I predict that as the surface area increases, the speed of the reaction will increase therefore the gas will be produced faster. I believe this because most chemical reactions happen faster when there is more of the reactant to react with. When there is a larger surface area, there is more of the reactant available which makes it easier for them to react together. Usually, when the surface area is doubled it will double the rate of reaction.
Chemical reactions take place by chance. Particles need to collide with enough velocity so that they react. As the surface area is increased the particles have a bigger surface to react with so more molecules can react at a time. This means that they are colliding more often and there is a bigger chance that the collisions have enough velocity to cause a reaction. Since there are more collisions the chemical reaction takes place faster.
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The outcome of my graph, I think will look something like this
In my experiment the variables to be kept constant, The temperature will be kept constant at room temperature, The amount of acid will be kept constant at 10ml,The concentration of the acid will be kept constant at 2mol/dm3, The amount of magnesium ribbon will be kept constant at 10mm by 2.5mm. I must make sure that we use the same size, amount and roughly the same mass of magnesium. I want to keep the magnesium the same throughout the experiment so that it will be a fair test and the results will be in relation to each other, otherwise they will be completely different and it will ruin the experiment. I must also make sure that we take our readings at the same intervals throughout the experiment i.e. I will take a reading after the Mg has dissolved and disappeared. I will carry out the experiment 3 times, as this will increase the accuracy of my results.
* As I will be dealing with acid, safety goggles are essential
* If it should happen that the acid is spilt, it should immediately be wiped up.
* The acid should be handled with care because once it has made contact with skin it can cause irritation.
- Magnesium ribbon
- Hydrochloric acid
- Metal stand
- Burette (to ensure accuracy)
- Water
- Scissors
- Ruler
- Test tube
- Test tube rack
- Measuring cylinders (10 cm, 20 cm) – for HCL
- Stopwatch
To decide on the best mass of magnesium a number of calculations were done and a pilot experiment conducted.
We were advised to use roughly 0.05g of magnesium ribbon (found to be 1 cm long). The Relative Molecular Mass (RMM) of magnesium is 24, therefore the moles of magnesium to be used was:
Moles= 0.05
24
Moles= 0.0020833
It was decided to use an excess of hydrochloric acid to ensure all the magnesium reacted, therefore 10ml of acid was used in the pilot experiment. At room temperature 10ml of hydrochloric acid was added to 0.05g of magnesium and the time taken for it dissolve was recorded.
The procedure for the experiment is as follows;
* Using a measuring cylinder, measure 10ml Hydrochloric Acid (HCL) an pour it into a test tube
* Measure 10mm of magnesium ribbon and check on the balance that it weighs roughly 0.05g.
*Using a hammer to make sure there are no other ways the HCL can get onto the ribbon, bend the ribbon into a line of the desired length.
*Drop it into the test tube
* Repeat experiment two more times (for accuracy) and record all results in a table.
* Repeat the experiment for surface areas for the 2nd strips, 3rd strips, 4th strips, 5th strips, and 6th strips.
It is important that only the surface area is changed since this is what is being investigated.
I have chosen to use a 100ml measuring cylinder to measure the volumes of substances used. I will use a ruler to make sure exactly 10mm of Mg ribbon is used each time.
I have chosen to repeat the experiment 3 times because it therefore allows me to calculate an average rate of reaction. This will ensure that there are no anomalous results and it will increase accuracy. It will allow me to see the increase in rate of reaction and 6 results should be enough to identify any trends.
I will start the experiment by putting on goggles for safety reasons, and I will also remove all items around me which could make me trip up of fall; avoid me having an injury. Then I will get a test tube rack and 4 test tubes preferably 6 test tubes so there isn’t an add result (an anomaly). Then fill up a burette with Hydrochloric Acid (HCL) up to at least 60ml. I will then empty some of the Acid from the burette because there might be some air trapped at the bottom of it. Then I will fill each test tube with Hydrochloric Acid (10ml) and then cut the magnesium into size. I will slice the magnesium strips at the length of 10mm for every test tube. From then on I will slice the pieces in to size,
and so on. I will do 6 different surface areas.
I will drop each Magnesium strips at a time so I can record the time for it to dissolve. I will drop the 1st strip into the 1st test tube, then the 2nd strips in the second and so on giving me results and time for the Magnesium to dissolve. For every Magnesium strip I put I will immediately start the stopwatch timing the Magnesium to dissolve until the fizzing comes to a standstill. Then on I will be left with a result table of the times it took the Magnesium to react with the Hydrochloric Acid. I have chosen to repeat the experiment 3 times because it therefore allows me to calculate an average rate of reaction. This will ensure that there are no anomalous results and it will increase accuracy. It will allow me to see the increase in rate of reaction and 6 results should be enough to identify any trends.
My graph shows that the greater the number of pieces more rapidly the Magnesium dissolves. My results prove this; it backs up my initial prediction. I was right!
Explanation
You can see from my diagram that the bigger surface area means the more Hydrochloric Acid particles can make contact with the Magnesium particles and react more to dissolve it more rapidly.
The equipment that I used to carry out the task, was suitable for example, when measuring small amounts of acid I used a 5 cm measuring cylinder. I took a precaution in making sure that I did not pour too much or too little of HCl, essentially to enable a fair test.
I believe that the experiment was successful, however some of the results were unreliable. However, this doesn’t affect my results since I am only concerned with the initial rate of reaction. The reason they may have lasted longer, could be the fact that there was a change in the length of magnesium someone could have measured the wrong amount, hence, causing the reaction to last longer. There was a change in acid, which could have caused it to last longer. Also the mishandling of equipment could have contributed in an anomalous result i.e. There might have been some trace of sweat from my finger on the magnesium while cutting or dropping it in the test tube. I may also have poured out different amounts of acids even though only small differences could have an effect.
In the graph, anomalous results have been identified. These could have been caused because the Mg strips could have stuck together causing the rate of reaction to slow down, thus, not giving accurate results. The way the experiment was managed could have affected the results - lack of attention at times could have lead to unreliable results. An error in plotting, drawing curves or calculating gradients in my graph could have also affected the calculated rate of reaction.
On the whole, my results obtained were reliable, they enabled me to draw a conclusion. The evidence, which I gathered, seems sufficient to support a firm conclusion, that is, the larger the surface area, the more chance of collisions taking place, therefore the faster the rate of the reaction.
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To improve the experiment and to make my results even more reliable, I could find a way of attaching and releasing the magnesium inside the test tube so that I can get an accurate count, not a second before and not even a second after dropping it into the acid without any time being lost/gained. The magnesium should be measured by its mass rather than length, as this is not always accurate due to different rolls of magnesium strips.
Another way in which the experiment could be improved is that I could take extra precautions i.e. Pay more attention to the experiment and not be distracted by others also before starting the experiment I should make sure that I have enough equipment – magnesium and acid so that I do not have to change as this may give me unreliable results. To further extend this experiment and get additional evidence for the conclusion, I could carry out a much more complex experiment where I could investigate other factors which may affect the rate of a reaction, that is, temperature, concentration, pressure, catalyst and light. This would help extend my knowledge into this topic.
