Investigating the rates of reaction of Sodium thiosulphate and hydrochloric acid
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Investigating the rates of reaction of Sodium thiosulphate and hydrochloric acid
Using my preliminary experiments I decided on using the following
- A conical Flask
- A piece of White Paper marked with a black cross
- Dilute hydrochloric acid
- Sodium thiosulphate
- Measuring cylinder
We must produce a piece of coursework investigating the rates of
reaction, and the effect different changes have on them. The rate of
reaction is the rate of loss of a reactant or the rate of formation of
a product during a chemical reaction. It is measured by dividing 1 by
the time taken for the reaction to take place. There are four factors
which affect the rate of a reaction, according to the collision theory
of reacting particles: temperature, concentration (of solution),
surface are (of solid reactants), and catalysts. I have chosen to
investigate the effect concentration has on a reaction.
This is because concentration is the most practical to investigate as
it would take longer to prepare a solid in powdered and unpowdered
form, and it is difficult to get accurate readings due to the
inevitabilities of human errors, and as gas is mostly colourless it is
difficult to gauge a reaction changing the pressure, and if a
substance is added to give the gas colour, it may influence the
outcome of the experiment.
Also temperature is difficult to sustain and be made exact for all the
Similarly the use of a catalyst complicates things, and if used
incorrectly could alter the outcome of the experiment.
All other factors however must be kept constant while we are varying
Both the sodium thiosulphate and the Hydrochloric acid are soluble in
water, so the concentration of either can be changed. However I have
chosen to vary the sodium thiosulphate as it is available in larger
amounts, and various concentrations are prepared.
I will time how long it will take varying concentrations of Sodium
Thiosulphate to react with the Hydrochloric acid so that the solution
when placed above the white paper with the black cross is so reacted
that one cannot see the cross through the opaque liquid.
In order for my findings to be valid the experiment must be a fair
one. I will use the same standard each time for judging when the X has
disappeared. I will make sure that the measuring cylinders for the HCl
and thiosulphate will not be mixed up. The amount of HCl will be 5 cm3
each time, and the amount of thiosulphate will be fixed at 20 cm3.
Also room temperature will be used as the temperature as it is
practical and will not need to be monitored.
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Rates Of Reaction Sodium Thiosulphate Hydrochloric Acid Various Concentrations Varying Concentrations Alter
We shall repeat this
process three times in order to get the most accurate average of
results possible. . All of these precautions will make my final
results more reliable and keep anomalies at a minimum so thus making
the entire investigation more successful.
The chemical equation for my experiment is:-
Na S O (aq)+ HCl(l) ( 2 Na Cl (aq) + H SO(aq) + S(s)
The sulphur (s) is the precipitate this is the component that causes
the solution to turn cloudy white when the reaction takes place. This
is the visual aid that tells how fast the reaction is taking place.
The speed of the reaction is what we are looking at as we can find out
the rate of a reaction by dividing 1 by the time taken for the
reaction to take place, the factors that cause the change in speed.
Some of these factors are :-
Reactions speed up when the temperature is increased,
Reactions speed up when the concentration is increased,
Reactions speed up when the surface area of the reactants increase.
In some cases reactions can speed up when the pressure around the
reaction is increased.
Reactions speed up when a catalyst is introduced.
We are only interested in the fact that reactions speed up when the
concentration is increased.
5 cm3 of HCl (at concentration 1 mol./dm3) and 20 cm3 of sodium
thiosulphate (at varying concentrations of 10 to 50 g/dm3) are poured
out into two measuring cylinders and then poured into a conical flask,
which is placed on top of a piece of paper marked with letter X. The
stopwatch will now be started. When the mixture has turned
sufficiently cloudy so that the letter X can no longer be seen the
stopwatch will be stopped and the time will be recorded. The
experiment is repeated with all the concentrations. The whole
procedure is then repeated twice in order to obtain the most accurate
I predict that as the concentration of the sodium thiosulphate
increases the rate of reaction will increase. This means that graphs
drawn up in my analysis will have positive correlation, and will
probably be curved as the increase in rate of reaction will not be
exactly the same as the concentration is increased. This can be
justified by relating to the collision theory.
If solutions of reacting particles are made more concentrated there
are more particles per unit volume. Collisions between reacting
particles are therefore more likely to occur. All this can be
understood better with full understanding of the collision theory
For a reaction to occur particles have to collide with each other.
Only a small percent result in a reaction. This is due to the energy
barrier to overcome. Only particles with enough energy to overcome the
barrier will react after colliding. The minimum energy that a particle
must have to overcome the barrier is called the activation energy, or
Ea. The size of this activation energy is different for different
reactions. If the frequency of collisions is increased the rate of
reaction will increase. However the percent of successful collisions
remains the same. An increase in the frequency of collisions can be
achieved by increasing the concentration, pressure, or surface area.
Concentration - If the concentration of a solution is increased there
are more reactant particles per unit volume. This increases the
probability of reactant particles colliding with each other.
Pressure - If the pressure is increased the particles in the gas are
pushed closer. This increases the concentration and thus the rate of
Surface Area - If a solid is powdered then there is a greater surface
area available for a reaction, compared to the same mass of unpowdered
solid. Only particles on the surface of the solid will be able to
undergo collisions with the particles in a solution or gas.
The particles in a gas undergo random collisions in which energy is
transferred between the colliding particles. As a result there will be
particles with differing energies. Maxwell-Boltzmann energy
distribution curves show the distribution of the energies of the
particles in a gas.
The main points to note about the curves are:
There are no particles with zero energy.
The curve does not touch the x-axis at the higher end, because there
will always be some particles with very high energies.
The area under the curve is equal to the total number of particles in
The peak of the curve indicates the most probable energy.
The activation energy for a given reaction can be marked on the
distribution curve. Only particles with energy equal or greater than
the activation energy can react when a collision occurs. Although
Maxwell-Boltzmann distribution curves are for the particles in a gas,
the same distributions can be used for the particles in a liquid or
I shall now put this information into graphs in order to see my
results more clearly and identify any trends or patterns. I shall show
these with rates of reaction but first I shall have to find these
rates of reaction:-
I have found out that the higher the concentration of the sodium
thiosulphate the quicker the reaction takes place i.e the rate of the
reaction increases with the concentration.
As we can see in my graph 1 there is a trend the graph shows a
negative correlation. The lower the concentration the longer the
reaction takes to take place. It is clear that looking at my results
that the higher the concentrations the closer the times of the
reactions are. In turn as the concentration of the sodium thiosulphate
decreases the times that we have seen are much further apart. I think
this will carry on until there are no longer enough sodium
thiosulphate particles for the activation energy barrier to be passed.
Graph 2 which plots the rate of reaction against the concentration of
the sodium thiosulphate, shows a positive correlation. Showing the
higher the concentration the higher the rate of reaction and the lower
the concentration the lower the rate of reaction
This is because when the concentration is increased the particles will
have more energy and thus move faster. Therefore they will collide
more often and with more energy. Particles with more energy are more
likely to overcome the activation energy barrier to reaction and thus
react successfully, and when solutions of reacting particles are made
more concentrated there are more particles per unit volume. Collisions
between reacting particles are therefore more likely to occur.
Therefore I can conclude that if the frequency of collisions is
increased the rate of reaction will increase. However the percent of
successful collisions remains the same. An increase in the frequency
of collisions can be achieved by increasing the concentration,
pressure, temperature, surface area or by experimenting with
In conclusion, I think that the effect of the concentration of the
sodium thiosulphate on the rate of reaction is this, that due to the
increase in concentration there are many more successful collisions
per second within the solution. This is why the higher the
concentration is the quicker the reactions are taking place resulting
in the rate of reaction increasing. It is also why the lower the
concentration the less successful collisions are happening per second
this is resulting in the rate of reaction decreasing.
My conclusion completely supports my prediction I predicted that the
higher the concentration the higher the rate of reaction and the lower
the concentration the lower the rate of reaction. I also predicted
that it would take much more time as the concentration of the sodium
thiosulphate decreased. All of the things that I predicted would
happen happened so my prediction was fairly accurate.
I think that considering the equipment available to me, and the time
scale that we had, it was a very good and fair procedure. I think this
shows in my results. I think that there were certain places in my
procedure that were left open for human error, e.g. Measuring the
correct volumes of the solutions, judging when the cross had
disappeared, starting and stopping the stop watch at the beginning and
Even though there were some areas that were not perfectly accurate we
got results that supported the facts. We were also able to carry out
the experiment in a short space of time with limited equipment, so I
think that it was a very successful experiment, which gave very
interesting and informative results. However, if I were to repeat the
experiment there would be a few things that I would change. I would
use machines to measure out the volumes of the liquids e.g. the
burette would be attached to a timer that opened and closed the tap
when the correct volume had been used. I would also use light
sensitive machines to judge when the cross was no longer visible, I
would also use light sensors to start and stop the stopwatch. They
could be fitted to the conical flask and could tell when the desired
volume had been acquired. I would hope that by taking all these
precautions I could eliminate the possibility of human error.
I think that the general quality of my results was good; they all
corresponded with the predictions that I made at the beginning of the
experiment. They all fitted in with the pattern that the higher the
concentration of the solution the higher the rate of reaction and the
lower the concentration the lower the rate of reaction.
I think that given the equipment I had my procedure was suitable,
however if I could have any budget and any amount of time I would, as
I have said before use light sensitive machines to do almost
everything in the hope that this would give me better results. There
was one result that was not really an anomaly as it still followed the
pattern but was slightly different to the other result of the other
test. When the amount of Sodium Thiosulphate was 10 cmÂ³, the time of
the second test was 180 secs compared to 136 in the first test and 140
in the third test.
In general I was very pleased with all of my results and I think that
they were reliable. There were some results that were not as close to
the others as I had hoped but I think this was mainly because of human
errors. e.g. when the person was judging when to stop the burette or
when the cross was no longer visible there was not enough care taken
by the person to get the measurements exactly right. It is however
also possible that it was not to do with the care taken just the
eyesight of the person doing the measuring/judging. However, these
results are sufficient for me to form a conclusion as I did not expect
exact results. I had an idea of what I expected and that idea was
realised so I knew my results were at least reliable in the way that
they followed the expected pattern.
If I had more time there would be a few things that I would like to do
to extend my investigation a little further. For example I would also
like to experiment with other variables such as pressure, temperature,
surface area or catalysts. I would like have varied the concentration
more and to a more accurate degree and to vary the volumes of the
solutions and have a larger range of concentrations in order to
understand reaction rates better.
I think that the evidence, which I have received, is enough to reach a
suitable conclusion, considering our time, equipment and knowledge
Investigating Reaction Rates Of Sodium Thiosulphate And Hydrochloric Acid
Investigating Reaction Rates of Sodium Thiosulphate and Hydrochloric
To investigate the rate of reaction of Sodium Thiosulphate and
Hydrochloric acid. In this investigation I will be varying the
concentration of Sodium Thiosulphate only and not the Hydrochloric
In this investigation I will use the following word equation:
Sodium Thiosulphate + Hydrochloric acid
In this investigation I will use the following symbol equation:
Na2S2O3 + Hcl
I predict that as the Sodium Thiosulphate concentration increases the
rate of reaction will also increase.
The reason I predict this is because there will be a higher
concentration of particles and so a faster reaction would be able to
occur- so the reaction rate would increase. There will be more
particles of Sodium Thiosulphate and Hydrochloric acid in a small
volume and so more collisions are likely to occur which in turn cause
a quicker rate of reaction.
In this investigation I used 25cm cubed of Sodium Thiosulphate and 5cm
cubed of Hydrochloric acid.
Health and Safety:
In order to make this investigation as safe as possible for myself I
took a number of precautions.
The first precaution that I took was to wear a lab coat and goggles.
The lab coat would protect my clothes from any acid spills or splashes
that may occur and the goggles would protect my eyes from being
affected by any acid spills or splashes.
My prediction has been based on my scientific theory. In the
investigation I carried out a chemical reaction occurred.
A chemical reaction is when two substances collide with each other and
form new bonds that result in entirely new products. When a chemical
reaction takes place there is a change in appearance, mass, volume and
The collision theory explains all there is to the rate of reaction.
The collision theory states that the rate of reaction depends on how
often and how hard the reacting particles collide. Reacting particles
need to collide with each other to be able to react. The more
collisions there are then the faster the rate of reaction will be.
The following methods of increasing the rate of reaction can be
explained by increasing the number of collisions between the reacting
* Temperature- When the temperature is increased in a reaction the
particles begin to move around much quicker. This means that when
they collide with each other they will collide harder.
* Catalyst- A catalyst works by giving the reacting particles a
surface to stick to on which they can collide with each other on.
This also increases the number of collisions between the
* Size- If one of the reactants is a solid it will have a smaller
surface area than...
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