Equipment List
100cm3 Conical Flask
Tripod
Bunsen Burner
Gauze
Stopwatch
Hydrochloric Acid
Sodium Thiosulphate
Water
50cm3 Measuring Cylinder
10cm3 Measuring Cylinder
Tongs
Thermometer
Heat proof mat
0-110 oC Thermometer
Diagram
Method
In my experiment I will first collect my apparatus: measuring cylinders, tripod, etc (refer to equipment list) and set it up as in the diagram on the previous page. I will then continue to measure out 30cm3 of Sodium Thiosulphate, 20cm3 of water, and 10cm3 of Hydrochloric Acid as I have stated in my preliminary work earlier. This will make the total volume of liquids up to 60cm3.
I will then pour the Sodium Thiosulphate and water into a 100cm3 conical flask. Aftr this I shall put the conical flask onto the gauze and tripod and heat it using a bunsen burner until I get it as close to the desired temperature as possible. I then take the temperature of the Sodium Thiosulphate and water with a 0 - 1000C thermometer and put the conical flask on top of a black cross on white paper. We do this quickly so that we lose as little temperature as possible. Next I am going to add the Hydrochloric Acid and immediately start the stopwatch. When I am waiting for the reaction to take place I am going to be looking through the top of the conical flask each time to make sure that the experiment is fair. Once the reaction has taken place I stop the stopwatch and record the final temperature along with the reaction time in my results table.
After the experiment is done I will rinse my apparatus thoroughly to remove any excess particles and keep the experiment fair as I will go on to explain. I will repeat this same experiment three times for each of the following temperatures: 200, 300, 400, 500, and 600. I will do this so that I can obtain an average reaction time for each temperature. These temperatures will be within 20C of the designated temperatures because due to human error, I cannot gain a temperature of exactly 200C, 400C, etc.
Fair Testing
To make sure that my experiment is fair I will make sure that I completely rinse all of my apparatus. I will do this to remove any particles fromprevious experiments so that there are the right amount of paritcles and therefore the right concentration. I will also make sure that I use the same volumes of each liquid (30cm3 of Sodium Thiosulphate, 20cm3 of water and 10cm3 of Hydrochloric Acid) to keep the concentration the same and keep the number of particles the same. I will not stir the chemicals at all and I will try to move them around as little as possible. This is to prevent any unwanted collisions which may inadvertantly speed up the rate of reaction. I will record the temperature of the liquids at the start and end of each experiment to find an average temperature for that particular experiment and so I can see any faults in the temperature of the liquids. One of the main aspects of my fair testing will be that I repeat my experiment for each temperature three times. I will do this so that I can obtain an average and also so that I can repeat any experiments further if they do not seem to fit in with the rest of my results. For example, if for one particular temperature, my times were 60 seconds, 62 seconds and 80 seconds, I would repeat the odd experiment to try and get another result which was more appropriately fitting to the rest of the experiments.
Safety
In my experiment I will try carry out everything as safely as possible. This will include:
Not running - There will be people walking around with chemicals and hot liquids and glassware. You could fall and hurt yourself and/or others. You could run into or knock someone carrying hot materials or chemicals and as a result they could end up spilling them on you or themselves.
Wipe up spills - If you spill something it must be cleaned up quickly and appropriately. Someone could slip on chemicals which had been spilled on the floor and hurt themselves.
Wear goggles - You must wear goggles at all times when heating chemicals in case they spit or splash out of the test tubes. They may get into your eyes and blind you.
Acids are corrosive - This is basically the same as wiping up spills but this also involves carrying and handling the chemicals. Be careful not to get it onto your skin.
Report breakages - You must tell the teacher if you break any apparatus including glassware. Someone may not notice it and cut themselves on it.
Use tongs when carrying hot glassware - Tongs must be used or else you burn yourself and/or drop some apparatus containing chemicals.
Analysis
I predicted that if I doubled the temperature, then the rate of reaction would more than double because not only would the particles be moving faster to create more collisions, but they would also have more energy so there would be more successful collisions. My results and graph have proved this to be right. If the rate of reaction reaction has more than doubled, then the time taken would have more than halved as the temperature doubled. My graph shows this:
20oC = 68 seconds
40oC = 26 seconds
60oC = 11 seconds
I think that the result which my graph shows for 20oC (68 secs) could be wrong because my results table shows my average temperature as being 75oC and thi is too far out to be accurate.
Evaluation
I think that my experiment went pretty well overall. If I could do anything again with more time I would have spent more time getting my starting temperature closer to the designated temperature. My temperatures were close enough together as they were all within 5 seconds of each other. I only had 1 anomolous result and I only had to repeat it once as I got a result which fits in with my other results for that particular temperature. My experiment would have been fairer and more accurate if I had used the following equipment but these factors were beyond my control:
The thermometers we use in school are alcohol thermometers and are not 100 % accurate. Mercury thermometers should have been used as they are far more accurate but they are not allowed in school. Also a waterbath could have been used to programme the liquids to the desired temperature. This is much more accurate than a thermometer reading.
The plastic measuring cylinders we used to measure out our liquids are mass produced and so are not 100 % accurate. A glass pipette should have been used as they are hand made and much more accurate. Also glass is clearer than plastic so you can take a reading of the liquids easier and more accurately.
The substances we used were made from stock solutions which were made fresh every lesson therefore the concentration of these substances changed slightly from day to day during the experiment.
The equipment was rinsed with tap water which contains many impurities which may have contaminated or changed theconcentration of the liquids. Distilled water should have been used as it is pure and has no impurities but once again I didn't have the time to keep distilling more and more water just to rinse my equipment.
