary halogenoalkanes hydrolyse fastest)
14what is the method to find the rates of hydrolysis of halogenoalkanes (include steps)
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
15what are the possible sources of error for the hydrolysis reaction
-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.