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An Investigation into the effect of Acid Concentration on the Rate of Reaction

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Introduction

An Investigation into the effect of Acid Concentration on the Rate of Reaction Introduction: We are going to investigate the effect of Acid Concentration on the Rate of Chemical Reaction. We are going to use the combination of Hydrochloric Acid and Calcium Carbonate as the reactants: Calcium Carbonate + Hydrochloric Acid Calcium Chloride + Water + Carbon Dioxide Prediction I predict that the greater the concentration of acid the greater the rate of chemical reaction i.e. the rate of reaction will be directly proportional to the concentration of acid. This means that if I were to double the concentration of acid the rate of reaction would also double, halving the time taken. In order to generate a more accurate picture I have constructed a series of graphs highlighting my above statements. I have used a relative scale, following my prediction, in order to calculate the rate and therefore time taken. Concentration (Molar) Rate Time Taken 2.0 5 0.2 1.6 4 0.25 1.2 3 0.8 2 0.5 0.4 1 1 This graph shows the concept of how the greater the acid concentration the greater the rate of reaction. The idea being that with a concentration of 0 moles the rate would be infinity, comparatively by increasing the concentration of acid, the more instantaneous the reaction becomes. This graph represents the relationship that exists between acid concentration and rate; by increasing the acid concentration the rate is increasing as well. The straight line indicates the direct relationship; double the acid concentration you double the rate of reaction. Justification The Collision theory justifies the prediction of increased acid concentration causing increased rate of reaction by relating to the concept of proportional molecular content; i.e. if there are more acid molecules they are more likely to collide with those of the Calcium Carbonate molecules: The diagrams above illustrate the greater likelihood of a collision in 2.0 molar concentrations due to the higher concentration of acid. ...read more.

Middle

How we intend to control these factors is shown below: Controlled Variables Independent Variables Dependant Variables Temperature Acid Concentration Time Taken Volume of Acid Volume of Gas produced Mass of Calcium Carbonate Surface Area pf Calcium Carbonate Light Intensity Use of a Catalyst Pressure After we had planned our experiment out thoughts turned as to how we would present our results. We constructed a design for our table of results: Acid Concentration 1 Time (s) 2 Time (s) 3 Time (s) 4 Time (s) 100% (2.0 molar) 80% (1.6 molar) 60% (1.2 molar) 40% (0.8 molar) 20% (0.4 molar) Acid Concentration Average Time (s) Observations 100% (2.0 molar) 80% (1.6 molar) 60% (1.2 molar) 40% (0.8 molar) 20% (0.4 molar) Results Acid Concentration 1 Time (s) 2 Time (s) 3 Time (s) 4 Time (s) 100% (2.0 molar) 11.0 8.0 9.0 8.0 80% (1.6 molar) 12.0 10.0 Anon: 21.0 9.0 13.0 60% (1.2 molar) 16.0 Anon: 23.4 14.0 15.0 9.0 40% (0.8 molar) 21.0 24.0 26.0 25.0 20% (0.4 molar) 50.0 43.0 Anon: 60.0 47.0 48.0 Acid Concentration Average Time (s) Observations 100% (2.0 molar) 9.0 Effervescence occurred when the Calcium Carbonate was added to the acid solution. The rate of effervescence decreased as the experiment went on, also the gas syringe moved slower as the experiment went on. At the end of the lower acid concentration experiments there was a white solid which stuck to the bottom of the conical flask. 80% (1.6 molar) 11.0 60% (1.2 molar) 16.0 40% (0.8 molar) 24.0 20% (0.4 molar) 47.0 Conclusion The Graph Acid Concentration vs. Time Taken shows a curve, reflecting the graph of our prediction. It shows that as acid concentration doubles the time taken halves. The gradient of the graph is changing (decreasing as the x axis unit increases) the reason for this is because as acid concentration doubles the time taken will halve, this is justified because there are more acid molecules available to react with the Calcium carbonate creating a large chance of collision. ...read more.

Conclusion

Limitations The obvious limitations came with the ability to truly control the controlled variables (although this seems not to have affected the results). On top of this the pattern given by the results on the graph would extend to higher acid concentrations and lower acid concentrations, something which I was not able to test. This could provide further evidence, even problems with my conclusion. It also may be an idea to look at other variables and their relationship with acid concentration on the affect of rate of reaction. For example, it may be that the affect of a increased acid concentration might be greater at a greater temperature or pressure. This I feel is an important limitation, although I remain satisfied with the truth of my conclusion/ Further Work As I have mentioned above I feel it a limitation to the simplicity of our experiment. I feel it would have been of importance in surmising the affect of acid concentration and rates of reaction to have the knowledge of how other factors would affect this e.g. varying other variables or the amount of gas evolved. In respect of a greater collection of gas, I feel that this would be important as I predict that the rate of reaction would decrease within a reaction, something which is not able to be accounted for in my simple reaction. This concept is backed up by f observations of a decrease in effervescence as the experiment continued, however this is not quantifiable, therefore not firm evidence. The further varying of other variables (as I have already mentioned) I feel would be of importance as it would show where the effect of acid concentration on the rate of reaction stands in comparison to others; looking at how some work best in conjunction with others or not - a case for further study. As we noted earlier certain factors were not able to be controlled precisely. Therefore given further time it would be relevant to test these factors, controlled specifically, in order to see by just how much they affected our experiments, if at all. 1 BMD ...read more.

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