Reactions between HCL and Marble chips.

increase. I will be investigating the effect of concentration on the rate of a reaction. If a solution is made more concentrated, then there are more reactant particles per set volume. This makes collisions between the reactant particles more likely. Therefore there will be more collisions per second and as a consequence, more particles reacting per second. In other words, the rate of the reaction is increased. The reaction I will be investigating is: Calcium carbonate + Hydrochloric acid Calcium Chloride + Water + Carbon Dioxide The balance equation for this is: Ca Co3 + 2HCl ? H20 + C02 Before the apparatus was set up the experiment had to planned as fairly as possible. This involved only changing one variable at a time, therefore all the other variables had to be kept constant. Firstly the mass of the chips was kept as similar as possible, I did this by weighing the chips to be at an approximate mass of 1.4g on a top pan balance. From a previous experiment I did involving different sized marble chips I found that the surface area greatly effects the rate of reaction, therefore I tried to find marble chips of roughly the same size. Another variable I took into account was the volume of HCl I will use; I am changing the amounts of acid in each concentration. I could not control the room temperature but I assumed that the room temperature would stay around the same for the duration of the experiment. The temperature would affect the concentrations of the acid. I will start timing the collection of the gas when I replace the bung on top of the conical flask. After deciding how to approach all of the variables in the experiment I decided how to carry out my experiment. I decided to use different concentrations of HCl in my experiment, these are them-: 50cm3 acid- 0cm3 water, 40cm3 acid- 10cm3 water, 30cm3 acid- 20cm3 water, 20cm3 acid- 30cm3 water, 10cm3 acid- 40cm3 water. To obtain these results I then measured and recorded how. I predict that the solution with the high concentration of acid will have a much faster rate of reaction than the weaker solution. I have predicted this from my knowledge of a previous experiment and scientific knowledge. I think that this happened because the more HCl in the solution the greater the concentration and there will be more particles colliding and more energy and therefore a faster rate of reaction. The reason I think that the rate of reaction will increase is that the experiment is exothermic, this means that it will give itself more energy and therefore more collisions and faster collisions. Therefore I predict that the rate of reaction will increase with the concentration of the HCl solutions. Obtaining Evidence Concentration (Acid and Water) Time Taken (In seconds) 50 cm3 and 0 cm3 61 40 cm3 and 10 cm3 85 30 cm3 and 20 cm3 127 20 cm3 and 30 cm3 200 10 cm3 and 40 cm3 618 Analysing Evidence and 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; this is shown by the black dotted lines. 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. This was completely correct because what I thought would happen, did. At this point we are able to answer our main hypothesis which was æhow does changing the concentration of acid affect the rate of reaction between hydrochloric acid and calcium carbonate. 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 reactant 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. If a solution is made more concentrated, then there are more reactant particles per set volume. This makes collisions between the reactant particles more likely. 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. Evaluation I feel that this was a successful experiment. My results seem to indicate a clear pattern from which I was able to confidently draw a conclusion. This conclusion confirmed my hypothesises. The method produced results accurately and quickly enough to finish the experiments in the allotted time. My results were reliable, as the experiment was a fair test. I ensured that this was true by keeping all of the variables not involved in my experiment constant. These were the presence of catalysts and the starting temperature of the reactants. I could not control the temperature at any time in the reaction except for at 0 seconds. This is because the reaction released thermal energy. I can say that no other energy was deliberately put in or taken out of the contents of the conical flask during the experiment. I used roughly the same weight and three chips of roughly the same size throughout the whole experiment, this kept the surface area constant, but something unexpected happened. I had a problem with my method in that I had to drop the marble chips into the conical flask, place the bung into the top and start the stopwatch. This is such a long sequence of activities to do in the time it takes the marble chips to hit the surface of the solution. There is a potential for error. I think this is the reason for the abnormalities in my results as I did not start the watch at the correct time as I had trouble putting the bung into the conical flask. I have already mentioned the 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. The truth of my conclusion is not undermined by this however, as the same effect happened to each test. I could overcome this problem and the one mentioned in the previous paragraph by only starting the timer when the gas starts to fill the measuring cylinder. This would not include the time taken to push the water down the delivery tube in my results, and I would not have to start the stopwatch at the same time as putting the marble chips in the flask. To provide more evidence for my investigation I could use a thermometer to measure the temperature during the experiment, this would show whether my theory of the lower concentration not heating up the reactants is true or not. 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 conical flask 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. To be sure I can rely on my results I will repeat he experiment twice or three times if necessary, because there is chance of inaccurate results for many reasons. I will use acid of 0.5, 1, 2, 3, and 4 molar concentrations.