RPA rate of hydrolysis of halogenoalkanes

Question 1

What is a hydrolysis reaction?

Answer 1

a type of reaction where water is used to break (hydrolyse) chemical bonds and split a reactant into two

Question 2

How do you test the rate of hydrolysis of different halogenoalkanes?

Answer 2

In 3 different test tubes add 4 drops of 1-chlorobutane, 1-bromobutane and 1-iodobutane
Add 5cm3 of ethanol to each test tube, and then place all test tubes in a 50C water bath
Pour about 5cm3 of silver nitrate into 3 test tubes, place the test tubes in the water bath
When all the solutions have reached 50C add the silver nitrate to the haloalkane- ethanol solutions
Start the stop clock, measure the time taken for each precipitate to appear

Question 3

What are the expected results of these reactions?

Answer 3

1-chlorobutane –> white precipitate slowly forms
1-bromobutane –> cream precipitate forms faster than that of 1-chlorobutane but slower than 1-iodobutane
1-iodobutane –> yellow precipitate forms very quickly

Question 4

How do you test the rate of hydrolysis of different haloalkanes?
primary, secondary, tertiary

Answer 4

3 different test tubes, add 4 drops of 1-bromobutane, 2-bromobutane and 2-bromo-2-methylpropane
add 5cm3 of ethanol, place the test tubes in a 50C water bath
Pour about 5cm3 of silver nitrate into 3 test tubes, place the test tubes in the water bath.
When all the solutions have reached 50C, add the silver nitrate solution to the haloalkane-ethanol solution
Start the stop clock, measure the time taken for each precipitate to appear

Question 5

what are the expected results of the reactions for testing the rate of hydrolysis of different haloalkanes- primary, secondary, tertiary

Answer 5

1-bromobutane -> slow formation of cream precipitate
2-bromobutane -> medium formation of cream precipitate
2-bromo-2-methylpropane –> fast formation of cream precipitate

Question 6

what kind of reaction is the hydrolysis of haloalkanes

Answer 6

nucleophilic substitution

Question 7

why are water baths used

Answer 7

to keep the temperature constant (as temperature is a control variable) so it doesn’t interfere with the rate of hydrolysis

Question 8

what is uncertainty

Answer 8

the uncertainty in a measurement is the interval within which the true value is expected to lie

Question 9

how do you calculate percentage uncertainty

Answer 9

100 x absolute uncertainty/ calculated value

Question 10

how can you decrease the uncertainty in time taken

Answer 10

use a lower temperature to reduce the rate of reaction

this will make the time taken longer and so the percentage uncertainty will be lower