The smaller the pieces the larger the over all surface area, this will result in an increased number of collisions, and an increased reaction time.
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After having looked at all the possible options of what I could look at, I have decided to find out how the concentration of Hydrochloric acid effects the rate of reaction.
Prediction.
I predict that the higher the concentration of the acid, the faster the rate of reaction will be. I predict this because I know that the higher the concentration of the acid, the greater the number of acid ions present in that volume. This means that there are more acid ions colliding with the particles on the surface of the reactant (magnesium) thus increasing the rate of reaction.
An increase in concentration will lead to an increase in particles and a greater chance of successful collisions and this will mean that there will be a greater number of resulting successful collisions. Energy from these collisions is needed to break chemical bonds.
Equations for reactions
Metal + acid salt + hydrogen
Mg + 2HCl (r) MgCl2 + H2
Magnesium + Hydrochloric acid (r) Magnesium Chloride + Hydrogen
Equipment.
5 different concentrations of Hcl (0.5,1.0,1.5,2.5& 3.0 Molar)
1 gas syringe
1 conical flask (or dividing flask if possible)
1 stop watch
Sand paper
Goggles
1 measuring cylinder
1 top pan balance
Magnesium ribbon
Variables
The only variable is the different concentrations of Hydrochloric acid.
Plan.
☺ Collect all the equipment needed ( see equipment list ), always remember to follow safety rules ( tie back long hair, wear safety goggles and put chairs and bags under desks.)
☺ Set up experiment as shown bellow
☺ Weigh out and polish using sandpaper in order to get rid of any impurities, the amount of magnesium that you decided to use after looking at the results of your preliminary work.
☺Put a given volume of the first conentration of acid you want to test into a measuring cylinder, to avoid spills do this using a funnel and always wear safety goggles.
☺ Put this acid into the chronicle flask (or if possible divided flask).( make sure that the volume of acid you have chosen stays consistant throughout your experiments.)
☺ Add the magnesium ribbon to the acid AND at the same time put the bung securely into the chronicle flask( dividing flask) and start the stop clock.
☺ When the reactants meet hydrogen gas will be seen bubbling off and will rise pushing the syringe out, you can now take recordings every five seconds.
☺ take this measurment every five seconds untill there is no evidence of any further reaction taking place inside the chronicle flask.(divided flask)
☺ always remember to take the measurements from the same line on the syringe and as far as possible allow the same person to carry out this job to ensur maximum accuracy. Take three consecutive readings at the end to ensure complition.
Always measure from the
Same line i.e. this one
☺Five or more different concentrations of hydrochloric acid should be used and each concentration should be tested at least three times to give sufficient data from which an average can be found.
☺ When I have found sufficient results I will plot graphs with lines or curves of best fit. I will identify any anomalous results, and repeat the part of the experiment for which it was found. If it still proves to be anomalous I will try to identify why.
☺ I will do the same for each step of the experiment, making them all fair tests by:-
➔ Keeping the mass of magnesium consistent.
➔Keeping the volume of Hydrochloric acid consistent.
➔Make sure I take the results as close to the five-second mark as possible.
➔ Start the stop clock as soon as possible after the two reactants have mixed.
➔ I will do all the experiments on the same day so my results are not varied by different humidity conditions ect.
➔ I will polish the magnesium before using it to make sure that I got rid of any impurities.
Preliminary Work.
We did some preliminary work in order to find out a suitable mass of magnesium to use and suitable concentrations of hydrochloric acid. To begin to work this out I am going to look at the different masses of magnesium I could use.
For my preliminary work I used 0.06grammes of Magnesium ribbon, 50ml of hydrochloric acid
0.06 g of Magnesium ribbon, 50ml of hydrochloric acid. Acid used 3 molar. Time intervals every 15.0 seconds.
0.06 g of Magnesium ribbon, 50ml of hydrochloric acid. Acid used 3 molar. Time intervals every 5.0 seconds.
0.06 g of Magnesium ribbon, 40ml of hydrochloric acid. Acid used 3 molar. Time intervals every 5.0 seconds.
0.06 g of Magnesium ribbon, 30ml of hydrochloric acid. Acid used 3 molar. Time intervals every 5.0 seconds.
0.05 g of Magnesium ribbon, 30ml of hydrochloric acid. Acid used 3 molar. Time intervals every 5.0 seconds.
Throughout the previous preliminary work I carried out, I used different amounts of Hydrochloric acid and I added Magnesium to it. I used different volumes of acid so I could compare the results to find out which volumes and weights gave the most satisfactory results. As a group we decide to use 30ml of acid and change the concentration of the hydrochloric acid used.
All of the concentrations used in the preliminary work produced similar results so I decided instead to test concentrations a little further apart, for the main experiment.
0.5 1.0 1.5 2.5 3.0
Increasing concentration.
If I use a wider variety of concentrations I think that my results will be more varied. From these results I could obtain reliable results, from which graphs could be plotted.
As a group we decided to use 0.05g of magnesium and 30ml of hydrochloric acid and the concentrations we will use are 0.5 molar, 1.0molar 1.5molar,2.5molar and 3 molar.
In my equipment list and also in my plan I wrote that I would use a divided flask if possible, because I knew that this would ensure that our results were as accurate as possible. However this wasn’t possible because I couldn’t get a divided flask. So instead I will use a chronicle flask although this may make the results a little in accurate because we will have to add the magnesium to the acid and then quickly place the bung in to avoid any loss of hydrogen. This may prove difficult especially when using the higher concentrations of acid because large reactions will occur in a shorter amount of time.
RESULTS
0.05g Magnesium ribbon 0.5molar hydrochloric acid 30ml of acid.
If my prediction is right this will be the slowest reaction with the most results.
0.05g of magnesium ribbon. 1.0 molar hydrochloric acid of which I will use 30ml.
In the table above there are some results that are obviously anomalous, this can’t be seen very quickly but on the eighth result (40.00) we notice that the result for the third group is lower than the other two which could possibly be normal but this figure continues to stay the same over the next five results. The final time that we took the reading the third result was in total 26 cm squared behind the second result which we found very unlikely especially as the result had been consistent for so long before hand.
Because of these results as a group we decided to re-test the 1.0 molar acid. To make the test fair we managed to fit the re-test in on the same day as the other experiments, ensuring that the results we as accurate as possible.
0.05g of magnesium ribbon. 1.0 molar hydrochloric acid of which I will use 30ml.
RE-TEST
The above results are what I would have expected before doing the experiment and shown no signs of anomalous results.
Amount of hydrogen produced (cm cubed)
Amount of hydrogen produced (cm cubed)
0.05g of magnesium ribbon. 1.5 molar hydrochloric acid of which I will use 30ml.
0.05g of magnesium ribbon. 2.5 molar hydrochloric acid of which I will use 30ml
Amount of hydrogen produced (cm cubed)
0.05g of magnesium ribbon 3 molar hydrochloric acid of which I will use 30ml
Amount of hydrogen produced (cm cubed)
Conclusion
By analysing the graphs I have drawn from my results , I can see that the curves of best fit get steeper as the Hydrochloric acid gets more concentrated. E.g.
Increasing Gradient for line of best fit.
0.5 1.0 1.5 2.5 3.0
Increasing concentration.
This there fore proves that my initial prediction was correct, I said that as the concentration of the acid increased so would the amount of hydrogen produced by the reaction. I also said that the amount of hydrogen produced would increase because the reaction would be faster because of the increased number of acid particles, this meant that there were more reactant acid molecules passing between the water molecules making the needed collisions more likely. The Gradient of the graphs increase with the concentration of the acid because as the rate of reaction increases more hydrogen is produced.
To make sure that the gas given off was hydrogen, I did a lab test, and by placing a lit spill inside a test tube that we thought contained hydrogen, we could tell the gas was hydrogen because it gave off a squeaky “pop”.
WORD EQUATION.
Magnesium + Hydrochloric acid ➔ Magnesium chloride HYDROGEN
SYMBOL EQUATION
Mg + 2HCl ➔MgCl2 +H2
Evaluation
By drawing the curves of best fit on all the graphs I have drawn I can see that on the first time I tested the 1 molar acid the experiment could not have been 100% accurate because there were some anomalous results, the whole of the third set of results were anomalous and this could have happened for one or two of many reasons. The Final value for each concentration should have been the same because I never deliberately changed the amount of magnesium or acid, so the eventual amount of hydrogen should have been the same for all the experiments. By looking at the graph however I can immediately see that this didn’t actually happen because the end amounts of hydrogen are al different.
All of these inaccuracies must have had some cause.
➔ Some of the hydrogen may have escaped from the chronicle flask before the bung was put in this would be more likely for the more concentrated acids because the reaction would be faster and produce more hydrogen quickly.
➔Inaccurate timing. I don’t really think that this would have been a factor that would effect the accuracy but possibly added together the points of seconds could become enough for a results to look out of place.
➔The gas syringe may have been sticking at times although as a group we did repeatedly clean the syringe, to avoid this. But if this was happening the results would have been very much so altered.
Different conditions may have effected the results e.g. humidity of temperature. To limit this as much as possible we did all of our experiments on the same day.
➔The reaction may not quite have finished , little bits of magnesium may not have reacted and the experiment may have been prematurely ended.
➔ The bung may not have been fitted correctly and therefore in some experiments push into the flask further than in others.
➔Impurites may have started to form on the cleaned Magnesium because it was left out for different lengths of time for each experiment.
➔ the Magnesium ribbon may have been thouroughly cleaned for one evxperiment and not for anpother therefor slowing down the rate of reaction.
➔ the top pan balance may not have been entirley accurate because in one of our lessons it wasn’t workoing properly and it ws posible that one of our pieces was weighed on the faulty balance.
∙The loss of gas could have been prevented by the use of a dividing flask instead of a chrolicale flask.Because with a dividing flask youcantip the reactants together with the bung already firmly in place. This would mean that there would be a redced loss of gas.
∙ To Ensure the most accurate timeing possible I could get 2 or 3 pepole to use a stop clock and then take an average of each persons time.
∙ We did polish the gas syringe quite offten butbif it were to be cleaned after each experiment there would be even less chance of it sticking.
∙ The same balance should always have been used to weigh out the magnesium to avoid and major descrepancies.
∙ The magnesium should always have been used as quickly as possible after cleaning to get best results.
∙The chronical flask should always be closly obsered to make ure the eraction was totally finished before stoppng the experiment.
To get the same amount of hydrogen for each of the experiments I did I could:-
➔Use a more accurate top pan balance.
➔ make sur nobody leans on the desk whilst weighing.
➔be totally accurate when measuring the volume of acid to use.
My annomoleus results may have been due to the acctual concentration in the botle beiong different to what the labble said, however I think that my annomolus results had more to do with hydrogen escaing because the reaction happenened at the same rate as the others at the same concentration but the third test finished a lot sooner than the other experiments.