I predict that the greater the concentration of thiosulphate solution the faster the reaction, and so the faster the solution will go cloudy. I will use different concentrations so that I will get a good range of results.
If when I have got my results it turns out to be true that the times taken by the reactions do decrease I shall actually plot "1 over Time taken", i.e. the "reciprocal" of the time taken. This is because plotting the reciprocal will produce a graph showing a positive correlation.
Apparatus: -
I decided to use these concentrations during my preliminary series of experiments –
2 mol. of HCl (acid concentration will be fixed)
0.4, 0.8, 1.2, 1.6, 2 mol. of sodium thiosulphate (this is my variable)
Using my preliminary experiments I decided on using the following apparatus:
1 beaker
2 measuring cylinders
1 conical flask
1 stopwatch
1 piece of paper with an X marked on it
1 pair of tongs
1 pair of goggles
Method: -
Changing the concentration
20ml of HCl and 20ml of sodium thiosulphate solution are poured out into two measuring cylinders and then poured into a conical flask, which is placed on top of a piece of paper marked with letter X. Once they are both in the conical flak I then stated the stopwatch. When the mixture has turned cloudy so that the letter X could no longer be seen the stopwatch was stopped and the time was recorded. The experiment is repeated with all the concentrations. The whole procedure is then repeated four times to ensure that I have a fair test and then I can calculate the averages then the rate of reaction.
Safety: -
A pair of goggles was worn during the experiment in order to protect the eyes from any possible splash that might be caused by the sulphur dioxide released. When handling beakers and measuring cylinders I used a pair of tongs. Care was taken to protect the table from acid I also tucked in any of my loss clothing to prevent it dipping in the acid.
Fair Test: -
In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the HCl and thiosulphate will not be mixed up. The amount of HCl will be 20ml each time, and the amount of the thiosulphate solution will be fixed at 20ml also.
Prediction: -
I predict that as the concentration of the sodium thiosulphate increases the rate of reaction will increase. This means that the graph drawn up in my analysis will have positive correlation.
Results.
Shown below are my four results tables and the fifth table is a table that shows the averages and the rate of reaction. Rate of reaction was calculated by doing.
1
TIME
Shown below is my graph of results. The computer generated one is showing concentration of hydrochloric acid and the average time(s). the second hand drawn graph shows the concentration and the rate of reaction.
Conclusion
As you can see from my graph for time V concentration that the graph shows a weak positive correlation and the line is rather straighter that I expected. I expected the line of the graph to be a lot more curved. Adding also that when you look at the graph for the rates of reaction you can quite easily see that it shows a strong negative correlation. The line of this graph goes in a straight line like I expected it to.
In my prediction I predicted that, as the concentration of the hydrochloric acid increases the rate of reaction will also increase. So as the concentration gets weaker the time taken for the solution to go cloudy will be of a longer period of time. I think now that I have completed the experiment I can quite easily state that the prediction that I made was very good and accurate.
I think that if we done this investigation in the summer we might have had different results because in the summer the temperature in the room is a lot hotter than in the winter and that might have had an effect on the overall readings. Also if we had a stronger solution perhaps the results might have been effected.;
