Rates- experimental methods

HideShow resource information
  • Created by: Jessica
  • Created on: 22-04-13 13:57

experimental methods

the rate o reaction cannot be measured directly but can only be determined from concentration time data

1 of 10


1. measure out samples of the reactants with known concntrations

2. mix and start the clock

3. at regular intervals withdraw samples using a pippette ad quench- to stop the reactions from occuring in the sample that has been removed

this could be through adding ice to the pippetted sample- this slows down the rate of the reaction. addig a solution that reacts with one of the reactants also stops the reaction. 

4. the time at which haft of the contents of the pipette have been added to the queching solution should be notes

5. the quenching solution is then titrated against a standard solution

this will give the results for the concentration of the product produced as the reaction continues 

this method can be used for when an acid, alkali or iodine is a reactant or product

2 of 10


if a reactant or product is colouted the conctration of the coloured species can be measured using a spectrophotometer.

the amount of light of a particular frequncy that is absorbed depnds on the conctration fo the coloured substance

1. reactants are mixed and the clock starts

2. the light absorbed is measured at set time intervals

3 of 10

infrared spectroscopy

the amount of IR radiation absorbed at a particular frequency is measured at regular time intervals

4 of 10


can be used if a reactant/product  is optically active- and its optical activity is different from the product/ reactant 

the reaction is followed by measuring the extent to which the plane of plane polarised light is rotated

5 of 10

volume of gas evolved

if the reaction produces a gas the volume of gas produced ca be measured at regular time intervals

volume of gas is proportional to the moles of gas- concntration can be calculated

a gas syringe can be used to measure the volume of gas produced

6 of 10

time for the reaction to finish

add two reactants and time how long it takes for the reaction to stop 

the experiment can then be reapeated at different concntrations/ different temperatures 

7 of 10

iodine clock reaction

in clock reactions the reactants are mixed and the time taken to produce a fixed amount of product is measured. the experiment is repeated several times using different starting concntrations

1. hydrogen peroxide, water and starch are mixed in a beaker

2. potassium iodide and thiosulfate are moxed in another beaker

3. the contents of the two beakers are moxed and the time taken for the solution to go blue is measured

4. the experiment is repeated with different concentrations of the solutions 

8 of 10

sulfur clock reaction

1. X is drawn on a white tile

2. sodium thiosulfate solution is mixed with water

3. dilute nitric acid is placed in a second beaker

4. contents are mixed

5. the time taken for sulphur to be produced- so the X can no longer be see is measured

6. the experiment is repeated at different cocntrations 

9 of 10


change in pH over time can be measured 

10 of 10


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Rates resources »