Dealing with temperatures is a difficult task, especially when we have to keep constant high temperatures. Secondly the rate equation and the constant k changes when the temperature of the reaction changes. We have no gases and solids involved therefore it is easy to deal with solutions. Similarly the use of a catalyst complicates things, and if used incorrectly could alter the outcome of the experiment. The theory behind this experiment is that 'Increasing the concentration can increase the rate of the reaction by increasing the rate of molecular collisions.' This means that since there are more reactive atoms in the solution, so therefore there are more collisions with other atoms.
Preliminary Plan
When deciding what we should do for our preliminary experiment, we discussed the necessity of determining the range of results that we could expect when properly conducting our experiment. We came to the conclusion that we should establish the highest possible rate, a median rate and the lowest possible rate, therefore achieving a rough outline of what to expect in the experiment.
Preliminary Results
These results show the approximate range of results that we could expect to find in our further experiment. There were no outliers, so there was no immediate need to repeat the results more than twice.
From this, we can find out the rate of these reactions by using this formula:
1,000
Time
Therefore, the rate of reaction added onto this table would look like this:
These results compared with those from our main experiment can show us how accurate we have been in conducting it.
Safety
There are a lot of safety issues we must abide by in this experiment. We must remember that the substances which we use in this experiment can be very harmful if used the wrong way.
When we do this experiment, it may be necessary to wear safety goggles, as things are very unpredictable, and even though it is very unlikely that the solution would come out of the beaker during the experiment, one must still be cautious of spills.
We must make sure that coats and bags are all out of the way while doing the experiment. Ties and hair should be tucked out of the way, so they do not make contact with any of the chemicals. It would also be preferable to wear a scientific apron, however this is not essential.
We should also try our best not to spill any chemicals, and we must not eat or drink in the lab while dealing with these harmful chemicals, as they can get on to our hands.
Fair Test
To make this experiment a fair test, we need to make sure we do a number of things. In this experiment we are trying to find the rate of reaction using concentration as a factor, so there is a number of things we need to make sure we do to keep it a fair test.
Firstly, we need to keep a chemical at a constant concentration. So, in this experiment we have chosen to keep hydrochloric acid at a constant concentration (5cm3). We could have, however, used Sodium Thiosulphate as a constant, but we had chosen to use Hydrochloric acid.
Next we must make sure that the solution is kept at a constant volume throughout the experiment. If the volume is different, then it could give different results to if it was at a constant volume. We must also make sure that we add both the water and the Sodium Thiosulphate at exactly the same time (into the beaker with the hydrochloric acid in it), or it could affect the results of the experiment.
We must start the stopwatch at the exact time as we put the water and the Sodium Thiosulphate into the beaker. To do this it is a lot easier if there are two people doing the experiment, so one person can put the two substances in the HCL, and one person can start the stopwatch. Also the person timing the experiment will look for the disappearance of the cross, otherwise there would be a time lapse between seeing the cross disappear and telling the other person to stop the clock and then eventually stopping the clock.
It is also important to keep the temperature the same to obtain fair results, however we do not have to worry about this as the temperature will be kept at room temperature through out the experiment. It could be said that as our experiments will be carried out on different days, the temperature would differ dramatically. This is true, but there will only be minute temperature differences, and we would not be able to control the room temperature at which we carry out the experiments.
It also important we keep the colour and size of the cross the same this will help keep the results fair for the experiment. Another thing we must do is to make sure that the beaker is completely clean and free of any water or any other substance before we attempt to start the next experiment.
Method
Firstly, we measured 5cm3 of hydrochloric acid from a burette, to ensure that we had the upmost accuracy in our results. We placed the acid in a beaker, and then put the beaker on a black cross on a piece of laminated paper. We then added 50cm3 of Sodium Thiosulphate, also measured using a burette, to the hydrochloric acid, and at this time we do not need to add any water. Immediately, we started the stopwatch. We then waited for the black cross to disappear. When it had become too cloudy to distinguish its whereabouts, we stopped the stopwatch. Then we recorded what the time was.
We then emptied out the contents of the beaker, cleaned it out and dried it out to ensure that none of the reactants were still present. Next, we added 40cm3 of Sodium Thiosulphate; we kept the HCL acid constantly at 5cm3. Because we have to keep the volume the same for it to be a fair test, we added 5cm3 of water (we had to add the Sodium Thiosulphate and the water at the same time for this to be a fair test). We then recorded the time for the cross to become completely obscured.
We repeated this many times, adding different amounts of Sodium Thiosulphate and water each time, and recording the time taken each time. To ensure that our results were relatively accurate, the same person took the measurements each time.
Evaluation
Since we took enough results to draw a conclusion, I think that ours was fairly accurate. We used a burette for measuring