Amount of gas evolved
I could use a gas syringe to collect the gas that will evolve from my experiment. I could use these results to calculate the initial rate of reaction.
The weight before and after the experiment
I could put the conical flask with the chosen volume of hydrochloric acid onto a set of accurate electronic scales and record the weight of it. I could then drop a piece of magnesium into the conical flask and measure the decrease in weight at chosen intervals. The weight of the experiment will decrease because as the hydrogen in the hydrochloric acid is being displaced it is being released and will float up and out the conical flask, the weight change will not be very big, but there will be one.
How long the magnesium takes to dissolve
I could measure the length of time it takes for the magnesium to dissolve. The only problem with recording my experiment this way is that I could only calculate the average rate of reaction and not the initial rate of reaction
Ways to measure the rate of the reaction:
Average rate of reaction
Initial rate of reaction
I will be using the initial rate to calculate the rate of reaction as it can calculate the true rate and not the average rate of reaction.
Factors
The factors that could affect the rate of reaction of my experiment are as follows:
· Concentration of acid
This could affect the rate of reaction because the higher the concentration of the acid then the more acid particles per 100cm3 so more collisions per second and then there will be more successful collisions per second.
· Surface area of the magnesium
If the magnesium had a bigger surface area each time the experiment was done, then the acid particles will have a bigger area to collide with, so more collisions will occur every second and the more collisions per second than the more successful collisions per second.
· Type of acid used
If you changed the type of acid then the rate of reaction would change. Hydrochloric, Sulphuric and Nitric acid all would produce a different rate of reaction, so if I do change the type of acid then all three kinds would produce a different set of results.
Key factor
I have chosen to use the concentration of the acid as my factor that I will change. I chose this because several different concentrations can be made up before the experiment by the lab technicians and they will be able to make them accurately.
There will be several different concentrations of acid, which will give me a wide range of results, which will be reliable and reproducible.
Prediction
My prediction is that the higher the concentration of the acid then the higher the rate of the reaction will be. I am saying this because of the collision theory. The higher the concentration of acid then the higher the number of acid particles present per 100cm3 of acid. This means that there will be more collisions per second, which means there will be more successful collisions per second, so the rate of reaction will increase.
If I double the concentration of the acid from 1M hydrochloric acid to 2M hydrochloric acid then I will expect to see the rate of the reaction double. This is because there are twice as many acid particles in 2M hydrochloric acid than in 1M hydrochloric acid, so there will be twice the amount of collisions per second and because there are twice the amount of collisions per second then there will be twice as many successful collisions per second, increasing the rate of reaction.
Plan
I am intending to react with a chosen length of magnesium ribbon with a chosen volume of hydrochloric acid. I will measure the rate of reaction by collecting the hydrogen gas that is produced in a gas syringe that will be connected, via a piece of rubber tubing and a rubber bung to the conical flask that the reaction will take place. I will quickly drop the length of magnesium into the flask and connect the rubber bung to it. I will then start the stop clock and record the volume of gas evolved every 5 seconds for 15 seconds. I have chosen these times because I only need three results as I am going to measure the initial rate of reaction and not the average. I will repeat each experiment so that my results are reliable and reproducible.
Fair Test
In order to keep my experiment a fair test I will have to make sure that I keep the following factors the same:
· Starting temperature of the acid
· Volume of acid used (cubic centimetres)
· Surface area of the magnesium
· Clean the magnesium with emery paper before experiment
· Length of magnesium
I will also have to make sure that the gas syringe is correctly connected and that it is placed quickly and tightly enough so that no hydrogen gas escapes.
The following factor that I will change is:
· The concentration of the acid
Apparatus and chemicals used
The apparatus and chemicals used during my experiment are as follows:
Chemicals
· 1M hydrochloric acid
· 1.5M hydrochloric acid
· 2M hydrochloric acid
· 2.5M hydrochloric acid
· 3M hydrochloric acid
· 3.5M hydrochloric acid
· Distilled water
Apparatus
· Measuring cylinder (100ml, 50ml, 25ml and 10ml)
· Conical flask (250ml and 100ml)
· Safety glasses
· Beakers (200ml and 90 ml)
· Test tubes
· Test tube rack
· Gas syringe
· Tile
· Paper boat
· Ruler
· Thermometer
· Scissors
· Glass rod
Safety
The things that I will need to do to keep my experiment a safe one for myself and other students around me are as follows:
· Wear safety goggles as I am using concentrated hydrochloric acid
· Care to eyes and the skin besides all the other people is always vital and necessary
· Care in using glassware since it is sharp when broken and can cut skin
· Safe disposal of reagents and laboratory chemicals
· Care when returning all used glassware and equipment at the end of the experiment
Preliminary work
The preliminary work that I will be conducting is to find out the optimum length of magnesium ribbon and the optimum volume of hydrochloric acid.
To do this I will be measuring out a volume of hydrochloric acid and a length of magnesium ribbon and reacting them together. If there is still some magnesium left over when it has stopped effervescing then I will have to increase the volume of hydrochloric acid.
If the reaction takes too long to finish then I will have to shorten the length of magnesium that I use, however if the reaction is too short then I will have to do the opposite and increase the length of magnesium that I use. The optimum rate that I am trying to find is a reaction that isn‚t too short but isn‚t too long, so I can get enough results to plot a good graph. I need to find the optimum volume of hydrochloric acid so that it is in excess after the reaction is over.
Apart from trying to find the optimum rate of reaction I also have to find out how to keep the temperature change down. This is because as the reaction is taking place the temperature will rise because the reaction is exothermic, and this could cause my results to be inaccurate as the temperature change will heat up the acid and give the acid particles more energy so they will move faster and collide with the magnesium with greater force causing more successful collisions per second.
To show that the hydrogen gas is not being given of from the water in the hydrochloric acid I will have to conduct a control experiment. This is when I will try to react magnesium with distilled water to show that there is no reaction between magnesium ribbon and water and that the hydrogen gas is evolving from Preliminary results.
After my preliminary experiments I discovered that if I used 50cm3 of hydrochloric acid with 3 cm of magnesium ribbon then I could obtain some good results.
Also with these quantities the temperature change is kept to a minimum
Time (seconds) 5 10 15
Gas evolved for 1M hydrochloric acid (cm3) 4 7 11
Gas evolved for 2M hydrochloric acid (cm3) 18 24 24
Starting temperature (oC) End temperature (oC) Temperature change (oC)
22 25 3
As these results produced a reasonable volume of gas in a reasonable time these were the quantities of chemicals that I used.
I also used these quantities of chemicals because it kept the temperature increase to a minimum.
Method
1. Put on safety goggles
2. Collect clamp stand, clamp and boss
3. Collect conical flask and measuring cylinder
4. Collect stop clock
5. Measure out 50 cm3 of 0.0M hydrochloric acid with the measuring cylinder
6. Pour hydrochloric acid into the conical flask
7. Collect thermometer
8. Measure the starting temperature of the hydrochloric acid
9. Measure 3cm of magnesium ribbon
10. Clean the surface of the magnesium with the sandpaper
11. Drop the magnesium into the conical flask
12. Quickly place the rubber bung into the conical flask
13. Start timing with the stop clock
14. Record the amount of gas evolved every 5 seconds for 15 seconds
15. Measure the temperature of the solution after the reaction is over and measures the temperature change
16. Repeat steps 5 to 12 changing the concentrations of the acid
17. Repeat steps 5 to 15 to make sure that my results are reliable and reproducible.
Conclusion
My results table and graph show me that when I increase the concentration of the hydrochloric acid, the initial rate of reaction also increases.
Altogether I tested 5 different concentrations of hydrochloric acid. 0.0M, which was the lowest concentration of acid that I used, there was no reaction. 2.5M hydrochloric acid, which was the highest concentration that I used, produced the fasted rate of reaction. I repeated all 5 concentrations twice to be sure that they were reliable results and in all cases the higher the concentration the higher the rate of reaction. I had stated this in my prediction.
However I also stated in my prediction that if I doubled the concentration from 1M to 2M hydrochloric acid then the rate of reaction will also double. I have discovered that this is not the case.
Interpretation and Evaluation:
In this experiment I found out that many different factors including; Concentration, Temperature and Surface Area affect the rate of reaction. For the experiment I found out that the higher the concentration of the acid the quicker it takes to dissolve the magnesium. I know this because the more acid molecules that is in the beaker there is more chance of a successful collision to take place. Another factor that I learned is that the rate is constantly changing during the reaction because as time goes on there are fewer acid molecules. There are fewer acid molecules because when the acid reacts the same particle cannot react again, so there are less to end with than there are to start with. As time goes on the number of acid particle decrease so there is less chance of a successful reaction to take place.
Before I started the experiment I made up a prediction. I predicted that the more concentrated the acid solution the faster the magnesium and hydrochloric acid will react. I thought that this would happen because when there are more acid particles in the test tube the more chance there is of a successful collision. I was right in my prediction but I did not predict that the rate of reaction slows down as time goes on which did happen in my experiment.
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