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Experiment : measuring reaction rates


To measure the effect of concentration on the rate of a reaction.


  • 300 cm 3 of sodium thiosulphate (Na 2 S 2 O 3 ) solution. Prepare a solution of sodium thiosulphate by adding 12 g of Na 2 S 2 O 3 to 300 cm 3 of water. This is solution 'A'.
  • 300 cm 3 of water
  • 100 cm 3 of 1:10 dilute hydrochloric acid. This is solution 'B'.
  • Six 100 cm 3 glass beakers
  • Measuring cylinders
  • Paper and marking pen
  • Stopwatch or timer


One way to measure the rate of this reaction is to place a piece of paper with a cross underneath the reaction beaker to see how quickly the cross is made invisible by the formation of the sulfur precipitate.

  1. Set up six beakers on a flat surface and mark them from 1 to 6. Under each beaker you will need to place a piece of paper with a large black cross.
  2. Pour 60 cm 3 solution A into the first beaker and add 20 cm 3 of water
  3. Use the measuring cylinder to measure 10 cm 3 HCl. Now add this HCl to the solution that is already in the first beaker (NB: Make sure that you always clean out the measuring cylinder you have used before using it for another chemical).
  4. Using a stopwatch with seconds, record the time it takes for the precipitate that forms to block out the cross.
  5. Now measure 50 cm 3 of solution A into the second beaker and add 30 cm 3 of water. To this second beaker, add 10 cm 3 HCl, time the reaction and record the results as you did before.
  6. Continue the experiment by diluting solution A as shown below.
Beaker Solution A (cm 3 ) Water (cm 3 ) Solution B (cm 3 ) Time (s)
1 60 20 10
2 50 30 10
3 40 40 10
4 30 50 10
5 20 60 10
6 10 70 10

The equation for the reaction between sodium thiosulphate and hydrochloric acid is:

N a 2 S 2 O 3 ( a q ) + 2 H C l ( a q ) 2 N a C l ( a q ) + S O 2 ( a q ) + H 2 O ( l ) + S ( s )


  • Calculate the reaction rate in each beaker. This can be done using the following equation:
    R a t e o f r e a c t i o n = 1 t i m e
  • Represent your results on a graph. Concentration will be on the x-axis and reaction rate on the y-axis. Note that the original volume of Na 2 S 2 O 3 can be used as a measure of concentration.
  • Why was it important to keep the volume of HCl constant?
  • Describe the relationship between concentration and reaction rate.


The rate of the reaction is fastest when the concentration of the reactants was the highest.

Mechanism of reaction and catalysis

Earlier it was mentioned that it is the collision of particles that causes reactions to occur and that only some of these collisions are 'successful'. This is because the reactant particles have a wide range of kinetic energy, and only a small fraction of the particles will have enough energy to actually break bonds so that a chemical reaction can take place. The minimum energy that is needed for a reaction to take place is called the activation energy . For more information on the energy of reactions, refer to Grade 11.

Activation energy

The energy that is needed to break the bonds in reactant molecules so that a chemical reaction can proceed.

Even at a fixed temperature, the energy of the particles varies, meaning that only some of them will have enough energy to be part of the chemical reaction, depending on the activation energy for that reaction. This is shown in [link] . Increasing the reaction temperature has the effect of increasing the number of particles with enough energy to take part in the reaction, and so the reaction rate increases.

Questions & Answers

what does organic mean
ntuthuko Reply
it means "from living thing"
What is a successful collision?
Refiloe Reply
It's a collision that results to a reaction
what is the factor and reaction rate of 20%HCL and 5%HCL
Kleng Reply
concentration and 0.05M/s
how you reaching with apartment depends on what each of you have
Edelita Reply
how with 4looseyellowprotons in your left hand stars are mostly hydrogen so this is your fuel you will also need one six so did die
besides the concentration what are the two conditions for the hydrogen half cell to function under standard conditions
Malwandla Reply
forces of non-concervative
Marlet Reply
What is the following process is likely to involve carbon burning?
Sofie Reply
Which Statement is part of the cell theory?
Hananiya Reply
What is the second formal statement in the cell theory
what is meant by ohmic
nthabiseng Reply
when someone is referred to as ohmic, it basically means that it obeys ohm's law
what is photosynthesis
Sihle Reply
is process whereby green plants to convert light energy into chemical energy.
what is an isomer?
Kiba Reply
organic compounds with the same molecular formula but different structural formula
how is frequency directly proportional to kinetic energy max. and what is the relationship between the wavelength and the energy of a photon. eg if a photon with a greater wavelength and a photon with less frequency. what would be the energies. as in which one would be greater and why
Pearl Reply
relationship wave depend n enrgy greadt reflect of energy n the form of tex shape
what is Cell capacity?
liphelo Reply
what are hydrocarbons
Nyiko Reply
compounds that are made up of hydrogen and carbon only
They are compounds that consist only with hydrogen &carbon elements.
how do i calculate the work done on an object by a frictional force
Emmelda Reply
@ Emmelda it's W = FxCos180 Where 180° is the angle between Frictional force and where the object is going, it's always 180° because it opposes the motion. Then F is the magnitude of the force and x is the displacement

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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