Method
Equipment
The equipment that I will need for this practical part of the investigation is;
- Pipette
- Burette
- Conical flask – 250ml
- Stopwatch
- Goggles
- Measuring cylinders
- Clamp stand
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Sodium Thiosulphate – 25cm3
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Hydrochloric acid – 50cm3
- Thermometer
- Cross board
- Kettle
- Pen
- Paper
Safety Issues
I will have to consider safety issues whilst carrying out my investigation for obvious reasons. Goggles will have to be worn to prevent any substances that are being used going into my eyes. Safety in the actual lab has to be considered, all stools have to be pushed under the desk out of the way and coats and bags have to be out of the way in the corner of the classroom where the coat pegs are. Also I have to be alert to respond to any instructions that the teacher has to put forward. The practical work has to be taken seriously and ‘playing about’ cannot be an option, as this could endanger other people as well as me.
Fair Test
I will have to keep this investigation a fair test so that my results are accurate as much as they can be. The way that I will keep it a fair test is that I will only have one variable and I will accurately measure my substances. I will also when investigating at different temperatures only proceed with my practical work when the temperature is at its most accurate. Also the same person has to be judging when the cross disappears as people have different eye sight levels. Some may be very short sighted and another very sharp and this difference can alter the supposed rate of reaction.
How will Temperature be changed?
The temperature of HCl and Na2S2O3 will not be altered by heating the substances in a test tube over a Bunsen burner because, you are heating the substances directly above the flame although you may turn off the Bunsen when it says 50°C the conduction of heat energy still carries on and the true actual temperature of it could really be 60°C. The most accurate way to get the temperatures equalling what you want is to heat water and put the reactants into a test tube then put the test tube in the beaker containing water and monitor the temperature from there. This is a more reliable way, as the conduction that takes place after you have heated them, is less than if you had have heated them directly which means it is more likely to be closer to its true temperature.
I plan to record my findings in a table like the one below;
The reason that I plan to repeat my experiment is because by having two sets of results I wish to find an average to increase the reliability of the results.
Average = Results ÷ Total number of entries
When I have worked out an average I will put my workings in a table like the one below and calculate rate;
Independent variable: Temperature
Dependant variable: Rate of reaction
Step by Step Method
- Gather equipment needed and put on safety goggles.
- Get the cross board and put a beaker on top of it
- Get ready with the stopwatch
-
Fill burette with 50cm3 of Na2S2O3
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Pour 25cm3 of HCl into pipette and release that into a test tube
- Put water into kettle
- Turn on kettle and heat the water
- Pour the heated water into two beakers
- Put the test tube that you have filled with HCl into the water
-
Pour the 50cm3 of Na2S2O3 into a test tube
- Put this into the water filled beaker also
- Insert a thermometer into both of the test tubes
- Wait for temperature to reach desired rate
- Obtain the test tubes
- Pour both substances into the beaker which is on the top of the cross board
- Start the stopwatch
- Observe – wait till cross is not visible
- Stop the stopwatch
- Record results
- Reset the stopwatch
- Wash out all containers that had substances in them
- Repeat step 4 and onwards all over again but make sure you monitor at different temperatures.
Results
Working out Averages;
15°C = 34:53 + 51:03
= 85:56 ÷ 2 = 42:78
30°C = 28:06 + 31:10
= 59:16 ÷ 2 = 29:58
45°C = 11:63 + 13:42 = 25:05
= 25:05 ÷ 2 = 12:525 which rounded to is 12:53
60°C = 04:35 + 05:25
= 09:60 ÷ 2 = 04:80
75°C = 02:46 + 03:01
= 05:47 ÷ 2 = 02:735 which rounded to is 02:74
Calculating Rate
To calculate the rate of a reaction I need to divide 1 by the time taken for the reaction to be completed using the averages that I have worked out. I then will plot the graph for my average time against temperature and rate against temperature, and analyse my results.
Rate = 1 ÷ Time
15°C = 1 ÷ 42:78 = 0.023375409
30°C = 1 ÷ 29:58 = 0.033806626
45°C = 1 ÷ 12:53 = 0.079808459
60°C = 1 ÷ 04:80 = 0.208333333
75°C = 1 ÷ 02:74 = 0.364963503
Rounded to 4 decimal places is;
15°C = 0.0234
30°C = 0.0338
45°C = 0.0798
60°C = 0.2083
75°C = 0.3650
Conclusion
By looking at my graph (Temperature VS Rate of Reaction) I can see a trend; there is a negative correlation. As the temperature increases the time taken for the reaction to occur decreases, as the higher numbers are at the top of the graph this causes a ‘left to right trend’. This graph is inversely proportional as when one variable increases the other decreases. I have noticed that by increasing the temperature by 15°C each time the average rate of reaction half’s each time, this is not that accurate but it is the general rule. I was correct in my prediction by saying that by increasing temperature I would decrease the rate of reaction. I knew that when a collision took place (an encounter between two or more particles that come together or close to each other) the exchange or transfer of energy would take place if sufficient Ea is present. If there was not enough Ea then the particles would not react. The collision theory stated that the more collisions that particles undergo the greater chance of reacting particles colliding which results in a more rapid rate of reaction. This would mean that if particles had more kinetic energy which meant that they would move faster, than they would undergo more collisions. So theoretically speaking if the reactants have more kinetic energy they react quicker. This led me to think how kinetic energy is connected to temperature. By increasing temperature you are transferring energy to the particles, this is kinetic energy and the particles move more frequently, therefore by increasing temperature you increase the kinetic energy of particles so there are more particles with more Ea required for a reaction to successfully combine and more successful collisions- thus a quicker reaction as temperature is increased. I predicted a graph of what my results would look like based on the background science that I knew and I produced this graph as part of my prediction;
As you can see the actual graph that I did produce looks similar as the one above. The values are not close to the actual ones that I did get but, the general trend is there.
Evaluation
I have not really found out anything major in this coursework but it has strengthened my understanding of rates in reaction overall and how you can combine different ideas to come to some sort of prediction about whatever it may be. I am interested to see how reliable my results are I will plot the two attempts of the investigation next to each other and analyse them;
Series one indicates the first attempt and series two the second attempt. As you can see the dots are quite far apart especially at the lower temperatures, this means that there is a difference in rate of reaction and if the experiment was done more precisely then the dots would have been closer together and a more accurate experiment. Possible causes could have been because the different set of results was done on different days and a different person judged the cross disappearing and the differences in eye vision would have caused these not so precise results. Also the anomalous results could have been down to the volume of reactants and the actual temperature getting measured wrongly. I think to have increased the reliability even more I should have at least had 5 attempts at each temperature range then have had found an average, as well as getting a second opinion on measuring the volume of HCl and reading the temperature and the time taken e.t.c. Also if I was to do this experiment again I would use a light meter to help indicate when the cross has disappeared as this is a more precise way to carry out the investigation.
