Rate of Reaction Experiment - Sodium Thiosulphate and Hydrochloric Acid
To investigate the effect, of changing the concentration of a
reactant, in a chemical reaction on it rate.
The equation used for the experiment was:
Sodium + Hydrochloric Sulphur + Sulphur + Sodium + water
Thiosulphate acid dioxide chloride
Na2S2O3 + 2HCl(aq) S(s) + SO(g) + NaCL(aq) + H2O
The Collision Theory can explain reaction rates perfectly. A chemical
reaction can only occur between particle when they hit or collide at a
minimal amount of energy need for them to react this is called the
The rates of a reaction depends on how hard and often the reacting
Basically, particles have to collide in order to react
1) They must also collide hard enough to give a reaction.
2) Pressure can also affect reaction rates between gases, an increase
in pressure pushes the molecules closer together making them collide
more often, which in turn increases the reaction rate.
3) A presence of a Catalyst could affect the result, as it is a
substance that alters the rate of the reaction. without itself
appearing in the final result.
When a solution becomes more concentrated it means there are more
particles of reactant knocking between the water molecules, this means
collisions between important particles more likely.
In a gas, increasing the pressure means the molecules are more
squashed together, there will then be lots more collisions.
Higher temperature also increases the energy of the collisions, it
makes particles move faster. Faster collisions can only b caused by
increasing the temperature. enzymeThis is shown in the diagram
The Maxwell-Boltzmann Distribution and activation energy
For a reaction to take place particles have got to collide with
energies greater than or equal to the activation energy for the
reaction, this can be marked on Maxwell-Boltzmann Distribution.
I have chosen to investigate the effect concentration has on a
reaction. I chose this because it is the easier to prepare and will
provide the most accurate set of results.
Paper with black cross on
To provide fair accurate results it is important to ensure that the
same printed cross is used for each experiment. In this the experiment
the amount of Sodium Thiosulphate is varied each time in comparison to
the amount of water used, the solution will always add up to 45cm3.
There will always be 5cm3 of hydrochloric acid used. The experiment
was performed at room temperature as this made the experiment easy to
perform, as no heating or cooling devises were necessary. By taking
these precautions it will keep the experiment accurate and keep
anomalies to a minimum.
Safety goggles were put on and all equipment was set up ensuring the
experiment was performed with maximum efficiency
A conical flask was placed over the X marked on the piece of paper.
The required amounts of Sodium thiosulphate and water were measured
out and mixed.
The mixture of sodium thiosulphate and water was mixed in a conical
flask already containing the Hydrochloric acid, the stopwatch began
timing as soon as both the reactants were in.
The stopwatch was stopped when the X marked on the piece of paper was
no longer visible through the mixture.
The results were recorded in a table and the equipment was cleaned
thoroughly ready for the next experiment.
To ensure the reliability of my result, the experiment was performed
twice, if I had been allocated more time I would have preformed the
experiment a 3rd time to make my results even more reliable.
I predicted that the reaction rate would be quicker the more Sodium
Thiosulphate present. I also think that the increase in time taken
will also be a gradual one.
There were no anomalous results during the experiment and so all
results were used to find the mean time, this gave more reliable
results. The graph clearly shows that the lower the volume of Sodium
Thiosulphate the longer it takes for the cross not to be visible, this
is as I predicted. The average time taken for the cross to disappear
shows a gradual rise up until between 5cm3 and 2.5 cm3, where it
slopes dramatically showing the effect the lack of Sodium Thiosulphate
has on the reaction time.
The results I have produced are not entirely accurate as most of the
measurements have been left up to human judgement. For example judging
whether the cross has become invisible could vary each time and would
be more accurate if a machine had been used to taker the measurement.
Also using a stopwatch instead of a wristwatch would also make the
results more reliable. Despite this I still think the results produced
were of an adequate level of accuracy need for this experiment.
If I had the opportunity to do this experiment again I would use a
more accurate way of measuring whether the reaction had reached a
certain stage and would also use a much more accurate meter to measure
the time taken. I would also repeat the experiment a few more times to
again increase its accuracy.