Conical flask, hydrochloric acid (5cm3), paper with cross on, stopwatch, sodium thiosulphate, water, 2 measuring cylinders (10 & 50 cm3), thermometer.
Trial Run
Aim: to find the minimum and maximum concertration.
Set up apparatus as shown.
Results
Conclusion
Maximum concentration of sodium thiosulphate: 50 cm3
Minimum concentration of sodium thiosulphate: 10 cm3
Temperature: 19 Celsius
The trial run showed me that if you increase the concentration of sodium thiosulphate past 50 cm3 it is hard to stop the stop clock in time because the reaction is to quick to time. If you drop the concentration past 10 cm3 the reaction takes to long to time.
Experiment
Method
Set up apparatus as shown. Measure 50cm3 of sodium thiosuiphate accurately in a measuring cylinder. Put it into a conical flask. Put the conical flask onto the cross. Measure 5cm3 of hydrochloric acid accurately in a different measuring cylinder so the reaction does not take place in the cylinder. Measure the temperature. Put the acid to the conical flask and start the stopwatch. Stop the stopwatch when the cross disappears. Put the results into a table. Repeat the experiment, change the concentration of the sodium thiosulphate, and keep the temperature the same. Do the whole
Experiment twice.
Fair test
To make it a fair test I will keep the following variables the same: 5cm of Hydrochloric acid, total volume, heat. It is important to keep the amount of hydrochloric acid because it may alter the rate of the reaction. It is important to keep the temperature the same because the more heat a reaction gets the more kinetic energy it will have so the reaction rate will increase.
Independent variables - concertration of sodium thiosulphate.
Dependent variables - rate of reaction, time taken
Safety
Handle everything with care, wash hands if acid is spilt on skin, wear goggles.
Results
See graph sheet for graphs
Conclusion
As the concentration of sodium thiosulphate increases the rate the cross disappears increases. This is because when the concentration of sodium thiosulphate is increased there is more sodium thiosulphate particles to collide sucsesfully with the acid to cause a reaction thus rate of reaction is increased as shown by my graphs, as the concertration increases show does the time. 1\time graph shows the volume of sodium thiosulphate is directly proportional to the speed of the reaction. As you double the volume of sodium thiosulphate the reat of reaction of reaction doubles.e.g. 10 times 2 = 20, 0.05 times 2 = 0.1
Evaluation
To improve my reasults I would take some more readings between 20 - 10 cm3 concertration of sodium thiosulphate because there is a big gap in my reasults.
I would extend my investigation I would use different pH of acid and keep the concertration of sodium thiosulphate the same.
