When I am heating up my chemicals I’m taking into account that all the particles will have to be heated up (otherwise it wouldn’t actually be the temperature) so something at the specified temperature will have to surround the entire substance. The most suitable substance is water. If I use a water bath then I can easily heat up my substance.
The last thing to say is that distilled water will be used because it will not affect the sodium thiosulphate in any way except dilute and lower its concentration.
Now that I have thought these 2 things over I can now continue with making my procedure.
Apparatus-
The following items will be all that I need to do my experiment. The procedure will tell me how to use these items.
- Conical flask
- 2 measuring cylinders
- A sheet of paper with a cross on it
- Water bath (for different temperatures)
- Hydrochloric acid
- Distilled water
- Sodium thiosulphate
- Thermometer
- Stopwatch
Procedure-
The first thing to do is know what temperature you are going to do the chemicals at. So, just for an example, we choose the temperature to be 30oC. We then get a water bath that’s at that temperature (the water bath is just an apparatus that contains water and has a mechanism to heat it up to specific temperatures). Then we use 1 measuring cylinder to measure out the correct amount of hydrochloric acid and the other to measure out the sodium thiosulphate and distilled water. We then put the diluted sodium thiosulphate into the conical flask. Then we put the measuring cylinder with acid in it and the conical flask into the water bath with the chosen temperature (the water level of the water bath should be high enough to overlap the level of hydrochloric acid or sodium thiosulphate within their containers- this should heat up the 2 chemicals equally). Then we put the thermometer in the sodium thiosulphate and wait until it the thermometer reads the same the temperature as the water bath’s temperature (this may take 3 to 5 minutes depending on what temperature you are doing). When the thermometer has the correct reading you must take out the conical flask and put it on a cross, which is drawn on a sheet of paper and then put in the hydrochloric acid. As soon as the acid hits the sodium thiosulphate start to time how long it takes for the cross to disappear as the 2 chemicals react and go cloudy. This must be done as quickly as possible as you want as little heat to be lost as possible. Once the time has been recorded you then wash out the conical flask with water.
You then repeat the test with either a different temperature water bath or the same, remembering to use the same measuring cylinders for the same chemicals or just getting new ones. Once I have all my results I will create averages from the repeats and then make graphs to analyse.
When I take a room temperature reading I will do the exact same method as above but I just won’t use a water bath. I will not anything below that temperature as I feel that I will have enough results afterwards.
Diagram-
Fair Test-
To keep this experiment fair (which means keeping my results as accurate as possible) I have to keep everything as constant and accurate as possible. This means that all my equipment will have to be used the same way and as accurately as possible in each test. It also means that the sodium thiosulphate or hydrochloric acid measurements can’t change (including the concentration of the sodium thiosulphate). Although the temperature will vary it will still have to stick to one value in one test. All these values; the concentration and measurements, that are mentioned here will be found out within the preliminary test.
The main factors that I have to keep fair are the temperature and the measurements. This means that the temperature has to stay as constant as possible and the measurements as accurate. To do this I will make sure that the temperature is definitely correct before I take out the flask and measuring cylinder and then when I take out the two apparatus I will be as quick as possible in placing the flask over the cross and pouring in the acid. I will also make sure that when I place the flask and cylinder in that their substance level is completely submersed, so that all the particles become the right temperature. When you start timing it would be better to have a friend so that one person could say when to start timing and then to also tell him when the cross has disappeared. If you did it on your own you would be concentrating on more than one thing and you may start or finish the time wrong. The only thing that I can say about the measurements is that I will measure it to the exact value for every test. I will also use smaller measuring cylinders if I am measuring smaller quantities, this way I will get more accurate readings. In this way I will also get the right concentration as well.
I will also never mix up the measuring cylinders as any remains of a chemical from a previous experiment may mix and cause an early reaction, ruining that test. It also applies to the thermometer; I will never take temperature readings from both chemicals, I will always stick to one chemical to take the temperature of. When washing out the flask I will make sure it is all washed out, as any previous chemicals will ruin the next test.
When timing the room temperature test I will leave the flask for a couple of minutes before starting the test as there may be a temperature left from the water that I washed the flask out with. Once the flask has reached room temperature I will continue with the test.
I will mention here that for the two substance particles to collide they need to be sufficiently mixed but if I wait for them to mix then the temperature will have gone and I also wouldn’t be able to tell when they have mixed well enough for me to time. I will therefore just start timing as soon as the acid first hits the sodium thiosulphate. I know that this will distort the results as the temperature varies the time it takes for the chemicals to mix but if I make all the repeats constant in timing then I will get an accurate average.
Safety-
Since I’m handling corrosive substances I will obviously take care, gloves will be used, as will goggles, the chemicals will be safely poured away and extra care will be taken when pouring the acid and sodium thiosulphate into the measuring cylinder.
Prediction-
I predict that as the temperature rises so does the reaction rate. This is because as you heat both the hydrochloric acid and sodium thiosulphate their particles speed up, giving them kinetic energy. This extra kinetic energy makes them move faster, which means that they’ll hit something quicker and also it also gives them more energy to break the bond of the other particles. I also predict that because the temperature affects two factors to make the reaction faster that there will be an upward curve on the graph. This is because the two factors (speed and energy) both make the reaction faster and so instead of just a steady straight line that shows a constant increase they will make it faster and faster, which means an upwards curve. Unfortunately though conventional graphs have time which start at 0 but since the higher the time in this experiment the slower the reaction rate the time axis will have to start with 0 at the top to follow this curve rule.
Predicted graph:
0
So when looking at my graphs keep in mind that although, on first sight, it looks like that the rate of reaction is decreasing it’s actually increasing.
Preliminary Test-
When doing my preliminary test I plan to find out what concentration of sodium thiosulphate I will use and what range of temperatures I will use. The concentration of sodium thiosulphate will include me finding out what two measurements of the distilled water and sodium thiosulphate make up the best intermediate concentration of 25cm3 (e.g. 5cm3 + 20cm3). To do this I will use the same method as above but in room temperature, so no water bath and do every combination of sodium thiosulphate values plus distilled water values to make up 25cm3 and see what time is the most logical to use (not too long and not too slow).
To find out my range of temperatures I will do the same method as above on room temperature and on 50oC. These two results will tell me if there will be varied enough results between these two results to make a good graph/analysis. If there is a large gap between these 2 results then I can guess that there will be sufficient results, if its too big then I know that I will have to decrease my temperature from 50oC, if its too small then I know that I have to increase my temperature from 50oC. These increases or decreases I will just have guess from the gap in between my 2 original results.
Preliminary test to find the concentration of the sodium thiosulphate
From this table of results I can see that at room temperature the 1st two results are too fast (any other results at a higher temperature would be impossible to read), and the last are over 100 seconds and so are too slow. Therefore the only one left is 74 seconds, this is intermediate and so is perfect for my experiment. My sodium thiosulphate concentration will therefore be 15 cm3 sodium thiosulphate and 10 cm3 distilled water.
Preliminary test to find the temperature range-
So from this table I can see that there is a difference of 61 seconds between 20 oC and 50 oC. If I go up in 10 oC for every test then I should get a good enough range between my results of time. That would give me 4 results of averages on my graph. I feel that is not enough so I will go up to 60 oC and have 5 results instead. 5 results should give me a recognisable pattern.
Experiment-
I will apply all that I’ve said into these results.
Results:
I will now use my average set of results to make a graph. Then I will analyse the graph and see whether or not my prediction was right.
Graph:
Please Turn Over
Nic do not delete this, it’s the page wher the graph goes, but u have 2 include it otherwise the page no.s would muc up.
Analysis of graph:
When looking at this graph keep in mind what I said earlier; the lower the time the higher reaction rate.
This graph proves my prediction to be correct. The graph did curve as I expected and so it does prove that as the temperature rises, so does the reaction rate.
Experiment Conclusion-
First of all let us remind ourselves of my experiment aim; ‘how temperature affects the reaction rate of the reaction between sodium thiosulphate diluted with distilled water (these two substances make up 25cm3) and 5cm3 of hydrochloric acid’. From looking at my results I can now say that temperature affects the reaction between sodium thiosulphate and hydrochloric acid by raising its reaction rate with a rising temperature. So as the temperature raises so does the reaction rate.
The reason behind this is because heat vibrates particles and so produces more kinetic energy in the particles. This does two things, increases the speed of the molecule and gives it more energy to break the bonds of other particles easier. This, in turn, increases the reaction rate because the extra speed means more collisions (which leads into more likely reactions with the extra energy) and the extra energy makes reactions more frequent. So the heat, we can see, increases the reaction rate.
Within this explanation I’ve explained my prediction that ‘as temperature increases so does the reaction rate’ and my graph proves true my predicted graph.
Evaluation-
Analysis of results-
I am pleased with my results as they answered my aim well and proved my prediction. I didn’t get any anomalous results and my line of best fit nearly followed the points perfectly.
Reliability of results-
I think my results could be a lot more reliable. This is because there are a lot of things that can go wrong with my current method. The main thing is that the heat can be lost when doing the experiment. As you take out the flask and measuring cylinder it immediately starts to lose heat and as you go on through the test it loses heat continuously. So that is something that distorts the results. It is particularly so for high temperature tests as they would have lost heat quicker in the comparatively cold room temperature.
Changes to make?-
If I were to do this test again I would change the method so that instead of having to take out the flask I would leave it in there and have a cross within the water bath of which to place the conical flask over. Maybe the cross could just be a laminated piece of paper with a cross drawn on it, in that way the paper wouldn’t be affected.
Is my conclusion firmly proved by my results?-
Considering the flaws of my method, which is mentioned above, I think that probably my conclusion isn’t very firm. But then I look at how well my results fit in with my line of best fit and see that the conclusion must be firm. It doesn’t particularly matter, as my results were firm enough to produce a conclusion that proved my prediction to be right.
Further work?-
If I were to do further work I would either try out my new changes that were mentioned above and perhaps increase the range of my temperature to make my pattern even more clearer and more accurate. This would prove my conclusion further.
Otherwise I would try out some more factors involved within this experiment. Instead of changing the temperature I could change other factors like the concentration of the sodium thiosulphate or the amount of acid added.
Overall though I think that this was a very successful experiment and that I have managed to gain and analyse some useful results that told, explained and answered me a lot. I have also set myself some more questions for me to answer in any other extra experiments that I may do in the future.
