Coursework - Investigating rates of reaction
Aim: To see what effects changing the concentration of hydrochloric acid will have in a reaction between magnesium and hydrochloric acid.
Prediction: The higher the concentration of acid, the faster the rate or reaction will be.
Info: The phrase "rate of reaction" means "how fast is the reaction" or "the speed of the reaction." Rates of reaction can vary from very slow reactions such as rusting to very fast reactions such as magnesium dissolving in hydrochloric acid (the investigation I am doing). There are things that can speed up reactions; they are called catalysts, which can be a transition metal or an enzyme which reduces time to save money. There is a rate equation to show the rate of reaction, it is:
The overall order of reaction is given by (a + b), a or b usually have values such as 0, 1 or 2. If the order of reaction is 0, then as the concentration increases, the rate will not be affected; If the order of reaction is 1, then as the concentration is doubled then so is the rate; If the order of reaction is 2, then as the concentration is doubled then the rate is multiplied by 4. This can be applied to the area of investigation because it can show how the rate of reaction is affected by different orders of reaction and it directly affects the rate of reaction, as shown in the equation above.
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Equipment: Gas Syringe, Timer, 100 cm3 beaker, clamps and stands, delivery tubes, 100 cm3, conical flask.
Step 1: Set up the equipment, then measure out the correct volume of acid to water, which will vary, and measure out the correct length of Magnesium ribbon, this will ensure the test is fair.
Step 2: Place the Magnesium ribbon in the conical glass, pour over the water/acid solution and start the timer, record the amount of gas produced every 30 seconds for 5 minutes, e.g. 30, 60, 90, 120, 150, 180........seconds etc.
Step 3: Record the results in a table, then once the 5 minutes has expired, change the ratio of Hydrochloric acid/water, for example instead of putting 25 cm3 of water and 0 cm3 of acid, change it to put 20 cm3 of water and 5 cm3 of acid, this will make it a fair test because it has the same overall volume but a lower concentration of acid. Repeat this process.
Results: The original method that I did was flawed in some ways, so after doing some preliminary results I decided to alter the method so that the experiment would be fairer. As the preliminary results show, 2 minutes is not enough time to get the results needed, so it was changed to 5 minutes. Also the length of magnesium ribbon used was too long, which either made the reaction go too fast with a high concentration or the reaction went on for too long with a lower concentration.
Concentration of Acid = 1 Mole
Conc. = Concentration
R.T = Room Temperature
Mg = Magnesium
From the results I can conclude that my prediction was correct. The higher the concentration of acid the faster the rate of reaction. This is shown visually in the graphs, when the concentration of Acid is higher the Magnesium reacts a lot faster and gets to a stop much quicker. As the concentration of acid goes down it starts the reach a stop slower, and in the end doesn’t reach a stop in the time given.
The results are reliable because they both show effectively the same thing: that the Acid reacts with the magnesium and produces gas at different speeds, depending on the concentration of acid, and then whether it is at the start or not within the time limit the gas will stop being produced. The results can also reliably show how the temperature affects the rate of reaction; the results show that on one day when the temperature was lower (20°C) the reaction slowed down, and on the day when it was hotter (24°C) the reaction sped up. Although the change in temperature was unexpected it was still recorded on both days, and the anomaly was explained. A way that could provide addition relevant evidence is to take another set of runs, but instead take 3, each one at different temperatures. This would effectively show how temperature and concentration can affect the rate of reaction.
The results taken show what were expected to be shown; although some anomalies did occurred. The first result of the second run was taken at a different time than the rest of the results from the second run, and as shown on the table, on the two separate days the room temperature was different. It therefore shows a more similar pattern to the results in the first run than the second run. There were only 2 runs taken, because the results from the first run were so successful and went so smoothly I thought a second run would only further show what I already knew, just make it more certain and reliable. This was so, except I didn’t expect the change in room temperature to affect the results as much as it did, it doesn’t make the results any less certain; it just shows how much the temperature can affect the rate of reaction. I recorded the results every 30 seconds for five minutes because I believed that five minutes was enough time for the reaction work fully, which in the higher acid concentration cases it was; I took results at 30 second intervals because this was enough time for a sufficient amount of gas to be produced, making it a fairer test. If I could have repeated this experiment again, I would have taken 3 runs with different temperatures for each, to show how much the temperature can affect the rate of reaction.