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# Investigating how the concentration of acid affects the rate of reaction between hydrochloric acid and calcium carbonate (marble chips)

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Introduction

﻿Investigating how the concentration of acid affects the rate of reaction between hydrochloric acid and calcium carbonate (marble chips) Hypothesis: As the concentration of acid increases, the rate of reaction between marble chips and hydrochloric acid increases. Explanation: The higher the concentration of acid, the more often collisions between marble chip particles and hydrochloric acid particles will occur. By increasing the concentration per unit volume of acid, there are more hydrochloric acid particles than water particles so marble chip particles can react frequently therefore increasing the frequency of collisions. This would make it more likely to get successful collisions. These factors would increase the rate of reaction. According to the collision theory, reactant particles have to collide in order for a reaction to start. However not all the collisions are successful and if there is not sufficient energy, the molecules will simply rebound. I expect the rate of reaction to be proportional to the concentration of acid in the first few minutes if the practical, e.g. doubling the concentrations of the acid should double the rate of reaction; therefore my results should show that the reaction rate at concentration 1.0mol is half the rate of reaction when the concentration of the acid is 2.0mol. The reaction rate should theoretically decrease as the reaction progresses. This is due to the reaction time increasing as the number of HCl molecules present decreases as they react with calcium carbonate molecules to produce calcium chloride, water and carbon dioxide. Although carbon dioxide escapes into the air, the water produced will dilute the acid, so the concentration of HCl will decrease. There will be fewer successful collisions due to the decrease of HCl molecules. This reaction is exothermic reaction energy is released to the surroundings because more energy is released making bonds in the products than is needed to break bonds in the reactants. Here is the balanced equation for this reaction: CaCO3(S) ...read more.

Middle

81.56 690 133.09 125.30 133.54 138.17 81.55 720 133.09 125.30 133.5 138.16 81.55 750 - - 133.52 138.16 81.55 780 - - 133.51 138.16 81.55 810 - - 133.50 138.16 81.55 Results Table showing the amount of carbon dioxide gas produced at each concentration of hydrochloric acid in grams Time (s) 0.5 molar 1 molar 1.5 molar 2.0 molar 2.5 molar 0 0 0 0 0 0 30 0 0.02 0.04 0.04 0.07 60 0 0.05 0.10 0.09 0.16 90 0.01 0.09 0.15 0.15 0.26 120 0.02 0.12 0.21 0.21 0.35 150 0.03 0.16 0.24 0.25 0.42 180 0.04 0.18 0.29 0.29 0.47 210 0.05 0.20 0.31 0.33 0.52 240 0.06 0.22 0.35 0.36 0.56 270 0.07 0.23 0.37 0.39 0.59 300 0.08 0.24 0.39 0.42 0.62 330 0.09 0.25 0.42 0.44 0.65 360 0.09 0.27 0.43 0.46 0.67 390 0.09 0.28 0.45 0.47 0.68 420 0.10 0.28 0.46 0.48 0.70 450 0.11 0.29 0.47 0.50 0.72 480 0.11 0.30 0.49 0.51 0.74 510 0.12 0.31 0.50 0.52 0.75 540 0.12 0.31 0.51 0.53 0.76 570 0.12 0.31 0.52 0.54 0.76 600 0.12 0.31 0.52 0.54 0.77 630 0.12 0.32 0.52 0.55 0.77 660 0.12 0.32 0.53 0.56 0.78 690 0.12 0.32 0.54 0.57 0.78 720 0.12 0.32 0.55 0.57 0.78 750 - - 0.56 0.57 0.78 780 - - 0.57 0.57 0.78 810 - - 0.58 0.57 0.78 Table showing the average mass of CO2 lost against time (secondary evidence) Time (seconds) Average amount of CO2 produced for each concentration of HCL (g) 0.2 molar 0.4 molar 0.8 molar 1.2 molar 1.6 molar 2.0 molar 0 0.00 0.00 0.00 0.00 0.00 0.00 5 0.0400 0.0800 0.0600 0.107 0.127 0.137 10 0.0567 0.0933 0.0967 0.177 0.233 0.253 15 0.0600 0.103 0.1367 0.237 0.317 0.367 20 *0.0567 0.117 0.157 0.290 0.390 0.473 25 0.0733 0.120 0.193 0.340 0.477 0.590 30 0.073 0.133 0.217 0.403 0.547 0.680 35 0.0800 0.147 0.243 0.450 0.623 0.773 40 0.0900 0.163 0.270 0.487 0.703 0.850 45 0.0967 0.167 0.290 0.543 ...read more.

Conclusion

However, the marble chips were still producing CO2 (marble chips were still fizzing). I think that we should have continued each concentration to around 20 to 25 minutes in order to see if there will be a further change in mass. This could have helped us to obtain a wider and more reliable set of results. We only performed one practical for each concentration of HCL. We could have conducted repeats for our separate concentrations and averaged those results in order to get very reliable data. The more reliable results would have strengthened the conclusion made from my hypothesis. Strengths: We strictly followed the control variables. For example: we kept the mass of marble chips and the volume of HCL the same. This minimised most problems in our method. We used the same make of apparatus for every concentration. This meant that each experiment with different concentrations of HCL were similar. The entire experiment was conducted in the space of two days resulting in a reduction in scope of errors (like temperature). In addition, we dipped the thermometers in each HCL acid and observed if there was any temperature change. Since a change in temperature would affect the rate of reaction, it was essential that this variable was controlled. The results were taken correct to 2 decimal places. This meant that the results obtained were accurate. The apparatus was handled carefully and the practical was conducted smoothly. This helped us avoid any unnecessary accidents or breakages. I have looked through my primary data and I found a few points which did not fit my lines of best fit. These points have been circled on my graphs. My anomalies were at: 0.5mol: 390 and 460 seconds 1.0mol: 150 seconds 1.5mol: 210, 630, 660 and 690 seconds 2.0mol: 30 seconds 2.5mol: nothing These anomalies may have occurred because of misreading of the mass at any particular time. The several of the anomalies aren?t very major so the presence of anomalies will definitely not change my hypothesis or my conclusion. ...read more.

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