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Plan an experiment to investigate the effect of changing the concentration of sodium thiosulphate on the reaction between hydrochloric acid and sodium thiosulphate.

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Plan an experiment to investigate the effect of changing the concentration of sodium thiosulphate on the reaction between hydrochloric acid and sodium thiosulphate. Apparatus: 1 conical flask 2 burettes 1 pipette Light gate/computer Sodium Thiosulphate Hydrochloric acid Distilled water Safety Goggles 3 stands From my preliminary experiment I have a basic idea of what the results will be like. As concentration rises, reaction rate should rise accordingly. In my preliminary experiment I varied the concentration as follows. Sodium Thiosulphate (cm�) Water (cm�) Concentration (g/dm�) Time (s) Reaction Rate (1/s) 50 0 40 37 1/37 40 10 4/5 x 40 = 32 47 1/47 30 20 3/5 x 40 = 24 68 1/68 20 30 2/5 x 40 = 16 108 1/108 10 40 1/5 x 40 = 8 320 1/320 I put 5cm� of hydrochloric acid in a conical flask and then put in 50cm� of dilute sodium thiosulphate in as well. I swirled the flask and placed it on a piece of paper marked with a cross, meanwhile starting the stop clock. ...read more.


I can then measure out 5cm� of hydrochloric acid using a pipette. Once the light gate is positioned around the conical flask, I can put in the hydrochloric acid and sodium thiosulphate, swirl them around and turn on the light gate. When enough sulphur has formed (when the cross disappeared in the preliminaries) the light gate will sense this and record the time. Once I have this time I can record it and continue to do the experiment with all the other concentrations and repeat each one three times for reliability. To make the test as fair as possible I will only vary one variable, keeping the rest constant. I will vary the concentration of the sodium thiosulphate only keeping the concentration of the hydrochloric acid, volume of dilute sodium thiosulphate, volume of hydrochloric acid, and temperature the same. I will also wash the conical flask after each experiment to make sure that I tried my hardest to stop it from getting contaminated and altering the results in any way. ...read more.


One of the main parts of the experiment, the end of the reaction, was also judged by my eye. I was unable to use a light gate as I had requested, which would've have been far more accurate as it would've stopped the clock at a near enough time for each concentration. I also had to use a measuring cylinder instead of a pipette to measure out the hydrochloric acid. I tried to keep the experiments as fair as possible by washing out the conical flasks each time and trying to stop the clock at roughly the same point each time. To make my experiment more accurate, I could repeat it using a light gate and using more accurate apparatus such as a pipette instead of a measuring cylinder. I could also use a new conical flask each time instead of rinsing the previous one out and re-using it. These results are far more reliable than in my preliminary experiment as I repeated the procedure three times in this experiment. Overall I think I conducted the experiment quite well by trying to keep all other variables apart from concentration constant. ...read more.

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