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.
· Temperature of the acid
If the starting temperature of the acid is different each time the speed at which the acid particles collide with the magnesium ribbon will increase more the higher the temperature goes. This means the acid particles move with more energy, which means they will collide with the magnesium with more energy, which will give 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.
Question
My question is to see that if I change the concentration of the Hydrochloric acid for each experiment I will see an increase or decrease in the rate of reaction between Hydrochloric acid and Magnesium ribbon.
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 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 react magnesium ribbon with distilled water to show that there is no reaction between magnesium ribbon and water and that the hydrogen gas is evolving from the hydrochloric acid when it is being broken down into magnesium chloride and hydrogen.
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 measure 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
Results
Raw results
A table to show the results for test 1
Time (seconds) 0 5 10 15
Concentration (Molar)
0.0 0.0 0.0 0.0 0.0
1.0 0.0 4.0 7.0 11.0
1.5 0.0 10.0 20.0 26.0
2.0 0.0 18.5 24.0 24.0
2.5 0.0 29.0 29.0 29.0
A table to show the results for test 2
Time (Seconds) 0 5 10 15
Concentration (Molar
0.0 0.0 0.0 0.0 0.0
1.0 0.0 4.0 8.0 11.0
1.5 0.0 10.0 20.0 26.0
2.0 0.0 15.0 21.0 21.0
2.5 0.0 25.0 26.0 26.0
Processed results
Gas evolved in test 1 (cm3) Gas evolved in test 2 (cm3) Average gas evolved (cm3) Initial rate of reaction (cm3/s)
Concentration (Molar)
0.0 0.0 0.0 0.0 0.0
1.0 4.0 4.0 4.0 0.8
1.5 10.0 10.0 10.0 2.0
2.0 18.5 15.0 16.7 3.3
2.5 29.0 25.0 27.0 5.4
My processed results contain the results for the amount of gas that had evolved in 5 seconds for both tests then the mean average for both of them and then I calculated the initial rate of reaction.
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.
Concentration (Molar) Test 1 Test 2
1.0 4.0 4.0
1.5 10.0 10.0
2.0 18.5 15.0
As you can see from this table as the concentration doubles then the rate of reaction approximately quadruples. My graph also shows that as the concentration doubles then the initial rate of reaction approximately quadruples.
When the concentration is 1M the rate = 4 = 0.8 cm3/second
5
When the concentration is 2M the rate = 16.7 = 3.3 cm3/second
5
I therefore conclude that:
1. The initial rate of reaction increase as the concentration of the acid increases
2. There is a fourfold increase in the rate of reaction as the concentration increases
3. As the concentration doubles the initial rate of reaction is approximately squared
My original prediction was that the initial rate of reaction would double as the concentration doubles. This was incorrect because it was not based on experimental evidence.
Evaluation
Was I precise in my measurements?
I feel that I was precise and accurate in recording measurements.
I measured the acid accurately by measuring the acid when the bottom of the liquid meniscus just touched the line on the measuring cylinder.
Liquid Meniscus
Measuring cylinder
I accurately cut the magnesium ribbon to the nearest millimetre with the ruler provided.
I measured the starting and the end temperature accurately with a thermometer to the nearest .5OC.
I accurately measured the volume of gas evolved to the nearest .5cm3.
I accurately measure the time that had elapsed to the nearest second with the stop clock.
Did I take enough readings?
Not enough concentrations were used for a good graph. I should have used concentration 3M acid ought to have been done but it was not known then that it was necessary and required.
The results that I did collect were reliable as I repeated the experiments twice to obtain good average results. My results were not only reliable they were reproducible.
Anomalous results
I obtained two anomalous results.
For concentration 2M there was 18.5cm3 of gas produced in test one, and in test two there was 15.0cm3, which is a 3.5cm3 difference:
= 23% error
For concentration 2.5M acid there was 29.0cm3 gas produced in test one, in test two the was 25cm3 gas produced, which id a difference of 4cm3:
= 16% error
These errors both occurred in the first run, when the technique and practical skill had not been perfected over a large number of experiments. The more times an experiment is preformed then the more accuracy and skill the student acquires. At higher concentrations there is more heat evolved which gives a larger volume error, since gases have a larger volume at higher temperature.
Another reason for these anomalous results is that the plunger on the syringe may have been sticking on the barrel after a lot of runs, which would have given me lower readings.
Improvements to my procedure
Improvements to my experiment are that I could stop the syringe plunger sticking by applying a thin coating of Vaseline to it.
I could also use a monometer to be sure that the atmospheric pressure inside the syringe is the same as the pressure outside of the syringe.
Monometer Gas Syringe
To be sure that the pressure is the same inside the syringe as outside the syringe the water levels in the monometer must be level.
The last improvement to my procedure is that I should check for gas leakages where the bung is placed into the conical flask, a smear of Vaseline would help me do this.
Further work
There are several things that I could do for further work. The first is to find out what the initial rate of reaction would be for concentrations 1.25M hydrochloric acid and 1.75M hydrochloric acid as it would be interesting to see how the rate increases compared to 1M hydrochloric acid.
Another experiment that I could do is change the type of acid that I use.
I could use sulphuric acid. This is a dibasic acid and its molecular build-up is H2SO4 and hydrochloric acid is 2HCL, because of this I would obtain different results. I could also use phosphoric acid, which is a tribasic acid, and its molecular build-up is H3PO4, I would also obtain different results if I used this type of acid. Nitric acid is a monobasic acid but its molecular build-up is HNO3, which is very similar to the molecular build-up of hydrochloric acid so the results that I would obtain from using this acid would be similar to the ones I already have, so I would not use this for any further experiments. The reason I could use a different type of acid for any further work is to find if the is a difference between them if their molecular build up is different.
I could also use the less reactive metals of the reactivity series (zinc, aluminium, iron and lead) that way I could find the initial rate of reaction at 5 seconds for the higher concentrations of acid like 3.0M or 3.5M and I could find there relative activity.
Bibliography
I obtained most of the information that I needed for my experiment form my teacher and exercise book. I also obtained information from several science textbooks and computer encyclopaedias. I obtained a small amount of information from the Internet.