Catalyst:
A catalyst gives the reactants a surface to stick to where they can collide with each other. This definitely increases the amount of collisions. Also, catalysts increase the rate of reaction by helping break chemical bonds in reactant metals and provide a ‘different pathway’ for the reaction.
Plan:
For this investigation, I will change the concentration of the hydrochloric acid. I will be measuring the rate of reaction by recording the amount of hydrogen gas given off using a gas syringe.
To make this investigation fair, I will have to keep the other factors the same. Because of the factors that affect the rate of reaction above, I will have to keep the temperature of the acid and surface area of the magnesium the same. I will keep the temperature the same by leaving the all the acid in the lab for a day before I use them. This will ensure that all the acids will be at room temperature. Also, I must not use a catalyst or use a catalyst for all of them and use the same amount. Furthermore, I must use the same type of acid because it is the hydrogen in the acid that hits the magnesium so even though I use two types of acid that are both 1 molar, H2SO4 is twice as reactive as than HCl because it has 2 hydrogen atoms to give whereas HCl only has one to give. I will also have to keep the amount of acid, the amount of magnesium and the equipment I use the same to make the investigation a fair test.
Prediction:
Because I am going to increase the concentration, I predict that as the concentration increases, the rate of reaction also increases. This is due to the fact that concentration increases the rate of reaction because the frequency of collisions will also be increased.
Preliminary experiment:
For me to decide what the best volume and concentration of hydrochloric acid and mass of magnesium is, I conducted a pilot experiment. I decided that magnesium ribbon was best to use because magnesium powder reacted too fast which will make it hard to record results. I also decided increasing the acid molar by 0.5 is best because it doesn’t give me very big changes or very little changes. I thought the appropriate volume of hydrochloric acid to use is 10cm3 and a good amount of magnesium ribbon to use is 0.66g. I also thought using hydrochloric acid ranging from 0.5 to 2.5 molar is suitable.
The magnesium ribbon had to be sanded using sand paper to make it more reactive. This is because magnesium is very reactive and it pulls oxygen atoms from the air which oxydises it. The oxidised magnesium didn’t react as well as the sanded magnesium so I will have to sand all of the magnesium I use when I repeat my experiments to make it a fair test.
Equipment:
- Conical flask
- Bung
-
10cm3 measuring cylinder (to make it as accurate as possible)
-
100cm3 gas syringe
- Stop watch
- Electronic balance that’ll give me reading to the nearest 0.01g for accuracy
- Hydrochloric acid molars 0.5 – 2.5
- Sand Paper
- Magnesium ribbon
- Clamp stand
Safety:
For safety reasons, I will need to wear a lab coat and goggles. This is to prevent any acid getting into my eyes and onto my clothes. If I get any acid on me, I must wash it off immediately with cold water to stop it from burning my skin.
Method:
I am going to assemble the equipment I need and then measure 10cm3 of hydrochloric acid. I will start from 0.5 molar and then increase it each time by 0.5 molar until I get up to 2.5 molar. I wouldn’t start from 2.5 molar because there will be a little bit left in the conical flask after I pour it out and that would affect the next experiment which would be 2.0 molar making it slightly more concentrated. If I wash out the conical flask, there would still be a little bit of water left and I cannot ensure every bit of water is out and the conical flask is completely dry. So I will start from a low concentration and increase it because a low concentration wouldn’t affect a higher concentration.
After I have got my 10cm³ of hydrochloric acid, I will pour it into the conical flask. Then I will sand and weigh my magnesium ribbon to get 0.66 grams. After that, I will put the magnesium into the conical flask and quickly put the bung on top and start the stop watch. I will then record the amount of hydrogen gas collected in the gas syringe every 5 seconds.
Once the magnesium has gone and the reaction is over, I will repeat the experiment 3 times and calculate the average to make my results more reliable and trustworthy. My results will be more accurate because I can compare the results I get with the previous results and if there is a big difference then I will know something went wrong in one of the experiments.
Obtaining:
Analysing:
I plotted my averaged results onto graphs to easily see the trend in the results. I also put all the molars onto one graph for easy comparison.
The graphs of my results show that as the concentration of acid increases, so does the rate of reaction. This is because there are more particle collisions so there would be more successful collisions. The graphs show the rate of reaction by the slope of the line. The higher or steeper the slope, the faster the reaction is. My prediction is correct and my results support the theory because the theory is; as the concentration increases, the rate of reaction increases. However, one of the trend lines does not support the theory and my prediction. That is the 2.5m trend line. This is because it should be steeper than the 2.0m trend line to show that the rate of reaction is faster. Also, the first 10 seconds of all the reactions are best because it shows the initial collisions. After that, the rate slows down as the reactants are being used up. Then the graph starts to become horizontal as all the reactants are used up. However, for the 0.5 molar graph, it shows that the rate of reaction doesn’t slow down towards the end.
Evaluating:
My results seem consistent and accurate because when I repeated the experiment, I got results that are close together. Most of the sets of results fit a pattern. However, the 2.5 molar and 0.5 molar results do not fit the pattern. I think it is because the gas syringe got stuck and wasn’t able to fill up with hydrogen smoothly.
I think the 2.5 molar results can be excluded from my conclusion because of the gas syringe. I think more gas would’ve been collected but the gas syringe wasn’t able to fill up that quickly. Furthermore, how long it took for the reactants to be used up shows that the 2.5 molar had the fastest rate of reaction. Also, all the other results support the theory.
The method could be improved by using a gas syringe that opens out more smoothly or putting oil on the syringe to lubricate it. Overall, I think this method was suitable even though I had an anomaly because it still shows me the trend and rate. I think the results I got for molars 0.5 – 2.0 are reliable because the rate increases each time the molar increases. Also, I repeated my experiment to get more reliable data. However, my results aren’t accurate because I should be getting the same amount of hydrogen produced for all of the experiments I do. This is because I am using the same amount of magnesium and hydrochloric acid. The only thing that should change is how quickly the hydrogen gas is being produced. This is probably due to the gas syringe not working properly.
For further work, I could use sulphuric acid instead of hydrochloric acid. Sulphuric acid which is H2SO4 should have a rate which is twice as fast if I use the same amount of magnesium because it provides twice as many hydrogen atoms. If the rate of reaction increases as the concentration of sulphuric acid increases, then it will support my prediction and conclusion of this experiment.