Preliminary Work
The main aim of preliminary work is to find the appropriate apparatus and find the correct materials which will be used throughout the experiment. It is important to collect a certain amount of data, but not too much off data. My main task my to choose an appropriate limestone, because there were various different sizes, also I had to choose an appropriate weight for my limestone.
When I carried out my preliminary work I decide to use different sizes of limestone, and also used different weights.
I will use a concentration of 30cm³ of acid, and also I have decided to collect 30cm³ of gas. The reason behind this is because gives a sufficient amount of time, for the limestone and acid to react, because if I was to collect 15cm3 of gas, the times would be very close together and also not all the limestone would react and therefore I will not no when the reaction happen the most.
From doing my preliminary work I have found various results because, I have used four different limestone’s and also I used 10g or 5g of limestones. From studying my results table I believe that I am going to use 5g of limestone, this is because the reaction happen a bit slower and another main reason is that when I put 10g of limestone into the boiling tube, the acid suddenly overspills out of the boiling tube. On the other hand the size of limestone which I am going to use for my investigation will be the medium chips, because me and my partner decided that the time were appropriate, because they were not too fast or too slow. So for my investigation I will be using the medium size chips and 5g instead of 10g.
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Method
I will set up the apparatus as shown in the diagram. First we filled the trough with tap water about half way up and filled the measuring cylinder with water and then I poured the water into the Gas burette, afterwards I turned the Gas burette upside down into the trough so the cylinder was still filled with water. Then we clamped the Gas Burette in place. We then put the delivery tube under the gas burette so the air from the experiment could displace the water. To make sure the volumes of acid and water were right we now measured the volumes of each in a measuring cylinder to be accurate. To make sure the mass of marble chips were right we measured on the electronic balance too two decimal place. Then we put the chips and the acid in the conical flask and I will be using 1M acid throughout the experiment and started the stopwatch until it collected 30cm³ of gas. I will repeat this process as many times until I have a sufficient amount of data.
Here is a blank results table which I am going to use:
I will be using 5g of limestone for each experiment and also I every time I will collect 30cm³of gas. Another point is that I will be using 1M of nitric acid. I am going to repeat my experiment two times so I get three sets of results, then afterwards I will average them out, then finally find the rate of reaction.
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For this experience I will need a number of apparatus as followed:
Bung, conical flask, Bung, Delivery tube, gas burette, clamp, trough, water, limestone (5g each time), stop watch, Nitric acid, top pan balance, measuring cylinders.
I will also have to have access to tap water.
Accuracy
To keep my investigation as accurate as possible in order to get the best results, here are some of the techniques I am going to use:
- I will start the stopwatch as soon as the first bubble of gas is seen; I will do this every time. This will also keep the results fair, if I started the clock before the first bubble or after the results will not be fair as I have not done the same for all the tests. This will also aid the accuracy; as if I follow the same procedure then the results will be as accurate as possible.
- As I am filling the gas burette with tap water, when it’s filled to the top, I will place my finger at the bottom, so the water does not leave and gas bubbles will start to form. Afterwards I will turn it upside down and place it carefully into the trough.
- I will try and stop the stopwatch right on the 30 Cm3 of gas mark, so that the test is fair.
- I will be always using the same measuring cylinder water measuring the acid and water.
Concentration of Nitric acid – if the acid is diluted with water it would make it weaker and also slower to react with the limestone of Calcium Carbonate and because there are less particles of the reactant between the water molecules, which would have enabled it to make more collisions and therefore react quicker. Where as if the solution has a stronger concentration with less water or none at all it would react at a faster rate, this is because there will be more of the particles reacting and colliding at a more faster rate than a solution with a weaker concentration and a large surface area.
Safety
- A pair of goggles will be worn during the experiment, because the acids are very dangerous to the eyes and skin.
- When using the acid I will handle with care, because it is a harmful product to your body
- I will have to watch the boiling tube when I out the limestone in, because sometimes, the reaction is very fast, and suddenly the liquid falls out of the top.
- The limestone can be very small, and I will have to take care while holding the limestone.
- During the experience I will ensure that I have got the right clothing on and a safe working space, also I will always be standing up during the experience.
Fair test
To keep this experiment a fair test, all the variables need to be constant to prevent getting wrong results. The type of size of the limestone needs to be kept the same throughout the experiment; also I will use 5g of limestone in each concentration of acid. The acid cannot be using again after the reaction; otherwise there would be little reaction for the limestone. Before I start the next concentration, I will have to always clean the boiling tube out, because there will be bits of limestone and acid still at the bottom. For my result to be accuracy and this experiment to be fair, I must aware of the surrounding and what happening around me.
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Results
N/A – Did not react quicker enough, it took about 10 minutes, therefore it was not suitable, and also this would affect my graphs and my conclusion. So I and my partner decided not to put this result in.
Analysing Evidence
Graphs
All graphs are on separate pieces of graph paper at the end of the section.
Graph One
From looking at my graph you can quite clearly see that there is a trend occurring in all three sets of results. You can see that the highest concentration of acid, which is 1M, has the fastest rate of reaction. As the concentration of acid decreases then you can easily see that the rate decreases therefore the concentration decreases.
The only way of explaining this trend is by using the ‘Collision theory’ as followed: The higher the concentration means more collisions. If the solutions are made more concentrated it means there are more particles of acid colliding with water molecules. The increase of concentration makes the two particles colliding higher. If particles are more likely to collide they are more likely to react. In this case the higher the concentration of acid the higher the chance of the reaction between the limestone and the acid.
In this graph I have circled three main anomalous results.
Graph Two This graph is my average where I have found the average for all the three sets of results. I believe this graph is the best one, because all the plots lie on my curve. You can clearly see that there is trend. Again the way of explaining this trend is ‘Collision theory’ as mention before.
You can see that the highest amount of concentration is 1M, which also has the quickest rate of reaction. The lowest concentration of acid is 0.3M, and the rate is very slow on this certain concentration, and if we lower then 0.3M I think that the reaction would not happen.
Graph Three This graph about the rate of reaction, I got the reaction by one divided the time. As you can see if you double the concentration of acid you will double the rate of the reaction.
The higher the concentration of acid, the quicker the rate of reaction. Again ‘Collision Theory’ helps me explain this because, the higher the concentration of acid, the more chance of acid particles colliding with limestone particles, therefore the quick rate of reaction. The lower the concentration the less chance of the acid particles colliding with limestone particles, therefore the slower rate of reaction.
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Conclusions
From looking at my results and graph I am able to conclude that the more concentrated the acid the quicker the reaction happened. There was a dramatic change in the amount of seconds it took to collect the gas as more water was added to the solutions. For example, if you look at the graph it shows how much longer it takes for the gas to be collected in the second half of the concentrations than the first half. I find this hard to explain.
As I look at my results, the more diluted the solution is the longer it takes for the gas to collect. Before I did the experiments I made some predictions they were that the more concentrated the acid was the quicker the reaction would happen and more carbon dioxide would be produced. I was completely correct because what I thought would happen
At this point I was able to answer my main hypothesis which was “how does changing the concentration of acid affect the rate of reaction between Nitric acid and the limestone”. The answer to this would be that changing the concentration of the acid will either make it go slower or quicker and more or less gas would be produced depending on whether the concentrations were more or less. These factors affect the number of collisions of the particles, and this effects the rate of the reaction. If the number of collisions per second increases then the rate of the reaction will increase. This makes collisions between the particles more likely to happen. Therefore there will be more collisions per second, so more particles reacting per second. In other words, the rate of the reaction is increased.
Overall this was a very successful experiment, everything went very smoothly, that was why my results were very good, and I am able to make a conclusion like this.
As I repeated the experiment 3 times and worked out the average rate of reaction in each test, I think my results are quite reliable. However, I could make further improvement by increasing the number of tests and taking the results with a smaller gap. I could also increase the amount of limestone to more than 5g and change the amount of acid to 50ml; which would increase the reaction and will allow me to take more accurate results, as it would decrease the number of anomalous results.
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Evaluating evidence
I think that my observations and measurements were very good because I had a lot of pre experiment preparation including the preliminary time I was given so that I could practice my experiment; therefore I knew what to do. From this time I had been given to practice, I made sure before the real experiment that I had prepared everything properly. As a result I was doing the experiment correctly. This is why I think my observation and measurements were good.
I had Four main anomalous results throughout my whole experiment, the main one which stands out was on graph three, on the react of reaction, this happened at 0.8M, there are many reason might this have happened, I believe that this reaction was to fast compared to the rest.
I think the anomalous points occurred because of the following reason: -
- Human error, I probably didn’t stop the stopwatch exactly on the 30 Cm3 of Carbon dioxide, or the wrong amount of limestone added or the wrong amount of acid or water added.
- However there was only one anomalous result and the rest look good, I think that my results were fairly accurate (obviously apart from the anomalous result) kind of experiment.
I had a problem with my method in that I had to drop the limestone into the boiling tube, place the bung into the top and start the stopwatch. This is very a long sequence of activities to do in a certain amount of time. There is a potential for error here. I think this is the reason for the anomalous results as I did not start the watch at the correct time as I had trouble putting the bung into the boiling tube. I had a problem of the gas having to push the water down the delivery tube before the gas was collected. This added time onto the true time taken. This means my results are higher than they should be, because I started the stopwatch when I put the limestone into the boiling tube.
I think that my results are good as I was expecting far more anomalous results, but I only got the four. From this I think that my results are good enough, but there is always room for improvement and I think I could improve my results by decreasing the chances of human error which would mean I would have to be alert throughout the whole experiment so that I can try to stop these anomalous results, and if I can then I will be able to get the best results, I would do this by repeat any strange results.
To extend my enquiry I think that I could use a different variable, such as temperature, or surface area etc. This would get more evidence as I could investigate if temperature or surface area made any difference to the rate of reaction.
To provide more evidence for my investigation I could use a thermometer to measure the temperature during the experiment. For further investigation I could use stronger acid to see if there is limit to how quickly the reaction can take place. Also, I could measure the mass loss of the reaction by having the boiling tube on a top pan balance. I could take away the mass at regular intervals from the original and find out how quickly the reaction takes place.
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