However, the reaction rate between sodium thiosulphate and dilute hydrochloric acid can only be altered by changing the concentration or the temperature of the reactants.
The higher the concentration, the more collisions there will be. When the solution is more concentrated, there are more reactant particles between the water molecules. This makes collisions between the reactant particles a lot more probable. So, with more collisions happening, the quicker the reaction rate will be.
The rate will be measured by timing how long it takes for the cross to disappear and then using the equation
Reaction rate = ______1_____
Time
The reaction equation that is used is:
Na²S²O³ + HCL → NaCl + S + SO² + H²O
(aq) (aq) (s) (g) (l)
Equipment
Sodium thiosulphate
Hydrochloric acid
Water
Burette
2 beakers
Conical flask
Stopwatch
Method
- Using a burette, measure out 50cm³ sodium thiosulphate into a conical flask and 5cm³ of hydrochloric acid into a beaker
- Place conical mask over a black marked cross, and then pour hydrochloric acid into the flask.
- Once all the acid is in, start the stopwatch while looking down on the flask at the cross. When the cross disappears, note time
- Repeat experiment another 8 times with different concentrations of sodium thiosulphate by going down in fives. Add water to make up to the 50cm³
Affecting factors
If the measuring device used is not that accurate, then the experiment will not be that accurate either as the exact amounts of each solution may not be used. This could affect the experiment as it would end up changing the concentration of the solution, resulting in either a quicker or slower time. This means that if there are more reactant particles between the water molecules these would make collisions between the reactant particles a lot more probable, and vice versa. Due to this, I will use a burette for accuracy in measuring.
If the temperatures of the solutions change, then this could affect the rate of reaction, resulting in different times and a quicker reaction. When the temperature is increased the particles will have more energy and therefore move faster. Consequently they will collide more often. Particles with more energy are more likely to overcome the activation energy barrier to reaction and hence react effectively
Also, once the cross has disappeared, it is hard to stop the stopwatch at the precise moment, which could make the time off by a few seconds.
For my results I am planning to get a good range of concentrations, from 1.0-0.2, thus making my graphs more accurate and enabling me to get a better analyse and evaluation. I will time how long it takes for the cross to disappear, and then I will find the reaction rate from this. I will repeat any anomalies that appear in my results to make my overall results more reliable.
ANALYSING
Results:
The experiment with the concentration of sodium thiosulphate at 0.9 was redone, as the first result was an anomaly and did not fit in with the rest of the results.
Original:
From doing this experiment I have found out that as the concentration increases, the time for the reaction to occur decreases, so they are inversely proportional. This means that the rate of reaction is increasing. In the experiment, the time increased with less concentrated solution by about 3secs, but as the solution became weaker and weaker the time lowed down a lot.
Conclusion
From the graph I can see from using the live of best fit that there is a positive correlation. This shows that they are directly proportional. However, the curve in the graph is not that steep, showing that the decrease in time taken for the reaction is not that rapid. The two chemicals react together to form a yellow precipitate of sulphur.
Chemical reaction taken place:
Na²S²O³ + HCL → NaCl + S + SO² + H²O
(aq) (aq) (s) (g) (l)
Time against concentration
Concentration against rate of reaction
This graph is plotted rate of reaction against concentration of sodium thiosulphate. It shows that concentration is directly proportional to rate of reaction. This proves that particles have to collide for a reaction to take place. If the concentration of a solution increases, then the likelihood of collisions between the reacting particles is higher, resulting in a higher reaction rate.
If two or more molecules collide but are not orientated correctly then no reaction will take place.
My results support my prediction. When the temperature is constant for all the experiments carried out, the rate of reaction is directly proportional to the concentration. They match my prediction by increasing the rate of reaction as the concentration gets higher.
EVALUATING
I think that my experiment has worked out well as I was able to attain good results that supported my prediction, and resulted in being able to have a good set of graphs with the correct correlation. Also, any anomalies that I had were repeated, so as to make my results more accurate.
My results were accurate enough to use as I measured the solutions using a burette, making it more precise and therefore reliable. Also, the same equipment was used, and the temperature was the same for each experiment, meaning that this factor did not effect or change the results.
To improve my experiment if I redid it, I would use a light sensor. The light sensor would pass through the flask to a receiver. At the point when no light can reach the receiver, then the time will be stopped. This is a lot more accurate, compared to trying to judge using the naked eye.
I think that my method was quite precise and resulted in getting the best results possible with the equipment that was available to use. The measuring devices were accurate. An improvement to the method would have been to have done more repeats to make sure that my results were correct.
One result that did not seem to fit the overall results was when the concentration was 0.9. The time increased by about 5secs, instead of just around 3secs, resulting in an anomaly in the results. This could have been caused either by using sodium thiosulphate from a different burette which would have a different temperature or maybe just human error and not stopping the stopwatch and the correct time.
An experiment that could be done to extend the work would be to find out the effect temperature has on the reaction rate between dilute hydrochloric acid and sodium thiosulphate. This would be able to show which one has the larger effect of the reaction rate.
