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  • Level: GCSE
  • Subject: Science
  • Document length: 3672 words

Calcium carbonate reacts with dilute hydrochloric acid according to the equation below

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Introduction

Calcium carbonate reacts with dilute hydrochloric acid according to the equation below. CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O (l) + CO 2(g) You are to confirm by experiment that this reaction is first order with respect to hydrochloric acid. Introduction The order of reaction gives the relationship between the rate of reaction, and the concentration of acid. In a first order reaction the rate is directly proportional to the concentration of the acid. Second order reactions are where the rate of reaction depends on the concentration squared. The aim of this experiment is to prove that the reaction that takes place is a first order reaction. Finding the rates for different concentrations, and plotting the results on a graph, rate against concentration, and drawing a line of best fit will be used to prove this. Prediction I predict that in the relationship between the reaction rate and the concentration, they will be directly proportional to each other. This means that it will be a first order reaction. I have predicted this because page 4 of 4B2.5 states that in a reaction where the rate is directly proportional to the concentration of acid, it is a first order reaction. Equipment 2 molar hydrochloric acid marble chips electric weighing scale 250ml conical flask 50ml measuring cylinder stop clock Method 1. Take the equipment and set it up, placing the conical flask on the scales 2. Press the tare button on the scales so that it shows that the weight is zero 3. Weigh out 10g of marble chips into the conical flask 4. Measure out 50cm3 of hydrochloric acid (this is 73.0g dm-3) 5. Pour the acid into the conical flask and note the weight 6. Start the timer as soon as possible 7. Record the weight every 15 seconds for two minutes 8. Repeat this experiment for every tenth percentage (43.8g dm-3 = 30 ml acid, 20ml water)

Middle

Mass (g) Change in mass (g) Mass (g) Change in mass (g) Mass (g) Change in mass (g) 0 62.59 0.00 59.34 0.00 62.68 0.00 15 62.41 0.18 59.30 0.04 62.61 0.07 30 62.27 0.32 59.16 0.18 62.51 0.17 45 62.13 0.46 59.04 0.30 62.40 0.28 60 61.99 0.60 58.95 0.39 62.31 0.37 75 61.90 0.69 58.83 0.51 62.20 0.48 90 61.79 0.80 58.74 0.60 62.12 0.56 105 61.68 0.91 58.64 0.70 62.04 0.64 120 61.62 0.97 58.60 0.74 61.97 0.71 Concentration 51.1g dm-3 Mass of marble chips: 10.02g Mass of marble chips: 9.99g Mass of marble chips: 10.00g Time (seconds) Mass (g) Change in mass (g) Mass (g) Change in mass (g) Mass (g) Change in mass (g) 0 59.13 0.00 66.73 0.00 62.03 0.00 15 59.01 0.12 66.71 0.02 61.90 0.13 30 58.90 0.23 66.64 0.09 61.81 0.22 45 58.79 0.34 66.58 0.15 61.69 0.34 60 58.69 0.44 66.52 0.21 61.59 0.44 75 58.57 0.56 66.46 0.27 61.50 0.53 90 58.50 0.63 66.38 0.35 61.41 0.62 105 58.41 0.72 66.34 0.39 61.33 0.70 120 58.33 0.80 66.26 0.47 61.26 0.77 Concentration 43.8g dm-3 Mass of marble chips: 10.03g Mass of marble chips: 9.99g Mass of marble chips: 9.98g Time (seconds) Mass (g) Change in mass (g) Mass (g) Change in mass (g) Mass (g) Change in mass (g) 0 59.79 0.00 59.34 0.00 62.86 0.00 15 59.73 0.06 59.31 0.03 62.71 0.15 30 59.64 0.15 59.26 0.08 62.60 0.26 45 59.56 0.23 59.21 0.13 62.49 0.37 60 59.49 0.30 59.15 0.19 62.40 0.46 75 59.39 0.40 59.09 0.25 62.29 0.57 90 59.32 0.47 59.04 0.30 62.22 0.64 105 59.27 0.52 58.99 0.35 62.15 0.71 120 59.19 0.60 58.93 0.41 62.08 0.78 Concentration 36.5g dm-3 Mass of marble chips: 10.00g Mass of marble chips: 10.00g Mass of marble chips: 9.98g Time (seconds) Mass (g) Change in mass (g) Mass (g) Change in mass (g)

Conclusion

This created anomalous results, which could be eliminated by redoing the experiment under more controlled conditions. The anomalous results may have occurred for many reasons, however, during this experiment the temperature conditions were a major issue. The experiment was conducted on several different days, when the temperatures varied greatly. One day the experiment was carried out whilst it was snowing. This caused a massive temperature drop, and also a change in the atmospheric pressure. When the temperature increased, the molecules would have moved around faster. This means that there would have been more collisions between the molecules, increasing the rate of reaction. However, when it got colder, it would have been the opposite. The molecules would have moved around slower, causing fewer collisions, therefore the rate of reaction would have been slower. The method I used meant that the size of the marble chips varied. Although I weighed about 10g of marble chips, it was often impossible to ensure they weighed exactly the same amount. By trying to make the weight of the marble chips 10g, I changed the size of the marble chips, using some big and some small. Using marble chips of different sizes meant that they did not have the same surface area. This will have affected the results I have collected, as there would have been different amounts of surface area upon which the molecules could collide. This is a limitation of the method, and therefore makes the reliability of my method questionable. If I were to conduct this experiment again, I would try to improve these aspects of the experiment, to eliminate anomalous results. I would aim to conduct the experiment under more controlled conditions. I would carry it out on the same day, to ensure that the temperature was as similar as possible for each of the experiments. Also, as well as weighing the marble chips, I would try to find a way to ensure that the surface area of the chips was similar.

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