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There are four main factors which affect the rates of reaction these are listed below with a brief explanation of how and why this is possible
There are many different factors which affect the rates of reaction and this is one of them the reason why temperature plays a part is because by increasing the temperature you are increasing the rates of reaction. The reason why temperature affects rate of reaction is because when you heat up the solution the particles within the solution move faster than usual this means there will be more collision taking place per second. In addition the particles become more energetic this means that there will be more collisions that take place (the more chances the activation energy needed for the reaction to begin will be achieved).RoR - Temperature
The colder reaction is taking place on the left side as you can see there are not as many successful number of collisions that are taking place. On the right hand side we can tell that the temperature has been increased as you can see the number of successful collisions has more than tripled therefore the rate of reaction is now increased.
If the solution is more concentrated it means there is more particles against less, let's take some water and solvent if you add more solvent to the mix than water the concentration is changed. therefore there is more solvent collisions taking place with the water or vice versa. In addition to the above there is a more chance of a collision with the reactant. RoR - Temperature
On the left we have a lower concentration (less collisions) on the right we have higher concentration (more collisions)
A catalyst is a substance that speeds up chemical reactions without being used up itself. A catalyst works by giving the reacting particles a surface to stick to, which causes the particles to bump against each other; this is then increasing the amount of successful collisions. A catalyst also makes the activation energy for the reaction to take place lower.
Surface area is one of the most important factors because having any solid being broken down into smaller particles compared to larger particles can make all the difference. As a matter of fact smaller pieces (large surface are) will mean that the reaction has more space to take its course so this means that there will be a faster reaction when the solid is broken down.
In this diagram we have marble chips being broken down by hydrochloric acid in this case the reaction is much faster because of the fact the marble chips are much more smaller.
How can these factors be measured?
.using a thermometer
.the amount of gas produced through the syringe
.colour change of chemical with stop watch
.colour change and stop watch
. Time taken for larger piece compared to smaller pieces
. Colour change and stop watch
What is my choice and why?
For my investigation I am choosing the effects of concentration on rates of reaction because I believe that this is the best and most accurate one to use out of all of the above. The reason that I believe I will benefit from choosing the effects of concentration is because of many reasons one of the reasons is because we have all the equipment needed to perform the investigation. The results will be more reliable because you won't have error of equipment because the investigation can be easily completed with just a test tube and the chemicals needed to undergo the reaction.
To carry out my investigation I will need to use the two main chemicals needed for this reaction to take place which is 2 molar hydrochloric acid (HCL) and 0.4 molar sodium thiosulphate (Na2S2O3). The theory is that when HCL and Na2S2O3 react it forms the gas sulphur dioxide as one of its products. Sulphur creates a sharp cloudy colour during the reaction my plan is to harness the fact that once the solution turns into a cloudy colour white the reaction has taken place and finished I can stop a clock watch recording the time it took for the reaction to take place. I will place an X mark on the back of the test tube in which the reaction is going to take place and as soon as the X mark can no longer be seen I will stop the clock.
The word equation for the reaction is: Sodium Thiosulphate + Hydrochloric Acid ------ïƒ Sodium Chloride + Water + Sulphur Dioxide + Sulphur. The balanced symbol equation for the reaction is: Na2S2O3 (aq) + 2HCl (aq) -----ïƒ 2NaCl (aq) + H2O (l) + SO2 (g) + S(s).
The way in which I am going to carry out the practical is very simple and straight forward. I will start by diluting the sodium thiosulphate with water in order to gain several different concentrations needed starting with 20% sodium thiosulphate going down to 100% sodium thiosulphate in intervals of 20% In order to gain the different concentrations of sodium thiosulphate I am going to have to use this formula as my school cannot provide the different concentration sodium thiosulphate This formula will help me to change the HCL molarity to a different one using water to dilute it: M(concentration) X V(concentration) = M(dilute) X V(dilute). I will repeat each concentration level 3 times in order to achieve a mean and create range bars this will hopefully make sure my practical is reliable. Once I have gained my results I will divide 1 by the mean to achieve the rate of reaction then times that by 10-3 so I can get an overall round figure.
My main variables will consist of an independent variable, Dependant variable and of course the control variable. My independent variable will be the concentration of the sodium thiosulphate because I will be diluting it with water in order to gain different concentrations. My dependant variable will be the time which the reaction takes in order for the X mark on the test tube to no longer be visible. The control variable will consist of three major points the timer which I use the purity of the water that I use and also the concentration of the sodium thiosulphate.
As you can see bellow I have worked out the concentrations for my investigation by using the formulae stated above and have compiled it into a table which I will use in the investigation.
Volumes of HCl (cm3)
Concentrations of Na2S2O3
Volumes of Na2S2O3 (cm3)
Volumes of H2O (cm3)
All volumes (cm3)
As you can see from the table above I have made sure that all of the total volumes are of course the same this is done in order to help make the results more beneficial and reliable.
For the last piece of my method I have decided that I will repeat the investigation for each of the different concentrations. I will be doing this all together 3 times for each one in order to achieve a set of results which I can later really on to create a graph with the mean time taken and also with range bars. This will all hopefully increase the reliability of the results.http://t1.gstatic.com/images?q=tbn:ANd9GcQEgkcwnCCTHwvWzZsMGBF7ZqBxrgdDlsG5hZCQ-2j7KRm8Z7Eq5ghttp://luxor.in/UploadImages/ProductImages/Luxor-967_Blue_-Board-Marker-Pen_9000001118.jpghttp://t3.gstatic.com/images?q=tbn:ANd9GcRbJ2SG2_NNhJ5ERIiMs6gyjOPZr4DCDV9a6ZmyB2VEEcu2qWCHhttp://www.labandscience.com/images/T/Test%20Tubes.jpghttp://www.google.co.uk/images?q=tbn:XEpGqEy6lGDDOM::www.labtitan.co.uk/images/Measuring%252520Cylinder%252520100ml.JPG&t=1&h=94&w=70&usg=__iImwpIrTrAFJfSLr9cfNg0Ukybo=
Measuring cylinders X2
Test tubes X5
0.4 molar sodium thiosulphate
2.0 molar hydrochloric acid
Safety goggles X1
Board marker pen X1
Stop watch X1
Volumes of HCl (cm3)
Concentrations of HCl
Concentrations of Na2S2O3 (moles)
Volumes of Na2S2O3 (cm3)
Volumes of H2O (cm3)
All volumes (cm3)
As you can see from the preliminary results the table I have used is not very suitable for the results I have collected. Therefore, I have made my final adjustments to the table and created one that has all the correct volumes and concentration mixes.
In addition to my preliminary results I have decided to add a burette for my final investigation. The reason that I have chosen to add the burette is because I found that when measuring the Hydrochloric acid, water, sodium thiosulphate even the slightest jolt can cause havoc on the results table. By adding the burette I believe I can make my results more reliable this is because by using the burette we can measure the chemicals more easily and also more efficiently.
Final results table
Volume of Na2S2O3 (cm3)
Volume of HCL (cm3)
Volume of Water (cm3)
Concentration of Na2S2O3 (%)
Total Volume (cm3)
Test 1 (S)
Test 2 (S)
Test 3 (S)
Average Time (S)
Rate Of Reaction (X 10Ë‰Â³)
Analysis of final results
As you can see from the results that I have gathered there is a clear correlation between concentration Sodium thiosulphate and rate of reaction. As the concentration of sodium thiosulphate increases the time taken for the solution to go cloudy is faster.
As evidence for the above we can see from the results that the reaction took place fastest when there was 100% concentration of sodium thiosulphate with no water. The results that I have achieved above match the theory of the effect concentration on the rate of reaction. The theory clearly states that the more particles there are against another the number of successful collisions increases. My results show exactly this because when there was only 20% of sodium thiosulphate the rate reaction was 4.541 whereas when there was 100% concentration of sodium thiosulphate the rate of reaction was 33.910 this clearly faster than the rate of reaction for 20% concentration of sodium thiosulphate therefore approving the theory of the effects of concentration on the rates of reaction.
I believe that my results were very reliable this is due to many reason. One reason would be the fact that the graphs that I had elaborated from the results that I had collected managed to form a very dependable line of best fit. Another reason would that when I had looked at the results collected from other students within the class I started to discover that the correlation between the factors all where rising and a similar trend emerged. One thing that made my results different to the rest was because my results showed a superior difference compared to the others results and graphs. This made me even more self-assured about my results. The last bit assurance came from the range bars which I had created in graph one all the ranges of the results for each concentration where very close to one and other this instantly tells me that my results are more reliable.
Technique and equipment precision
The technique I used in order to complete my practical was very straight forward and simple I used the following layout shown below. I used many different apparatus one of the main things that I knew would increase my reliability was the use of the burette. The reason why I believed this is because it helped me to measure out the chemicals including sodium thiosulphate and also the hydrochloric acid with more accuracy. In theory I believe that the technique we used was very reliable this was because we used all the more reliable apparatuses. This was done in order to complete my practical very reliably instead of just pouring the chemicals I used the burette. This also helped me gain that extra precision needed for the practical.
Overall I believe that the investigation that I carried out was a success. There are many reasons for which I believe that the practical and the results success and trustworthy. One of the main reasons was because the results I had collected from the three trials seemed very close to one and other (ranges). This indicates to me that my results were very dependable because there were no outliers, we can see this from the graph that I had made from the results. In addition the line of best fit seems to display a positive correlation and this helps to prove the theory that was stated about the effects of concentrations on the rates of reaction.
The ranges that I used I believe are very respectable this is because of the differences in results, they all were separated from at least a 10 second margin. One reason why in the future I would like to keep a larger range would be the fact that the results would be much more clearer and the trend of the graph would represent this due to the fact I wouldn't have had to change the recording to the (10'-3).
In conclusion I believe that I have collected enough a more than sufficient amount of data to compile my results. This is because I have collected three repeats of every different concentration which totals up to twelve repeats in total. Therefore I believe that the amount of data that I have collected is more than the sufficient amount to analyse and record the rates of reaction and also answer the question I began with.
If I could do the investigation again
If I could do the investigation there would be a number of factors that I would change or evaluate. One of my main concerns would have had to be the problem with everyone's visual aids. As we all know different people have different eye sight and throughout the investigation this turned out to be a cause for concern. The way in which I would change this would be to use a digital video camera a computer/laptop and a computer software that would monitor the colour change within the solution until the point the cross was no longer visually present with us. This would in defiantly increase the chances of reliability after all a computer is much more reliable than our eye sight the setup for this addition is shown below (similar setup to data logger). One other major modification would be to do the investigation within a fume cupboard at first this may seem very ludicrous but I can surly change your mind about this. The reason why I would have used a fume cupboard would be because the whole class was carrying out the investigation in the class room there must have been many abundant gasses such as sulphur dioxide. By carrying out the investigation within a fume cupboard my investigation would not be harmed from these abundant gases thus making my investigation even more reliable. The reason why all of the above would advance my older method would be because by adding the computer enhancement and fume cup board I would be able to obtain more trustworthy readings.
As you can see from the diagram the computer and camera will stay outside of the fume cupboard because of various different safety reasons. The camera will be recording the reaction which is taking place within the fume cupboard the information will be transferred from camera to computer via a composite usb cable. The computer will be loaded with a professional colour detection program which will stop the camera once the reaction has taken place and that will be the time that we will be recording for the rates of reaction.