If I double the concentration of the acid from 1mole to 2moles of 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 2moles of hydrochloric acid than in 1mole, 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 speed of reaction.
As we increase the concentration, the rate of reaction increases. There are more particles in the same volume of water and so there will be a greater chance of a collision. Therefore there is a greater chance of acid particles colliding and reacting with particles on the surface of the marble. Not all collisions between particles result in reactions, if they were then all reactions would be practically instantaneous, but the more collisions, the higher the chance that some will be effective.
Factors
I also believe that there are certain factors which may affect the rate of the reaction, it may either increase or decrease. The factors which may affect the rate of reaction 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 so there would be meaning collisions per second this will then lead to 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 as the temperature increases. This means the acid particles move with more energy so they will collide with the magnesium with additional energy, which will give more successful collisions per second.
· Surface area of the magnesium
If the magnesium had a bigger surface area 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 then there are 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.
Ways in which I will record my experiment
There is several ways which I could record my experiment, but here are the two which I am planning to do:
Amount of gas evolved
I could use a gas syringe to collect the gas that will evolve from my experiment. These results could then be used to calculate the initial rate of reaction.
How long the magnesium takes to react
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 – This will be worked out when I find how long the magnesium takes to react.
Initial rate of reaction – This will be worked out when I find the amount of gas evolved.
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
· 0.5M hydrochloric acid
· 1M hydrochloric acid
· 1.5M hydrochloric acid
· 2M hydrochloric acid
· 2.5M hydrochloric acid
· Distilled water
Apparatus
· Measuring cylinder
· Conical flask
· Safety glasses
· Test tubes
· Test tube rack
· Gas syringe
· Ruler
Safety
I will need to make my experiment as safe as possible for myself and other students and they 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 cause damage
· Safe disposal of reagents and laboratory chemicals
· Care when returning all used glassware and equipment at the end of the experiment
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 timing how long a magnesium strip will react with different concentrations of hydrochloric acid. I only require three results as I am going to measure the average speed of reaction for each concentration of hydrochloric acid.
I am also 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 delivery tube and a rubber bung to the conical flask that the reaction will take place.
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 they will then be reacted. 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 water in the hydrochloric acid is not giving off any hydrogen gas, 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 3cm³ of hydrochloric acid with 1.5 cm of magnesium ribbon then I could obtain some good results for the first experiment, but in the second experiment I will require to increase the volume of hydrochloric acid to 10cm³.
I also used these quantities of chemicals because it has kept the temperature increase to a minimum.
Method
1st Experiment
1. Put on safety goggles
2. Collect all the equipment required to do the experiment and set them up, which includes magnesium, 5 different concentrations of hydrochloric acid, 5 test tubes, test tube rack, measuring cylinder and stop clock
3. Measure out 3cm³ of 0.5M hydrochloric acid using the measuring cylinder
4. Pour the hydrochloric acid into the test tube
5. Measure 1.5cm of magnesium ribbon.
6. Drop the magnesium into the test tube
7. Start the stopwatch
8. Stop the stopwatch once the magnesium has fully reacted and record the time.
9. Repeat steps 1-8 twice, but with 1, 1.5, 2, 2.5 moles of Hydrochloric Acid to obtain good results
.2nd Experiment
1. Collect all the equipment required to do the experiment and set them up, which includes magnesium, 5 different concentrations of hydrochloric acid, conical flask, gas syringe, delivery tube, clamp, measuring cylinder and a bung
2. Put on Safety goggles
3. Measure out 10ml³ of hydrochloric acid with 0.5 moles
4. Measure 1.5cm of magnesium ribbon.
5. Pour the hydrochloric acid into the conical flask
6. Drop the magnesium into the conical flask
7. Quickly use the bung to seal the hole in the conical flask
8. Start timing with the stop clock
9. After one minute stop the stopwatch and record the amount of gas produced.
10. Repeat steps 1-9 twice, but with 1, 1.5, 2, 2.5 moles of Hydrochloric Acid to obtain good results.
Obtaining
Results for 1st experiment
With this set of results I am planning to work out the average for each concentration of hydrochloric acid to plot a good graph. To work out the average I must firstly add up the three different times together.
Once this has been done I will need to divide each total time by three as there are three sets of data, this should then give me the average.
Results for 2nd Experiment
With this set of results I am planning to work out the average for each concentration of hydrochloric acid to plot a good graph.
To work out the average I must firstly add up the three different times
Once this has been done I will need to divide each total time by three as there are three sets of data, this should then give me the average.
The results were fairly accurate as they portray some good sets of data, from which I plotted two good graphs one for each experiment
Conclusion
My results table and graph show me that when I increase the concentration of the hydrochloric acid, rate of reaction also increases.
Altogether I tested 5 different concentrations of hydrochloric acid. 0.5M, which was the lowest concentration of acid that I used, there was only a tiny amount of gas evolved, but the time taken for the magnesium to completely react was over 700 seconds. 2.5M hydrochloric acid, which was the highest concentration that I used, produced the fasted rate of reaction. I repeated both experiments three times to work out a good average and 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 because if the concentration is doubled then there are twice the many acid particles, which does not necessarily mean that there has will be twice the amount of collisions per second as the reactions depend on the energy of the collision.
I therefore conclude that:
1. The 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 rate of reaction does not double
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
If I were to do the experiments again I would clean the all the magnesium ribbons before carrying out the experiment and measure the temperature before and after, I could also weight the conical flask before and after to see if there is any change. I would also try and use the same volume of Hydrochloric Acid in both experiments so then I can compare the two sets of data.
Was I precise in my measurements?
I feel that I was precise and accurate in recording measurements.
I measured the acid accurately by making sure it was level with the line to which I had to measure it on the measuring cylinder.
I made sure that the magnesium ribbon were all the same size by measuring it with a rules, and they all read 1.5cm.
I accurately measured the volume of gas evolved to the nearest .1cm³.
I accurately measured 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 very 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 three times to obtain good average results. My results were not only reliable they were reproducible.
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 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. Marx
I could use sulphuric acid. This is a dibasic acid and its molecular build-up is H2 SO4 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 H 3PO4, 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.
