Prediction: I predict that as I increase the concentration of acid, the rate of reaction will also increase. This is because the higher the concentration of acid the more particles there will be to react with the marble chips. Increasing the rate of reaction. The rate of reaction will slow down when the concentration of water is increased because there will be more water particles then of acid reacting with the marble chips.
Conclusion:
The results for 50ml acid and 0ml water.
(Table………………….)
My graph for the reaction of 50cm acid and 0cm water shows that the reaction was at the same rate of reaction throughout, I can tell this because the line is completely straight and is very steep. The reaction started off slowly, but then went into a steady rate of gas production. There is one anomalous result, on the third test at 50 seconds gas production increases out of line with the rest of the results. The marble chips may not be entirely pure; meaning that some parts would take longer to dissolve than others. When the line increases this may be due the marble not being pure and the acid is able to dissolve the marble more quickly than usual. Or that the marble chips in one or two of the tests were smaller. The graph for the reaction of 40cm acid and 10cm water shows that the reaction started off quickly and towards the time of 1:00 and 1:10 minutes, the line increases in steepness. This is because the rate of reaction increased, allowing the marble chips to be dissolved more quickly. This may be because the marble was ‘softer’ on the inner layers and the acid was able to break them down more quickly. The first test in these concentrations has a slower rate of reaction, but also has a high increase in the line. This also occurs between the time of 1:00 minute and 1:10 minute. This may be due to the events as explained above. The graph is also much lower and longer than the others are, this is because the pieces of marble were bigger in the first experiment than they were in the second and third. This means that there is a much smaller surface area in which the acid can react, so not as much gas would be produced. The graph for the results of 30ml acid and 20ml show the reaction is steady and fairly quick. The reactions start off slower than they finish, so the marble chips were being dissolved more quickly towards the end then they were at the beginning. The graph which shows equal amounts of 25ml acid and 25ml water has a slow reaction rate at the beginning but then fastens as before towards the end. There is one unusual reading in the second test, the reaction rate suddenly increases then carries along at the same rate for the rest of the time, this occurs between 40 and 50 seconds. An outside factor may have caused the jump, temperature would increase the rate of reaction because more energy would be given to the acid particles causing them to move more quickly which would give them a bigger chance of hitting with the marble. The graph showing 20ml acid and 30ml water is gradual and the second test line actually evens out showing where the reaction is beginning to slow. The first test must have had small chips because the reaction was faster and in less time. The third test may have had larger chips forcing the reaction to slow down. The results showing the 10ml acid and 40ml water are very slow and gradual. The difference in finishing time is quite large suggesting the size of the chips differed. The first test is steeper and reacts more quickly than the other two tests, may be due to a larger chip size. Comparing them all on the single graph allows me to get a bigger picture and makes it easier to compare them. Apart from the 10ml acid and 40ml water, all other results are close together and are quite straight. With a best fit line the results of 20ml acid and 30ml water sows a curve, this means the rate of reaction started of slowly but became faster towards the end. The line showing 25ml acid and 25ml water shows that towards the end the line begins to level off. This means that the reaction was slowing down, there are no marks on the final line because a test finished before the others I could then no longer take averages with just two sets of results. There is a large gap between the line of 20ml acid and 30ml water and the line of 10ml acid and 40ml water, this is due to the amount of acid in the water. There are much less acid particles in the solution, which means the particles would collide as often. This line should be following the pattern of the other results; it should be nearer to the previous line, The concentration of the acid is going down evenly so in theory so should the results.
Evaluation: Overall my investigation was good, because it was safe and produced fairly accurate and reliable results. The anomalous results I have pointed are mostly due to the chip size. But other factors may have affected my results. The temperature in the room may have risen while we were in there making the reaction speed up. To make sure the temperature would be the same for all experiments I would have to monitor the temp. of the room often and if necessary would put the conical flask into a beaker of water that I would control the temp. of. Due to human error I may have measured the wrong amount of water or acid. To resolve this I could use a larger measuring tube that, I would then be able to see the measurements more clearly. To make the test a fairer, I could try and make the size of the chips the same, although this is almost impossible, since all marble chips are different. To make my results more accurate and reliable I could repeat the experiment a total of five times or more. The reaction could have speeded up due to human error because the conical flask could not have been washed out properly. So some acid could have been left in the beaker, making the reaction speed up. Then making my results incorrect. To extend upon my investigation I could try the reactions at different temperatures. I could then find the optimum temperature for the reactions to take place at. I could also try different acids such as sulphuric acid and nitric acid; I could then compare the results and ascertain which acid reacts more quickly with the marble.
