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To study the effects of changing the surface area on the rate of a chemical reaction
This hypothesis is based on the Collision Theory, where in order to react, the two particles involved must:
1. Collide with each other
2. The collision must be energetic enough to overcome the activation energy of the reaction
3. The collision must bring the reactive parts of the molecule into contact the correct way – they must collide with appropriate geometry (the reactive parts)
Considering that the surface area of a particle is a factor that mainly affects the collision rate of particles, it would be safe to assume that as the surface area increases, the reaction rate increases.
The graph should turn out to be something like this:
1. the reaction is the fastest at the start
2. The reaction is slowing down here
3. No more product is formed
Amount of product
What is manipulated
The time it takes for the reaction to complete depends on the surface area of the compounds being used, because it determines the rate in which the reaction will occur.
Volume of the gas collected (H2, CO2)
The amount of gas collected for each experiment will depend on the
1. Mass of Calcium Carbonate (both marble chips and powdered form)
2. Mass of Magnesium (both ribbon and powder)
3. Volume of Hydrochloric Acid
4. Apparatus Used
1. The masses of the substances utilized will remain constantly fixed during the experiment
2. 50 cm3 of HCl will be used for every trial – 550 cm3 in total
3. The apparatus used will remain the same throughout the whole experiment
Mg + 2HCl → MgCl2 + H2
1. Magnesium ribbon
2. Hydrogen Gas will be the gas collected
1. 3 Trials will take place
1. Mass of Magnesium ribbon in:
1. Trial 1: 0.064 grams
2. Trial 2: 0.063 grams
3. Trial 3: 0.065 grams
CaCO3 + 2HCl → CaCl2 + H2O + CO2
1. Marble Chips
2. Carbon Dioxide will be the gas collected
1. 2 Trials will take place
1. Mass of Marble Chips in:
1. Trial 1: 3.998 grams
2. Trial 2: 3.988 grams
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
1. Sodium Carbonate (Powdered)
2. Carbon Dioxide will be the gas collected
1. 2 Trials will take place
1. Mass of Sodium Carbonate
1. Trial 1: 0.504 grams
2. Trial 2: 0.505 grams
1. Eye-Protection – 1 pair of Safety Glasses
2. 1 pair of Scissors
3. 1 Electronic Scale
4. 1 Conical Flask (100cm3)
5. 1 Single-holed rubber bung and delivery tube to fit conical flask
6. 1 Measuring cylinder (100cm3)
1. 12cm of Magnesium Ribbon
2. 550 cm3 of Hydrochloric Acid
3. Marble Chips
4. Sodium Carbonate (Powdered)
1. Set up apparatus as shown
2. Fill the conical flask with 50cm3 of HCl
3. Insert the end of the syringe into the hole on top of the stopper
4. Add the magnesium ribbon
5. Seal the flask with a rubber stopper as quickly as you can, at the same time have someone else present to start the stop watch once the magnesium ribbon has been added to the hydrochloric acid
6. As the reaction takes place, note down the time it takes for the gas collected to reach a multiple of 5 (i.e. 5mL, 10mL ….50,55,60,65 etc)
7. Keep measuring until the reaction has stopped, or you are unable to measure anymore
8. Repeat each experiment 3 times, just to be sure the data collected is accurate
9. At step 4, replace the underlined compound with the next compound after one experiment is completed
Magnesium Ribbon – Mg + 2HCl → MgCl2 + H2
Trial 1 (0.064 ± 0.005 grams)
Time (in seconds) ± 0.05 s
Volume (in cm3) ± 2.5 cm3
Unfortunately I was unable to create a graph using time as the independent variable, because the lab that I had utilized did not have the equipment available to accurately to record the data if time were to be the independent variable. Another factor that played into my decision was the fact that the smallest calibration of the glass syringe I used was 5 cm3. Since the only visible measurements shown on the syringe were multiples of 5, it would only seem reasonable that I switch around the variables, making time the dependent variable, and the volume collected the independent variable, since I couldn’t exactly measure how much gas would be collected every 5 seconds; otherwise the relationship the graph would depict would be completely incorrect.
As you can see on the graphs, the slightly steep slopes show when the reaction is the quickest, as it should be in the beginning. The curve shows the reaction slowing down, but unfortunately the curve continues. This is because the reaction is still taking place. I was unable to record the rest of the data because the measuring tools that were available weren’t able to record to such a high degree. In some cases though, like in the powdered sodium carbonate experiment, the reaction began so quickly that I wasn’t able to record the time in most cases, so I just stuck with those that I had managed to note down. In other cases, there were so many distractions in the lab that it was difficult to remain focused. My classmates kept removing some if the items that I was using.
The idea was to see how the rate of reaction changed when the surface area of a substance was increased. Initially, my plan was to react magnesium ribbon and magnesium powder with 1 mole of Hydrochloric acid; so I could compare and contrast how the surface area of the substance affected the rate of reaction. I had planned to keep everything about the two substances the same. Its element, mass, the amount of Hydrochloric acid I was going to react with it; the only thing different would be its surface area. Unfortunately the Lab didn’t have any available. So I decided to do the same experiment to Calcium Carbonate, this time using marble chips and powdered calcium carbonate. To my dismay I found that the powdered calcium carbonate wasn’t reacting at all. So I had to change it to sodium carbonate.
There is skepticism about using different elements, seeing as they have different orders of reactivity. These factors, including the concentration of the acid used, could also affect the rate of reaction. However, the same acid concentration was used for all experiments, in all trials; so we can dismiss that. However, sodium is much higher up the reactivity series than calcium, which is higher up the reactivity series than magnesium. This is the problem with this experiment; the elements positions in the reactivity series could have really altered the rate of reaction.
However, the experiments still prove that when the surface area of a substance is increased, the rate of reaction increases as well. This happens because, when two substances react only the surface particles of the substances can come into direct contact with the reactant particles. Increasing a substance’s surface area, like turning big solid chunks of calcium carbonate into powder, leaves more solid particles available to react. The more particles available to react at one time, the faster the rate of the reaction.
Only atoms on the surface can react
If you break the substance down, more
atoms are exposed and ready to react.
Considering the lack of material available, I think I was able to manage the experiment fairly enough to produce results. However, I am not pleased with the factors that may or may not have affected my results, and the circumstances in which I had to switch my variables around. Therefore I would like to state a few things I would like to alter, if ever I got the change to do this experiment again.
1. Next time, instead of using a stopwatch, I would like to use a digital device, like a laptop for example, that was somehow connected to the glass syringe, which was programmed to record the volume of the gas collected every 5 seconds. This time the graph would turn out the way it should be.
2. Instead of using a measuring cylinder, I would replace it with a burette, as it takes more accurate measurements of liquids.
1. Chemicals Used
1. I would try and used the same element next time; the only difference would be the surface area. For example, if I used magnesium, to study the effects of surface area on the rate of reaction, I would only you magnesium ribbon and magnesium powder. Studying different elements with different reactivity’s would dismiss any data already collected because an element’s position on the reactivity series may also determine the rate of reaction. Use the same element.
1. Amount of People involved in the experiment
1. If I had to do the experiment again, with the same apparatus, I think I would like to have 3 people participating in the collection of data. 1 person would be watching the syringe rise and call out to record whenever it rose, the 2nd person would time it, and the 3rd person would record it. This time, the data may be even more accurate, because no one is taking their eye off the experiment, like I was doing during my experiment just to record data.
I feel that altering these aspects of the experiment would increase the level of accuracy, as to get more substantial data to calculate the order of reaction. Unfortunately with the data I have so far, I am unable to derive the concentrations of the substances I had utilized in my experiment. However, as the objective was to investigate whether or not different surface areas affected the rate of the reaction, I think that I have produced enough data to support my theory.