Chemistry: Practical Investigation
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Chemistry: Practical Investigation Aim To see how varying the concentration of hydrochloric acid affects its reaction time with calcium carbonate. CaCo3 + 2HCl CaCl2 + H2O + CO2 Apparatus In this experiment I will need: Hydrochloric acid, calcium carbonate, water, conical flask, a bung with hole for tube, burette, water basin, eye protection, stopwatch. Background science "A reaction rate is the speed at which reactants are converted into products in a chemical reaction. The reaction rate is given as the instantaneous rate of change for any reactant or product"1. Collision theory is the theory that atoms or molecules need to collide to react. Most, if not all, reactions also need activation energy for the reaction to occur, also orientation is needed. Factors affecting collision theory are surface area, catalysts, temperature and concentration. Surface area affects the rate of reaction because it increases the frequency of collisions as there is more to collide with, temperature affects the rate of reaction because it both increases the frequency of collisions and the energy in the collisions as it excites the atoms, while concentration affects the rate of reaction because it also increases the frequency of collisions as there are more atoms to collide into the calcium carbonate.
Once done repeat the experiment using different concentrations of HCL (diluted with water) with ratios of acid: water as shown:- 1:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9. I decided on using a burette instead of a boiling tube or measuring cylinder because a burette is more precise and accurate, this is also the reason why I used a stopwatch instead of counting. Despite this they are not 100% accurate so some error margin in produced. Factors involved in this experiment include temperature, concentration and surface area. The factor I have decided to change is concentration. I will be able to change this factor by diluting the hydrochloric acid with water and I will keep the other factors the same by monitoring the temperature to keep it at a steady rate and by weighing the large chips of calcium carbonate each time so the experiment is fair. I use large chips because it is a slower reaction and so will leave less room for human error. I will use 10 different concentrations to increase the range of results and I will repeat the experiment three times for concentration to ensure any outliers can be found and discarded so to make sure that the data I will collect will be accurate and reliable, leading to a good quality of evidence on which to base my decision.
Trends seen from the graphs show a positive correlation however it is not proportional meaning that the rate is affected greater at higher concentrations compared to lower concentrations and thus reaction gets faster towards the end, making the gradient progressively more. Conclusion From this experiment I can conclude that the concentration of an acid does have an effect on the rate of reaction because of collision theory. Evaluation Due to human and apparatus error then the concentration has ~0.05cm3 error, while the rate has an error of ~ 1 second and 0.5cm3 The results aren't proportional due to many factors. This experiment is exothermic and so the temperature increase may affect the results, also there is no way to get precisely the same surface area of calcium carbonate as they weren't pre-cut to specification. The level of confidence in the results is low because of the many outliers in the lines of best fit because of this the data is insufficient and unreliable. Ways in which I could improve the experiment and results would be to carve out calcium carbonate chips to a specific surface area, while using a cooler to effectively reduce the temperature increase caused by the thermal energy being transferred.
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Here's what a teacher thought of this essay
This report is fairly well written, supported by some strong scientific theory. Specific strengths and improvements have been suggested throughout.
Marked by teacher Cornelia Bruce 17/04/2013
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