An experiment to investigate the effect of changing the concentration
of hydrochloric acid on the rate of reaction with sodium thiosulpahte.
I am trying to find out how the concentration of hydrochloric acid
affects the reaction time with sodium thiosulpahte.
If a clear solution of sodium thiosulphate is mixed with hydrochloric
acid then a reaction will occur where a creamy-yellow precipitate of
sulphur is produced.
Text Box: + Text Box: + Text Box: + Na2S203 2HCL
Text Box: + 2NaCl SO2 S
The sulphur takes a while to form and starts to turn the water cloudy
after a short time. You cannot tell when the reaction has stopped so a
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Everyone should behave sensibly to prevent accidents.
The rate of reaction depends on how often and how hard the reacting
particles collide with each other. The particles have to collide hard
enough in order to react. The rate of reaction can be increased by
increasing the temperature, making the solution more concentrated,
size of solid particles and by adding a catalyst. They all increase
the number of collisions.
* To make this a fair test I will only change one variable.
* Each experiment will be done three times so an average can be
* The same equipment will be used in each experiment.
· Measure out 50ml of thiosulphate and add it to the conical flask.
· Draw a cross on a piece of paper and place the conical flask on it.
· Measure out 10ml of acid and add it to the conical flask and start
· Look into the top of the conical flask and when the cross can no
longer be seen stop the stop watch.
· Do the experiment again but measure out 8ml of hydrochloric acid.
Then add 2ml of distilled water. The ratio for each experiment will
therefore be 10:0, 8:2, 6:4, 4:6 and of acid to water
I conclude that whilst carrying out this investigation I found out
that the more acid was in the solution the cross on the paper
disappeared quicker. This shows that the more concentrated the acid is
then the quicker the reaction time. My research about the collision
theory was correct and the more concentrated the solution is then the
number of collisions will be increased. If the numbers of collisions
are increased then the reaction time will also be increased.
My prediction 'that the less concentrated the acid is then the longer
it will take for the sodium thiosulphate to react with the acid' is
correct because experiment number 5 with the least amount of acid in
the solution took the longest time to stop reacting (the cross to
disappear) and had a rate of reaction of 0.21 (x10) which is the
lowest. All my results supported my original prediction.
I cannot rely entirely on the results of my experiment as it wasn't
carried out with a high level of accuracy, but...