Also I could have changed the volume of the acid to see if it would make a difference.
As prelimary work I first started off with 10 of acid and 2g of calcium carbonate. At fist the reaction very quick and in 1min I had collected 100cm of carbon dioxide. So this was too fast so I changed to 1.5g of chips. The reaction in the 3mins collected nearly 180cm of carbon dioxide. So by the end I went to 1g of chips and in the 3mins I produced 130cm of gas which was a good amount, but it meant that as I lowed the concentration I would get amount of gas that could be read off the measuring cylinder as it would be a big amount and not a very small one, like if I had gone below 1g. Also I would not have to change measuring cylinder because one was full. So I had now an amount of chips, which meant that as I lowed the concentration I would get the gas collected in one cylinder, which could be read.
The first time I did the experiment I did it in a beaker to see what happened. I saw that there was a gas being produced so I decided to collect it. So I collected it by using a delivery tube and an upturned measuring cylinder. Also I conclude that I would do repeats to get some accurate data.
I predict for this experiment that as the concentration goes down the yield of gas will be slower over the 3mins and the amount will get smaller as it takes longer to produce. Also I can predict the max range for my 2 molar concentration by doing some mole calculations using the mass of the calcium carbonate. I think that be the end of the experiment the rate will slow down and produce a curve as the reaction slows down. Also I can go the same by getting the number of moles there will be of Carbon Dioxide. The problem is that it will only give the total yield of the experiment when the reaction has finished and not the result after 3mins.
CaCo + 2HCL CaCL + H O + CO
Mass
1g Moles= mass
100 RMM
=0.01 molar
Rtp x 0.01
= 24000 x 0.01
= 240
Volume
Moles= Vol =0.02 x 24000
- x concentration = 480
10x2
1000
= 0.04 moles of CO
The method I was that I put 10ml of HCl into a test tube and then added the 1g of marble chips (Calcium Carbonate). Then I waited 3mins and I took reads of the gas every 30 seconds. After that I would then do a repeat and then change the concentration of the acid. This was done as shown
1 molar= 5 of acid and 5 of water =10
1.5 molar= 7.5 acid and 25 water =10
0.5 molar= 25 acid and 75 water =10 etc
Apparatus
I have done 7 concentration of the acid and in the 7concentration I have taken results over 3mins. My result have been taken at 30s, 1min, 1.30mins, 2mins, 2.30mins, 3mins. So there I have done 6 results, which can be plotted on a graph. I have done a repeat for all the 7 concentrations so that I could get an average result, which will give me in theory some more accurate results and so I could plot it as one line on a graph.
I tried to make it a fair test by trying to be accurate with all my measurements and to check the apparatus to see if there were any leaks, like with one experiment where there was a leak in the delivery tube and so the amount of gas getting to the cylinder was smaller. Also trying to get a cork, which would fit the test tube, was another problem. So I controlled the size of the crystal by every time getting small crystal, but I could never get them all the same size, but I hardly think it would affect my results. They would only be affected if the crystal were really too big. The volume and the weight were controlled by being accurate and take time to get the right amounts. The temperature I could not control, but the temperature in the room stay about constant so it did not affect the experiment. I used the same acid from the same batch we were given.
The safety measures taken were to wear safety specs and the hydrochloric acid is an irritant and harmful. So we stood up while working and we did not splash the chemicals around and we cleaned up if some were spilt and the same with broken glass. While the experiment was in progress we stood away from it.
Obtaining Evidence
I change my method first by doing more concentrations, I did more concentration so I could give a bigger range of results and so that I could compare the result better as there would be a clearer pattern by doing more test. Also I did some repeats so I could get an average result do I could plot it as one line on the graph. I will measure to the near whole number and to no decimal place as it will be easy to read of cylinder and the margin of error is reduced. The evidence is as reliable as I could get it with the apparatus. Also with the fact that there will be soon human error in the experiment and so it is not all down to the apparatus. As you can see by the table below there are lots of readings and so there should be sufficient data. As you can see from the results I did lots of results between 1-2molar because there was lots of gas being produced and so I need to do more result because it would show mistakes, but also that the amounts of gas would tail off.
Analysis
As we can see on the graphs we have a line, which tails off slowly. In some graphs this is more obvious. On the 2 molar graph the line hardly tails off so there is still a lot some time to go in this reaction. For 1.75 the gradient stay about constant until we get to 2 mins where we can see that it is starting to tail off. For 1.5 the steep gradient is the same until 1min when then the line starts to tail off and then by the 3mins mark we are stating to near the end of the reaction. For 1.25 the steep gradient is constant until 1min and then again tails off rapidly and by 3 mins the ration has nearly finished. The way the gradient changes can be seen by the transect lines on the graphs. It is the same for 1&0.75&0.5 the line at the start is at a steep but constant gradient and after the 1min the gradient start to get shallower and so the reaction slows down.
So why did we get the result of the line starting to tail off by the end of the 3 mins. As the concentration in the experiment was deceased the amount of gas being produced in the 3mins went down. This is because as the concentration is reduced the amount of acid particles in the solution will have been reduced. So this means that there will be less collision happening with the calcium carbonate so there will be less successful (bonds are broken and new ones are formed) reactions and so less gas produced in the 3mins, but the reaction will take longer as there an not many acid particles, but in what ever amount of time it takes it should produce the same amount of gas, but over a longer time period, this will depend on what substance is in excess as said in the planning. We get the tailing off on the graph because after some time, there are fewer calcium carbonate atoms, and also the acid is less concentrated by the end. So the reaction will slow down with there being fewer collisions and so the graph will tail off, it will have then a shallower gradient than at the start. This can been seen on the graph by seeing if there is a steep gradient the reaction is very quick and the rate of reaction will be high. The shallower the gradient the slower the reaction and the rate of reaction will be low.
As you can see my predictions were spot on as by using my scientific knowledge. As from the results of the mole calculations, my results are well under the mole result, which shows that I did my experiment right, but it shows that after 3mins, that the reaction is only just half way through. We can see that as I predicted the yield of gas is less as the concentration goes down. Also that as experiment neared the 3mins the graph started to curve off with the gradient getting shallower as predicted.
Evaluation
The measurements taken were as accurate as I could get with the apparatus, the result should have been accurate as I did a repeat of all the results. As you can see by the results the results were mostly accurate. As they produce the right type of line and the point on most graphs were on the line. The result showed that the experiment gets slower when it nears the 3mins.
The main anomalous result was that the 1.25 molar results produce less gas than the 1molar result. I think this was the case because the measurements here had to be very accurate and only be a cm out could affect the result. Also having crystals of a bigger surface area could have affected the result. As there surface would be smaller and on a smaller surface there are less collisions, so less reactions and to slower production of gas and so less gas over the 3mins. I had a problem that day finding the right sized bung so it could also have been a problem, as gas may have escaped. Another main anomalous result was the 0.75 molar repeat. The results were 6 to 10 cm of gas out every time, which is to do with the same reasons as above.
One big problem was collecting the gas, because as it had to be full of water it was hard to put an upturned cylinder into the water without losing some water and so making the results less accurate and not reliable. The chip sizes were all different so I could not get a constant surface area so it meant that this would affect my result, as the amounts of gas would be different.
The temp of the room could not be control so this may have affected the experiment, but I think the temp was about constant though out the experiment. The chip sizes were all different, but I tied to get the smallest chips so getting a bigger surface area. The way I changed the concentrations meant that the concentrations were not 100% correct so the result cannot be 100% accurate and reliable.
There was a good amount of data produced and the only way of getting a better conclusion is by doing more repeat, but also get better apparatus e.g. more accurate and reliable.
The improvements are that the corks fit the test tubes so that gas will not escape. Also get chips, which are about the same size. Better way of collecting the gas more accurately.
The extension work can be that we use different acids to see the difference between them. Also we could see how heat affects the experiment. We could also do different surface areas to see which one will produce the most gas in a certain time limit. We could final to higher concentrations such as 3 and 4 molar to see the differences.
