Show MoreDecomposition of sodium thiosulphate
The aim or purpose of this investigation is to explain how concentration affects the rate of reaction (the decomposition of sodium thiosulphate in reaction with hydrochloric).
I will now give a simple definition of what rate of reaction actually is.
The rate of a chemical reaction is defined as the change in the concentration of one of the reactants or products in unit time.
I will now display my preliminary work.
I did a preliminary (trail) test to supply a source and to give a better perspective of the real experiment I am directed to carry out which is the decomposition of sodium thiosulphate.
The table below is a set of data collected from the…show more content…
In this experiment I have one independent variable which is:
• Concentration of hydrochloric acid (HCl).
• The temperature in the room may have altered.
A dependent variable is a variable you do not change during an experiment. Instead, it changes as a result of other changes you make.
The dependent variables in my experiment were:
• The rate of reaction.
• The volume of sodium thiosulphate.
The volume of sodium thiosulphate will remain unaffected throughout the whole experiment, Where as I will be changing the concentrations of hydrochloric acid. The volume of sodium thiosulphate will be 50cm³. The different concentrations of hydrochloric acid are 0.10M, 0.25M, 0.50M, 0.60M, 0.90M and 1.0M.
Now, I will discuss my prediction of what will happen during the experiment.
My prediction is,
• As I increase the concentration of hydrochloric acid and add it to the sodium thiosulphate the rate of reaction will decrease.
This happens because more particles are being added to the solution when the concentration increases. Therefore, this decreases the rate of reaction and the probability of a collision between reactant particles because there are more of them in the same volume and so increases the chance of a collision forming. This is where the collision theory starts in gases, increase in pressure means those molecules are closer together so there are more collisions.
Theory: Rate is the extent of the change that takes place
The Effects of Concentration on Reaction Rate with Sodium Thiosulphate
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The Effects of Concentration on Reaction Rate with Sodium Thiosulphate
In this experiment I shall be varying the volume of sodium
thiosulphate, hydrochloric acid and water, and measuring the reaction
rate. When I increase the amount of sodium thiosulphate with less
water, I think the time for the cross to disappear would be faster
than there would be with little sodium thiosulphate and more water –
taking in account the amount of hydrochloric acid is the same.
The reason why I think this is because the particles in the solution
that will collide. There is a theory called the collision theory, and
some of the factors from this, may affect the reaction rate in my
The first factor is the concentration. The concentration rate is
decided whether how strong the solution is. For an example, if there
is a lot of hydrochloric acid, and sodium thiosulphate, then there is
a high chance that the reactions will occur. If there is a solution
that is neutral, it would slow down the process of the reaction.
The second factor is the size of the particles. If there is a large
particle with a large surface area, and many small particles, the
smaller particles have a higher chance of colliding with the larger
particles. However, if there are small particles, and small particles
of another compound, then the reaction rate would be slower, because
the particles wouldn’t collide as easily as they would with particles
of a bigger size.
The third factor that affects collisions is the temperature. If there
is a higher temperature, then the particles are able to move freer and
faster, than they would if the temperature was lower. This means that
the reaction rate would be faster, because the collisions of the
particles are more frequent.
The fourth factor is to add a catalyst, but in this experiment we did
not add a catalyst.
Knowing the collision theory, it makes my predictions clearer with
what is going to happen when the experiment will take place.
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Reaction Rate Sodium Thiosulphate Collide Collisions Particle Compound Hydrochloric Acid
So, if I
have a large volume of sodium thiosulphate and hydrochloric acid, and
a small volume of water, then the concentration is high, and the
collisions would be more frequent, resulting that the reaction rate
would be fast. On the other hand if there was the opposite, and having
more water and less sodium thiosulphate, then the collisions would
occur less because the water is neutral and the process of the
reaction would be slower.
The equation for this reaction is:
[IMAGE]Hydrochloric + Sodium Sulphur + Sodium +
Sulphur + water
[IMAGE]2hCl (aq) + Na2S2O5 (aq) S (s) + 2NaCL (aq) +SO2
(g) + H2O (l)
To keep it a fair test
I will try to keep the experiment fair by the following:
· To carefully measure the exact amount of sodium thiosulphate, water
and the acid.
· To make sure the results are accurate, with stopping and starting
the stop clock
· To add the acid into the conical flask first, and the water, and
sodium thiosulphate at the same time, second.
· After each experiment I will clean the conical flask, so the results
can be fair.
While carrying out the experiment I will always need to think of them
points if I want to keep the experiment exact and accurate. If I
don’t, then the readings from the stop clock would be wrong, and there
would be a lot of anomalies. It is these anomalies that I should try
In this experiment, because I will be handling with liquids such as
acids which is an irritant, to get it in the eyes would be very
dangerous so you must always be wearing safety glasses, and to wash
your hands or any areas of the skin if you do get in contact with it.
You should always follow the rules that are found in the lab room.
They should be the regular rules that tell you to not run around the
lab, and to always wear safety glasses while carrying out an
experiment, and to not leave any items on the floor that you might
trip up on. Also, do not leave glass objects near the edge of the
table because they could easily roll on the floor and smash. Not
following these could be quite dangerous, so you must be careful at
· Measuring cylinder
· 50ml of sodium thiosulphate
· 40ml of water
· 30ml of hydrochloric acid
· A card with a cross in the centre
· A conical flask
· A stop clock
· Safety glasses
1. Measure 50ml of sodium thiosulphate in a flask, and 5ml of
hydrochloric acid in a different flask.
(Remember that the acid is an irritant, so be careful when measuring
it into the measuring cylinder, and always wear safety glasses.)
2. Place a conical flask on a piece of card with a cross on the
centre, and when you have finished pouring the liquids into the flask,
start the stop clock.
3. Measure the time it takes for the cross to disappear, and write it
down in a results table.
4. Do the experiment again, but this time change the volume of sodium
thiosulphate and water, but keeping the volume of hydrochloric acid
5. Each time you do the experiment again, make sure you clean the
conical flask. If it isn’t cleaned properly the results may not be
Hydrochloric Acid (ml)
From looking at the graph of my results table there is a slow increase
at first from the first experiment. There is a slow increase from the
second last reading of the first experiment. It goes from 73 seconds
to 189 seconds for the reaction. This is quite strange because of the
high difference so it must be an anomaly because on the graph a curve
doest fit the 3 last points together. This probably happened because I
didn’t clean the beaker properly, and there must have been remains of
water in the beaker. Or I did not measure out the water, sodium
thiosulphate or hydrochloric acid accurately. Because of this, the
line doesn’t fit the points on the graph that should look like a curve
and it means in the overall three experiments I carried out there was
only one anomaly.
In the third experiment what’s different from that one to the others
is that at the beginning there is a steep curve. This is because the
second point had a fast collision speed resulting in a fast reaction
speed like the first point. There is only a difference of 2 seconds.
My predictions that I had before I carried out the experiment match my
results. The reaction was faster when there was a small volume of
water, and more sodium thiosulphate and hydrochloric acid. This is
because of the particles that are colliding together. And as there was
more water than sodium thiosulphate, the rate of reaction was slower.
The result that I have provided from all three experiments does indeed
support my conclusion because there was only one anomaly in all three
of the experiments I carried out.
While carrying out all the experiments I think I had done quite well
in trying to keep the test fair. I did the experiment three times to
have a variety of results in case one of them had gone wrong or had a
lot of anomalies. There was however, one anomaly and it was from the
first experiment. I corrected my mistake, and the other two
experiments came out reasonably well.
To improve the experiment I think I could have had a preliminary
experiment, to give me a rough idea what would happen in the
experiment. That is also another reason why I carried it out three
times to give me a better idea.
To take the investigation further, I think I would have taken more
readings to show exactly the shape of the curve on the graph. Instead
of having 60ml, 50ml, 40ml etc, I would have 60ml, 55ml, 50ml, 45ml,
40ml etc. This would then give me 12 readings on a graph for three
experiments, and could help me see the exact shape of the curve near a
peak or dip.
There are a few advantages to doing this.
a. There would be more readings which would give better evidence to my
b. It should show a perfect curve in the graph if the experiment was
carried out correctly and accurately.
There are also a few disadvantages to doing this. And they are:
a. On the graph because there are more points it could look a little
b. The experiment would take longer to carry out.
Overall, I am quite happy with my results and the experiment that I
carried out, because it proves my prediction before the experiment and
it shows that knowing the collision theory, you can estimate what will
happen in an experiment.