Max Barlow
Rates Of Reaction Coursework
Introduction
What is Rate of Reaction?
The Rate of a reaction tells us how quickly a chemical reaction happens.
Fast reactions, like dynamite exploding start and finish within a fraction
of a second. Slow reactions like concrete setting, may take days, weeks or
even years to finish. During a reaction we can measure how much
reactant is used up in a certain time.
Aim
In this coursework I plan to investigate the effect of varying the
temperature of sodium thiosulphate on the rate of reaction between
dilute sodium thiosulphate Solution (ST), Hydrochloric Acid (HCL). The
symbol equation for this reaction is:
2HCl(aq)+Na2S2O3(aq)
2NaCl(aq)+SO2(g)+S(s) + H2O(l)
Hypothesis
There are many factors that can affect the rate of a reaction. These
factors consist of the concentration of particles, the temperature of the
reactants and the surface area. In my experiment I will vary the
temperatures of the reactants and keep all other factors constant to the
best of my ability. Changes in temperature can affect the rate of reaction
because the more heat that is applied the particles will have greater
energy and cause more collisions. When a collision happens the two
particles that have collided cause a reaction to occur. However these
particles must have enough energy to break down existing bonds the
particles have. This is why I have predicted the rate of a reaction is when
‘The higher the temperature of sodium Thiosulphate the faster the
reaction’.
Background Information / Scientific Theory
The rate of reaction should increase when the temperature increases or a
chemical substance is added that is very reactive. This is due to a theory
called the collision theory. A reaction can only occur when the particles
collide with enough energy to break existing bonds. A chemical change
can only take place with a fixed amount of collisions by the particles.
These are often referred to as successful collisions. The successful
collisions have a sufficient amount of energy at the moment of impact,
causing existing bonds to break to form new bonds. By rising the
temperature or chemical substance is added that is very reactive, more
collisions would happen and therefore more successful collisions, which
will increase the rate of reaction. According to the Collision Theory, the
average kinetic energy of the reactant molecules should increases, and
this should increase the impact energy upon collision.
The following diagrams show what happens to the particles when sodium
Thiosulphate is added to hydrochloric acid.
Lower temperature
Higher temperature
Increasing the temperature of a substance in solution means that the
particles of that substance have a greater energy. In the reaction between
sodium Thiosulphate solution and dilute hydrochloric acid
Hydrochloric acid + sodium thiosulphate
dioxide + sulphur + water.
2HCl(aq) + Na2S2O3(aq)
H2O(l)
2NaCl(aq)
sodium chloride + sulphur
+
SO2(g)
+
S(s) +
solid sulphur (S(s)) is formed in the flask. Increasing the concentration of
sodium Thiosulphate means that the solid sulphur will be produced
more quickly and there will be less time before the cross can no longer be
seen.
When making different concentrations of sodium Thiosulphate and
hydrochloric acid I will take care to use the same volume of both
substances and only vary the temperature of the sodium thoisulphate. If
I did happen to use a greater volume for one of the temperatures I was
measureing the cross under the beaker would disspaere quicker than it
should of.
There are different variables, which can be tested for this experiment.
These include:
Surface Area – Surface area is a measurement of how much surface is
exposed. As the surface area is being increased, the rate of the reaction
is also being increased. We find that small pieces of solids, especially
powders, react faster than large pieces because they have a larger
surface area than a solid.
Concentration – The acid particles can only react with the marble chips
when they collide. As you increase the concentration of the acid, there
are more acid particles in the same volume. Therefore, there is a greater
chance of acid particles colliding and reacting, with the particles on the
surface on the marble. However when the acid is diluted, there are fewer
particles within the volume of the water and the reaction tends to be a lot
slower.
Catalyst – A catalyst is a substance which helps to speeds up a chemical
reaction. At the end of the reaction, the catalyst is chemically
unchanged. Before the reactant can turn into products they need enough
energy to start off the reaction. The energy needed to start a reaction is
called its activation energy. A catalyst lowers the activation energy. With
a catalyst a lot more particles have enough energy to react.
For this experiment I will be testing the variable Temperature and how it
affects the rate of reaction between Sodium Thiosulphate and
Hydrochloric Acid.
Fair test
To assure that the experiment we carry out will be a fair test, a number
of procedures must be carried out first.
The most factors that need to remain constant are listed below.
Volume of solutions - Both solutions need to be the same to ensure that
the results we gain are fair. If the volumes are not the same the results
that we will obtain might turn out to be anomalous results. Also if we
accidentally use less solution in the beaker, it will also affect the results
in a way as the reaction would be quicker.
Repetition - The experiment should be followed out at least twice to
ensure we get accurate and fair results. By repeating the experiment
twice we can calculate a mean result and see if there are any patterns or
anomalous readings in our results. By using an average, we could make
other judgments about how well the experiment went. If I obtain any
obvious anomalous results I will discount them when working out the
mean, and analyze why I obtained that result in my evaluation.
Heat- I will vary this and use different temperatures and use valuse of
10, 20, 30, 40 and 50 degrees celcius.
Preliminary Work
Preliminary work was carried out before the experiment to determine the
temperatures and measurements that will be used for the final
experiment. It also allows us to see how much of each reactant that will
be needed and also to gain a perspective on it.
Aim
To decide on the factors I intend to use in my preliminary work:
Investigate the effect of varying the temperature on the rate of reaction
between dilute Sodium Thiosulphate Solution (ST), Hydrochloric Acid
(HCL).
Prediction
By using my background knowledge, scientific theory and my
preliminary work I predict that the higher the temperature of the sodium
thiosulphate, the faster the reaction will be.
In my background information it says:
‘Increasing the temperature of a substance in solution means that there
will be more collisions of that substance. This means that the particles
collide more frequently with each other and the rate of the reaction
increases.’
This will prove my hypothesis and try to help me in the test.
Safety
Be careful when dealing with the Hydrochloric Acid as it is an irritant
and harms the skin.
Lab coats should be worn to protect clothing.
Wear goggles.
Generally, care should also be taken when using the Sodium
Thiosulphate
Don’t breathe in gases, keep the room well ventilated.
Equipment
The equipment needed for the preliminary experiment is the following:
. Conical flask.
This is what we use to pour the substance into.
. Sodium Thiosulphate.
This is one of the reactants we use.
. Hydrochloric acid.
This is one of the reactants we use.
. Tile with ‘X’ on it.
When the X disappears from view we will stop the stopwatch.
. Stopwatch to time the rate of reaction.
. Beaker.
This is to pour the chemicals into the conical flask.
. Measuring Cylinder
This is to pour the chemicals into the beaker.
.Water bath.
This is to change the temperatures of the reactants.
Diagram and setup
Tile with a
cross marked
on it.
Sodium Thiosulphate
solution
Method
.Set up the apparatus as shown above.
.Mark an “X” on the tile which the conical flask would be placed on top.
.In the beaker pour 50ml of sodium thiosulphate that has been heated to
10 degrees celcius.
.Start the timer as soon as all the HCL has been poured in.
.Wait to see how long it takes for the ‘x’ marked on the tile beneath the
beaker to no longer become visible.
.Once the ‘x’ is unable to be seen by the observer, stop the watch.
.Wash out the beaker.
Repeat steps but change the temperature of sodium thiosulphate to
required amount.
Results
Temperature
1st test (secs)
10
20
30
40
50
25.34
20.44
16.22
11.73
7.35
2nd test
(secs)
24.93
20.35
15.43
12.01
8.12
3rd test (secs) Average
25.12
20.52
23.98
11.97
7.5
25.13
20.44
15.83
11.9
7.66
Correlation between the time it took for
the cross to dissapear against the
temperature of the reactants.
Time take for cross
to dissapear
30
25
20
15
10
5
0
0
10
20
30
40
50
Temperature of reactants (degrees celcius)
60
Conclusion
I can conclude to say that my hypothesis, which was:
‘The higher the temperature of sodium Thiosulphate the faster the
reaction will be’.
Was proven correctly by the results I have obtained. As you can see in
my prediction I said that the higher the temperature of sodium
Thiosulphate the faster the reaction would be was true because
Increasing the temperature of a substance in solution means that there
will be more collisions between the two reactants. This means that the
particles collide more frequently with each other and the rate of the
reaction increases. Also you can see on my graph the line of best fit has
dissected most points meaning the hypothesis was proven correctly.
My hypothesis was correct also there were hardly any anomalies only
once when the time increased and had taken even longer than normal
but this was probably a matter of wrong measurements or wrong timing
when we added the chemicals. When working out the average time taken
for that temperature I disocuted the anomolie as it was clearly inacurate
and would have affected my graph.
Evaluation
Overall, I feel that the experiment was a success. The results were
constant with only one anomaly. This may have occurred from
inaccurate measuring or the volume of one of the reactants having the
wrong measurement. I am glad that we repeated the experiment three
times as it allowed me to gain a mean reading of the results obtained and
it also enabled us to check the accuracy of our results.
To expand our experiment and to continue it further, I believe that we
could have tested other factors and to see how the other variables may
affect the rate of the reaction while using the same reactants. The
method would be similar but would be adapted slightly depending on the
factor that I changed. I think that by testing these variables my scientific
knowledge would be expanded and would give me more detail to analyse.
The changes that could be made to this experiment to improve accuracy
of results are:
The results could be done more then 3 times so that there would be less
of a chance of using incorrect results then doing them as I did.
Also if I were to do this experiment again I would prefer to use a beam of
light instead of a cross. I would then measure when the beam of light has
disappeared by using a light meter. This would give me far more accurate
results as observing weather the cross had disappeared with my eyes
was extremely subjective and open to doubt. Whereas using a light meter
would remain a constant and objective.
Over all I believe that this experiment was a success because it gave me
constant accurate results. However I would like to repeat the experiment
with the changes that I have suggested and compare results to see if
there would be any difference.