Investigating The Rate Of Reaction Between Sodium
Thiosulphate And Hydrochloric Acid Essay, Research Paper
Investigating the rate of reaction between Sodium
Thiosulphate and Hydrochloric Acid Diagram
Aim : We did 4 experiments to find out how
the rate of reaction changes with differing concentrations of Sodium
Thiosulphate, Hydrochloric Acid and water. As an inert and stable liquid, water
was used to alter concentration of Sodium Thiosulphate without changing the end
amount of solution. All the atoms in a water molecule have a full outer shell,
so they would not react with the other chemicals.Equipment
???? Beakers, ??????????????????????? Measuring cylinders Clamp stand and Clamps ??????????????????????? Black paper tube ??????????????????????? Light probe and Blue box ??????????????????????? Datalogger ??????????????????????? Lamp ??????????????????????? Total of 30cm3 H 0,50cm3 Na S O , 12cm3 HClMethod : We wanted to change the concentration
of Sodium Thiosulphate and Hydrochloric Acid, but without changing the overall
quantities. To do this, the Sodium Thiosulphate and water were mixed at
different ratios, with always a constant amount of acid. The table below shows
the 4 different experiments, and what each solution composed of. The ?Graph?
column relates to the graphs taken from the Datalogger for that experiment,
which are included at the back of this piece. Sodium
Thio-sulphate (cm3) Water
(cm3) Hydrochloric
Acid (cm3) Graph
number 20 0 3 DPPAS_02 15 5 3 DPPAS_03 10 10 3 DPPAS_04 5 15 3 DPPAS_05 ? ??????????? We did not do the experiment in
which 0cm3 Sodium Thiosulphate and 20cm3 water were used, as there would have
been no reaction. In total, there were always 20cm3 of water and Sodium
Thiosulphate, with 3cm3 Hydrochloric Acid, giving a total solution of 23cm3 ??????????? The black tube was put around and
below the beaker to help prevent any unwanted light from entering the light
probe, as this would have impaired our results. The reason we used a Datalogger and light
probe instead of the old ?cross? method, is threefold. First, human error. The
cross would not just disappear ? it would fade. There would be no specific
point at which the cross would disappear, and the results of your experiment
would be based entirely on a person?s eyesight. Second, this method will only
tell you (albeit inaccurately) when the cross disappeared, i.e. how long it
took for the reaction to get to a certain point of cloudiness. It would not
tell you the varying rates of the reaction. You would not be able to tell if
the reaction speeded up, slowed down, went steady all the way e.t.c. Lastly,
what would you do if the reaction never got as far as making the cross
disappear? Or what if the reaction took a number of hours to get that far? This
traditional method is about as accurate as taking the temperature from a beaker
of water with your finger. To do the experiment, we set up the
apparatus as explained above. We put the various amounts of chemicals into the
beaker, and used the Datalogger and blue box to record the first 3 minutes of
the experiment, and then used the computer to draw up a graph. The blue box was
set to SLOW
and 10k lux.Prediction : I predict that the rate of reaction
will increase (and get more cloudy, more quickly) when the solution of Sodium
Thiosulphate and Hydrochloric Acid are strongest, and there is no water. The
reason for this is that it will be easier for the Sodium Thiosulphate to react
with the Hydrochloric Acid, as they are the only two chemicals in the beaker,
and there is not water to hinder the rate of the reaction. There will also be more Sodium Thiosulphate to react with
the Hydrochloric Acid, regardless of how much water there is.Results : The graphs from the Datalogger are
included in this project. The filename of each graph correspond to the
filenames (DPPAS_xx) listed in the table above. The table below shows the
amount of time that each graph took to level out, i.e. how long the experiment
took to finish. To work out the rate of reaction over the whole reaction (up to
the point where the reaction levelled), I divided the light depreciation (k
lux) by the time taken (minutes) to give a rate of k lux/min. Light
depreciation is k lux at start minus k lux at end of reaction. Here are the
results: Graph Reaction
Finished in k lux at start k lux at end k lux dep./s DPPAS_02 70s 8.9 2.1 .097 DPPAS_03 80s 8.9 2.7 .078 DPPAS_04 100s 8.4 3.2 .052 DPPAS_05 N/A 8.3 N/A N/A ??????????? Analysis
/ Conclusion : Our
results show that, as predicted, the more concentrated solutions reacted more
quickly than the weaker ones. As the concentration got weaker, the reaction was
slower. I would expect the same pattern of you swapped Sodium Thiosulphate and
Hydrochloric Acid for two other chemicals, which are not affected by water, but
will react with each other. There were a few anomalies at the beginning of two of
our graphs, but the end results were all in proportion. The experiment shown in
DPPAS_02 twice as concentrated as the experiment in DPPAS_04. In theory, this
means that the light depreciation was twice as much. 0.052 times two is 0.104,
which is very close to the result we got of 0.097. This is assuming that the
result of 0.052 was correct. Giving leeway for inaccuracies, this was as good a
correlation as we could have expected ? only 0.008 k lux inaccurate. Also, as
you can see from the k lux/sec depreciation rate, I was not able to write up
figures for the last experiment. This was because, in the time we recorded the
experiment for, the chemicals never stopped reacting. As with most of the
graphs we never, for some reason, recorded a full 3m (all our graphs finished
at between 2m45s and 2m55s). This didn?t really matter, as all the other graphs
levelled out within the time recorded. But we stopped recording DPPAS_05 before
the reaction stopped, and as a result were not able to work out a finishing
time, and thus an overall rate of reaction. For this reason, I did not think it
fair to put in the results we got from the partial experiment into the main
table above. We can still however work out a rate for the amount of the
experiment that we did. Start light of 8.3, minus finish light of 4.6 is 3.7,
divided by time, which is 165, equals 0.022 k lux dep./s. Assuming this is the rate of reaction throughout the experiment, we
could times this number by four (as DPPAS_05 was four times weaker than
DPPAS_02), and end up with 0.088, which is only 0.009 k lux dep./s out. So by
correlation these three rates of reaction against concentration, we can see
that the results are related, and that the experiment worked well.? Evaluation : In all, our experiment worked quite
well. We did come across a few problems with accuracy though. One of the most
significant one was that the Dataloggers are not 100% accurate, and do not give
very detailed readings So when you take results into account, you have to give
some leeway for the inaccuracy of the Datalogger. ??????????? On DPPAS_05, we had a huge anomaly,
of nearly 4 k lux. This appeared about 20s into our experiment (according to
our graph). We have no idea how or why this happened. My best guess is that
somebody knocked the experiment and/or the Datalogger whilst it was recording. ??????????? I would do many things to improve
the experiment if I did it again in the future. Firstly, I would leave the
experiment for a long time (at least an hour) so that all the experiments would
finish. Second, I would do the experiment in a darkroom, and make the tube
extend upwards as well so that it covered the lamp, and all the light coming
out of the lamp would go through the beaker. If I could, I would also use a
more expensive and better quality Datalogger that could record the light more
precisely and accurately, but this would prove impractical for just one
experiment. ??????????? One thing I would be hard pushed to
overcome would be the light that passes down through the glass sides of the
beaker, via TIR. This is however not that important, as any light entering the
light sensor via this route would remain constant.