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Investigate how changing the concentration of hydrochloric acid affects the rate of reaction between hydrochloric acid and calcium carbonate.

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Chemistry Coursework Rates of reaction Rates of Reaction Aim: To investigate how changing the concentration of hydrochloric acid affects the rate of reaction between hydrochloric acid and calcium carbonate. Hydrochloric acid + Calcium Carbonate = Calcium chloride + Carbon Dioxide + Water 2HCl CaCO3 CaCl2 CO2 H2O Introduction: As part of my chemistry GCSE course, I will be investigating the rate of the above reaction. I will use scientific knowledge to help me understand the science behind the reaction and I will also conduct a preliminary experiment to find out suitable measurements of reactants to be used in the main investigation. This will help me to conduct a fair test and also make sure I can get accurate results. Scientific Knowledge As this investigation revolves around the rate of a reaction, it is important that I understand how and why reactions can be sped up or slowed down. Chemical reactions occur when particles collide with enough energy (activation energy) to knock out outer electrons from their shells. There are four factors that can change the rate at which this happens; * Concentration * Temperature * Catalysts * Surface area The rate of a reaction can be measured by finding out how quickly a product is formed , or by finding out how quickly a reactant is used up. In this case, we will be measuring how much gas (carbon dioxide) that is being produced. We will measure this by using water displacement. As gases are less dense than water, they will float upwards through water, we see this as bubbles. If we filled a measuring cylinder full of water and channelled our carbon dioxide into it, the gas would displace the water making it possible for us to see how much gas is being produced. Now I will look at how the four factors can affect the rate of a reaction. Concentration: Increasing the concentration of a liquid speeds up a reaction because it increases the number of particles in that liquid, without changing its volume. ...read more.


After carrying out all of my preliminary experiments, I have found out suitable measurements for the reactants. They are: * 2g medium calcium carbonate chips * 50 cm3 hydrochloric acid Now I have collected the measurements I need, I can now begin to conduct my main experiment. Safety Whilst carrying out my experiment, I must take steps to ensure my safety. I must take care when pouring the stronger acids as they can be corrosive, and must also wear safety goggles so that acid cannot get to my eyes. This will ensure I carry out a safe experiment. A fair test? To get accurate and reliable results, I must make sure that my investigation is fair. Fist of all, I am changing the independent variable (the concentration of the hydrochloric acid) and measuring the dependent variable (volume of gas produced). I must keep every other possible variable the same. This will make sure that in each experiment, the conditions are the same. I will also repeat each experiment 3 times so that I get reliable results. Taking these steps will ensure that I get good results so that I can make a firm conclusion based on my prediction. Prediction Based on my background information and the knowledge I gained from doing my preliminary experiments, I predict that as the concentration of hydrochloric acid increases, so will the rate of the reaction. This is based on that there will be more particles in a higher concentration and so there is a much higher chance of a collision and a reaction. I also predict that if I double the concentration then the reaction should be twice as fast. This is logical, as there will be twice as many particles for the chips to react with and so there should be twice as many collisions. This was also the main trend in my preliminary experiments and so under a more precise environment, the results should show a similar trend. ...read more.


* We also had different people doing different jobs on the different days that we did the experiment. One person might have done their job differently to another and so that may have varied the results we got as well. If we kept the same person doing each job then our results would have been more reliable. * We could have also used a wider range, e.g. we could have timed the reaction for 2 minutes which would have given us more results to analyse. * The acid used may have been slightly different from day to day as the lab technician has to water down a stronger concentration to get different dilutions. Acid on one day could have been weaker than the day before but this is out of our control, as we are not allowed to dilute our own acid. Overall our results were fairly reliable as we repeated each experiment three times; repeating them even more probably would not have made much difference. Accuracy could have been improved, as I said above in the list, but with the given equipment and the school limitations we probably could not have done it much better. I could have expanded my experiment by fully investigating the change in the rate of reaction under different variables, like the ones in my preliminary experiment. This would have given me a broader understanding of how changing variables can affect the rate at which things happen. The results I did obtain were sufficient enough to support my first prediction, and, as I have decided that they were fairly reliable, I can be quite sure that I was right. However I obtained little evidence to support my second prediction. This may be because it was incorrect or because the faults in the experiment were more exaggerated than normal. Although I predicted wrongly once, another experiment may have shown differently. I did prove the expected trend which shows that my experiment was reliable and of reasonable quality and so I think that I was fairly successful in what I did. Harry Metcalf ...read more.

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