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Experiment : measuring reaction rates

Aim:

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

Apparatus:

  • 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

Method:

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 )

Results:

  • 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.

Conclusions:

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

Is the normal force always 0
Mpilo Reply
no. newtons 3rd law states that if something exerts a force into something else it will experience that same magnitude of force but in the opposite direction. so the net force is equal to the force the object applies to the surface but in the opposite direction
Courtney
define the term rate of reaction in word
David Reply
I think it a chemical process in which substance act mutually on each other.
Sphesihle
how many bones are in the human body?
Asali
it's the rate at which the reactants are able to change to products
Courtney
what is wave lengh
mama Reply
is the de broglie wavelength of the particle
Hope
calcium and magnesium, which one can displace aluminum from its compound?
Markia Reply
how is aluminum ion formed?
Dickens
a substance that has the lower electronegativity which will be in this case the Ca -1.0 this is because the Ca would have a lower ionization energy -needs less energy to fill its outer most shell and therefore will cause a displacement of the Al
Courtney
an Al ion would form when it has lost electrons and will normally be a cation -positively charged (3+)
Courtney
molecules with the same molecular formula but different chain
Malaza Reply
what will be the answer
.angel
chain isomer
Anele
what does the newton's law says?
there are 3 newtons laws which are newton's law of universal gravitation, law of cooling, law of motion
Imagine
Did the feather or leaf hit the ground first?
Shaloom Reply
leaf
Pradip
both at the same time. air friction ignored
Courtney
2 to 30 minut long distance race 20 km what's the avarage speed for the race
Jamilla Reply
what is meaning of covalent bonds
Lungani Reply
bonds that exists between non metal atoms. each atom contribute electron(s) which will form a bond joining the two atoms. electrons in the bond now belongs to both atoms
Matome
how do we name haloalkanes
Thobeka Reply
how do we name haloalkanes
lesedi
what are examples of haloalkanes
Mpho
haloalkanes are compounds that consist of the halogen group chlorine bromine flourine and so on like 2-bromobutan
Samkele
give an example of calculating work
Nwabisa Reply
what is chain Isomer?
Christian Reply
chain isomer ar compounds with the same molecular formular but different chain length
Samkele
Where does the functional group of ketone in carbons belong
Keletso Reply
alkane
Isamkele
how can I find the structural formulae and IUPAC names of hexane?
Matshidiso Reply
@Matshidiso identify your compound which is an alkane..the general formula for alkane is CnH2n+2... hex-6 substitute n with 6 implying that you'll have 6 carbons and 14 Hydrogens then you can draw your structural formula *NB* every carbon has to have 4 bonds
Kgabo
what are disadvantages of primary cells and advantage of secondary cells?
Thabang Reply

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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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