For my practical I will be using a burette and pipette to measure out the liquids because they are far more accurate and I will use a light gate connected to a computer to record the time taken for sulphur to form because once again it will be a lot more accurate.
Diagram:
Method:
I will use the following concentrations of sodium thiosulphate in my practical:
I will set up 2 burettes, one full with Sodium thiosulphate and one full with distilled water, up on 2 stands. On the third stand I will position a light gate that is connected up to a computer. Once I have done this, I will be able to fill a conical flask as accurately as possible with the needed amounts of water and sodium thiosulphate. I can then measure out 5cm³ 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.
As I increase concentration, the reaction rate should increase accordingly because if I double concentration, there are twice as many particles of sodium thiosulphate in the same volume of acid making a collision, a successful collision, more likely to occur. A successful collision is one in which bonds are broken, I.e. The collisions take place with enough energy to overcome the activation energy needed to break the bonds.
Results:
Safety:
- Ties and Shirts tucked in
- Stools cleared from gangway
- Safety Goggles worn at all times
- Spills mopped up promptly
- School bags left outside
Observation:
From my graph I can say that reaction rate and concentration are directly proportional. As one increases, the other increases accordingly. As we double concentration, reaction rate doubles. If we increase concentration, we increase the number of particles in the same amount of solution so we therefore increase the chance of a successful collision. A successful collision is one in which bonds are broken i.e. collisions with enough energy to overcome the required activation energy.
Conclusion:
There were many sources of error in my experiment. The main source of error was eyesight. No matter how ever accurate the burette and pipette were, they still relied upon my eyesight for the final word. 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.
