First I will get all the solutions I would need for this experiment like Sodium Thiosulphate and Hydrochloric Acid, so I don’t waste my time looking for it afterwards. Then I would get all the apparatus, which is required for the experiment like conical flask, measuring cylinder and test tubes. I will also have my safety goggles on me just incase something might happen. Next I will measure the amounts of each of the solutions.
As you can see I am going to keep Hydrochloric Acid at constant volume but change the amounts of Sodium Thiosulphate, which will change the concentration level of solution. I am going to repeat the whole of the experiment in total 3 times and record the results in a table. I will draw a cross on a piece of paper and will put conical flask on top of it and then see how long it takes for it to disappear. The reaction that I am expecting to happen is for the solution to produce a yellow suspension of Sulphur, which after some time will make the mixture opaque. As soon as I'll put the last drops into the reaction I will start the stop – clock, and as soon as the cross wont be seen I will stop it. I will be looking at it from the top, because that would be the easiest way to see the cross on the bottom of the flask. Then I will record the time. After I have done that I would be able to plot the graph.
After my graph was drawn I would be able to see whether the concentration was proportional or not.
CONICAL NA S O
FLASK
SAFETY Measuring
GOGGLES Cylinders
Results
From this set of results I can plot a graph and calculate the average of the three. On the first set of results the time on the third run didn’t go according to the prediction so we had to repeat this one again. When we had re done it having it set up according with the right amounts for that particular run, the result we achieved fitted the pattern. Then I used the correct result to plot on the graph. When I have plotted all the points on graph paper I could see how fast the rate of reaction had gone and which one was faster on what set of results. From the graph I could see that the third set of results was a lot slower than the first two. I think that was because I did it on another day and it was colder in the room because it was first thing in the morning. So the room wasn’t as warm comparing to the last lesson of the day before, when lots of students were there all day. As you can see temperature is very important when doing an experiment, as it changes a lots of things for you.
After plotting the 3 sets of results I calculated the average and plotted that on a different graph and that showed me the overall rate of reaction.
From my graph I was able to tell that the rate of reaction was reasonably fast and followed the prediction of being faster at the start because the mixture wasn’t as diluted and a lot slower by the end of it, when most of the mixture was water which is very un-reactive.
Conclusion
From the graph it can be seen that as the volume of Sodium Thiosulphate decreases i.e. the concentration of Na S O decreases, the time taken for the reaction increases, which means that the rate of reaction decreases. My prediction was correct as this is exactly what I said would happen, because as we increased molarities we increased the collision effect and the rate of reaction with it.
Now since rate of reaction is amount of sulphur produced divided by time then, if the amount of sulphur stays the same i.e. enough to produce the colour change then the rate of reaction can be judged by taking values of 1/time.
Since the amount of sulphur is same in each experiment ( i.e. the amount needed to make a clear colour to cloudy) then
Rate of Reaction = Constant / Time Taken
Rate of reaction is proportional to the recepireal of the time taken. Therefore a graph can be drawn of rate of reaction (1/time taken) against concentration ( judged by volume of Sodium Thiosulphate).
Concentration of Volume of Na S O
Sodium Thiosulphate Total Volume of Solution
Total volume is always 40 cm , so it has a constant volume. Therefore concentration of Sodium Thiosulphate is the volume of
Na S O
Constant
So concentration of Sodium Thiosluphate is proportional to the volume of Sodium Thiosulphate. If you double the volume of Na S O you double the concentration of Na S O .
Therefore on a graph we can plot the points of 1/time against the concentration of Sodium Thiosulphate.
Results for 1/ Time
From these calculations I am now able to plot them up on a graph.
From the graph I can see that the concentrations is proportional to the 1/ Time, but not directly as not all points are on the line, even though they do follow the pattern I predicted. On each set of results there are only 2 or 3 points out of line out of the 6 runs, so I can see it isn’t completely wrong.
Now that I have plotted the 3 sets I can obtain an average by calculating the times of 1/ Time, adding and dividing them by 3.
Now that I have plotted these results on the graph I am able to observe the pattern. From the graph it can be seen that the rate of reaction judged by 1/ Time, is proportional to the concentration of Sodium Thiosulphate judged by volume of Sodium Thiosulphate.
Evaluation
The graph shows that the points were all very close together even though there are only two that are actually on the line. I still think the rate of reaction was proportional to the concentration of Sodium Thiosulphate. I have taken six readings which was meant to make it more accurate but I don’t think it did that at all. If I could do the experiment again I would repeat most of my runs, to see whether it would have gotten me a different and better set of results. There can be a number of reasons for this, which I am going to explain next.
We didn’t stir our mixture at all maybe if we had done the results would have been a bit more different. I also think that when we were timing it we didn’t do it with enough accuracy. My partner might have started the stop clock earlier or stopped it sooner and even maybe later. So the time would have made the biggest difference and would have been the biggest cause of the points not being completely in tune with the line of proportion. The other thing that made a big difference to the results would have been temperature. As we didn’t have enough time to finish all the experiments in one lesson we had to do ours in the next. When we repeated the experiment the next day, the first lesson of the day, the temperature in the room wasn’t as warm as it was on the last lesson the day before. All the runs that we did were going really slow and so that would have knocked our results into the wrong pattern. That is also one of the reasons not all points are on the line of best fit.
I think my method was good overall, and the temperature was the only thing that spoiled it and I don’t think we were very focused so maybe that was why the timing was out occasionally.
I think our evidence is reliable because if some one did repeat the experiment they would get similar results which probably might be out by most of 2 seconds, so they still would be pretty close.
Our investigation could be extended to support our conclusion by investigating a different factor change. The factor which I will choose to change this time is the temperature. I will be increasing the temperature each time by 5°, and this is will be marked by a thermometer. The rate of reaction depends on the total number of fruitful collisions. Having chosen the factor I am going to predict that as the temperature increases the molecules have more energy to move around faster, they therefore have more collisions. Since the molecules have more energy more of the collisions that take place will actually produce a reaction and form products i.e. more collisions are “fruitful”. It is not necessary to double the temperature in order to double the rate of reaction. I am going to predict that the total number of molecules with velocities greater than that needed for a “fruitful” collision is much larger at the higher temperature. At low temperatures, particles of reacting substances do not have much energy. T higher temperatures, the particles move faster and therefore collide more often. The collisions have more energy, so more of them are “fruitful”. So, the rate of reaction increases.
To make sure my experiment is a fair test I will keep the volume of solution constant. The colour change and density of what is being obscured will stay the same, too. the place where I am going to view the disappearance of the cross will be kept the same. This time I will stir the solution a bit and with constant strength. I will also keep the concentration of solution the same. The only thing that I will be changing this time is the temperature.
In this experiment I am going to observe the colour change when all the reactants have been added together and note down the rate of reaction. I will make only 5 measurements this time, because 6 didn’t really make much difference. First I will get all solutions ready and set up the apparatus. This time I will need a Bunsen burner as well as tripod and safety mat. I will measure the starting temperature and then add on 5° with each run. The first run I will do without heating up the mixture because it will be at room temperature, but then I will heat it up and will have thermometer in the conical flask so that I will be able to tell when it reached the next set temperature. I will have the cross on the side of the flask away from the fire, so that it doesn’t go up in flames ( safety precaution). Last time the cross was underneath the flask but it can’t be this time. I am going to wait for the mixture to go opaque. I will start the stop – clock as soon as I put the last drops of everything in and the temperature is at what it should be.
When I have obtained all of my results I will then plot them on the graph. This is now the plan of the experiment which would provide additional relevant evidence towards my conclusion.
Diana Rough
11L1