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How Concentration of Acid affects rate of reaction.

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Introduction

Chemistry Coursework - How Concentration of Acid affects rate of reaction Plan I shall investigate whether the concentration of an acid affects the reaction rate between an acid and a carbonate. I shall vary the concentration of acid, but keep the other potential variables constant. These include: * Time - if an experiment has longer to take place than another, unless the reaction has finished, differing the time over which the experiment will take place will distort the results. This is because it has longer to react. So there is longer for the reactants to come into contact with each other. I shall use a stopwatch to keep the time constant between experiments. * Heat - if the heat of the solution and/or chips is different between experiments, this will affect the result. Increased heat means that molecules are moving faster. This will lead to more molecules of acid coming into contact with the carbonate in the same timeframe. Crucially, it will also mean that more molecules collide with enough force to power a reaction. Both of these reasons mean that heat should be kept constant between experiments. Ideally, the conical flask should be placed in a water bath to regulate the temperature. However, due to time constraints, this was not possible, so I could not use water baths and had to rely on a constant room temperature. * Surface area of chips - if one chip has a higher surface area but the same mass, than another, and they are both placed in an acid solution, the chip with the larger surface area will come into contact with more acid molecules, so it will react faster as there are more possible areas for the reactions to take place. ...read more.

Middle

I chose these cylinders for the concentrations because they were the lowest measuring cylinders available for the amount of gas produced (including a little room for safety)). b) Thread tube from conical flask through pneumatic trough and into measuring cylinders. 3. Place plastic tray on scales and add 2.0g of 2-4mm calcium carbonate chips onto it (it is a good idea to 'zero' the scales onto the plastic tray) 4. Measure solution into 20ml measuring cylinder. For a concentration of 0.0M, 20ml of distilled water is needed. For a concentration of 0.4M, 16ml of distilled water and 4ml of 2.0M hydrochloric acid is needed. For a concentration of 0.8M, 12ml of distilled water and 8ml of 2.0M hydrochloric acid is needed. For a solution of 1.2M, 8ml of distilled water and 12ml of 2.0M hydrochloric acid is needed. For a concentration of 1.6M, 4ml of distilled water and 16ml of 2.0M hydrochloric acid is needed. For a concentration of 2.0M, 20ml of 2.0M hydrochloric acid is needed. Pour the solution into the conical flask. 5. Drop chips into conical flask, place bung on top and start stopwatch. 6. Monitor stopwatch and when it reaches 30s, look to see how much gas was displaced from the measuring cylinder and record this. 7. Clean apparatus and repeat steps 2-7 for different concentrations of acid. Other Notes I am measuring the amount of carbon dioxide produced. This is because it is the gas formed in this reaction: calcium carbonate + hydrochloric acid � calcium chloride + water +carbon dioxide. The strength of the acid is governed by the % hydrogen ions which dissociate. ...read more.

Conclusion

This would ideally have been in my experiment, however, due to time constraints I could not include it. I think I took enough measurements to the correct degree of accuracy and over an appropriate range, because I managed to find out that concentration2 is directly proportional to the initial rate of reaction. The results I took followed the line of best fit, so that suggests that they are accurate too. The experimental uncertainties are within acceptable limits as they follow the line of best fit closely. The only result I found which was not within acceptable limits, I retook and as it was anomalous, I disregarded it when drawing an average. I would change the measuring cylinder to a burette, for increased sensitivity and accuracy. I would also prefer to use powdered calcium carbonate, as there are no problems of surface area: mass ratio because the powder will have the same surface area: mass ratio (because the powdered chips are relatively the same size). However, in order to use the powder, an automatic stirrer would be needed to stop the powder clinging together. The acid should also be changed to one that disassociates less, in case the powdered calcium carbonate reacts a lot more than the small chips of calcium carbonate. It could also be useful to test some other concentrations of acid, especially ones which are a lot stronger, to see if the conclusion is valid for these values. Higher values have another advantage because any small error in the line when it is shown with small values of concentration will not be so pronounced, it could be due to experimental error. However, when the concentration increases, any small error in the line of best fit on the graph will be more pronounced. ...read more.

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