The calculations to find out the new molarity are:
Original molarity x volume of thio = 0.2 x 16
Total volume 20
Prediction
I think that when I decrease the concentration of sodium thiosulphate, the rate of reaction will decrease and the time it takes to precipitate will increase. This is because when the concentration is decreased there are fewer molecules to collide with the hydrochloric acid molecules so the reaction will be slower.
Results
Experiment 1
Experiment 2
Conclusion
From my results and graph I can see that as the majority of the sodium thiosulphate decreases the time increases. I can also see that the rate is proportional to Molarity. My Molarity/time graph goes down in a gradually increasing curve. This is slightly strange because it should be a steady curve and the difference between times increases too much towards the end. This tells me that my results could be slightly inaccurate. These results tell me that as the sodium thiosulphate concentration decreases the time increases. This is because as the sodium thiosulphate is diluted, there are fewer particles to collide with hydrochloric acid particles. Fewer collisions mean a slower reaction because the particles are taking longer to collide with each other. This is because there are also water particles in the way. Therefore as the sodium thiosulphate is diluted more water is added (the number of water particles increase) causing the reaction to be slower and take longer.
My results do agree with my prediction because I said that the rate of reaction will decrease and the time will increase. This is what happened so my prediction was correct. The reasoning in my prediction is justified by my results.
As my molarity increases the time gets quicker by small intervals at first, then progressively bigger intervals. I think if I diluted the sodium thiosulphate even more than we did in this experiment then the intervals would increase even more.
The calculations I used to reach my conclusion are working out the new molarity and taking the average out of two tests.
Evaluation
In my experiment there were a couple of parts that weren’t exactly fair and accurate. Each time I shook the beaker, it may have not been the same vigorousness each time. Also, whilst shaking you can’t see whether it’s gone opaque so you have to stop every now and again to see. Each time I may have stopped at different times so this wasn’t completely accurate. Also, I timed it using the wall clock and this isn’t as accurate as using a stop clock. Also, some of the chemicals each time may have been left in the measuring cylinder.
All my results do agree, and none of them look wrong. They all follow a sort of pattern so I think they are all sensible results.
My results are quite reliable and accurate because all the faults in my method occurred with each experiment so they all were fair to each other. However, the problems above might mean that my results aren’t as reliable and accurate as they could be.
I think my results that aren’t exactly fitting into the pattern may have occurred because of the slight inaccuracy in my equipment.
I think my results are good enough though to make a valid conclusion because you can see a difference and patterns in my results as the molarity increases. Also, I kept everything except the sodium thiosulphate the same each time so it was as fair as I could make it.