reaction rate
...clusion I could have also decided to change whether or not to use a catalyst with the experiment but I decided not to as we wouldn’t be able to get a wide range of results as in certain amounts the catalyst would make the reaction to fast to time. Prediction I predict that the higher the concentration of acid used in the experiment the faster the reaction rate will be so therefore the magnesium will react with the hydrochloric acid faster to produce 40cm cubed of Hydrogen. I also predict that the time taken for the magnesium to react with the hydrochloric acid to produce 40cm cubed of Hydrogen will not increase in direct proportion to the molarity of the acid and will slow down with time. Hypothesis In order for the hydrochloric acid and magnesium particles to react together they must collide with each other and the collision must have enough energy. The particles in a liquid move around continuously when an acid particle collides with a magnesium particle it must have a set amount of energy called the activation energy for the reaction to take place if the collision does not have enough energy no reaction takes place. In a successful collision bonds are broken using the activation energy and new bonds are formed. The reaction rate depends on how many successful collisions there are in a given period of time. As the concentration of the acid increases the number of successful collisions take place and therefore the reaction rate increases this is because in a less dilute acid there are less acid particles so there is less chance of a magnesium atom hitting a acid particle but in a more concentrated acid there are more acid particles so the chances of collision increase. Magnesium + Hydrochloric Acid = Magnesium Chloride + Hydrogen Mg (s) + 2Hcl (aq) = MgCl2 (aq) + H2 (g) (Adapted from Complete Chemistry page 126-127) The rate of the reaction will not increase in direct proportion to the concentration of acid as the nearer the reaction rate gets to its optimum level the more the graph will flatten out as the difference between reaction rates decreases The preliminary work I did also seems to back up my prediction as they seem to show that the more concentrated the acid is the faster the reaction will be although these results are not reliable as the range of results is not wide enough and also the results were not collected with as much care as the results for this investigation. Method We poured the 25ml of 1M Hydrochloric Acid from the measuring cylinder into a conical flask we set the gas syringe to 0 cm cubed then dropped the 5cm strip of Magnesium into the Hydrochloric Acid then put the bung into the Conical flask we then timed how long it took for 40cm cubed of hydrogen to enter the Gas syringe we took the results then repeated the experiment for each of the concentrations of acid that we decided to use. We decided to use 5cm strips as opposed to 4cm strips as it would provide a wider range of results while still being easy to cut and get into the acid completely. Diagram Results A table to show the time taken for a 5cm strip of Magnesium to react with 25ml of varying strength Hydrochloric acid to produce 40cm cubed of Hydrogen Concentration of 25ml of Hydrochloric Acid (Mol) Time taken for 40cm cubed of Hydrogen to be produced Test 1 (s) Time taken for 40cm cubed of Hydrogen to be produced Test 2 (s) Average time taken for 40cm cubed of Hydrogen to be produced (s) 1 39.03 41.29 40.16 1.125 31.39 31.20 31.295 1.25 24.02 23.73 23.875 1.375 18.30 20.01 19.155 1.5 16.82 17.93 17.375 1.625 16.36 15.32 15.84 1.75 13.23 13.28 13.255 1.875 11.18 12.07 11.625 2 9.30 10.86 10.08 Conclusion I have drawn 3 graphs one for each time that I performed my experiment and one for the average. My graphs show that my prediction was correct the reaction rate increased as the concentration of the acid increased also the reaction rate slowed down as the reaction rate began to approach its optimum level. Although the increase in the reaction rate did slow down as the reaction rate reached its optimum level it did not slow down as much as I anticipated in my predicted graph. My graph shows a basic curve with one anomaly that distorts the curve this is because we collected an odd result on test one and this distorted the average, There is negative correlation and the graph starts off steep but becomes less so as the rate of reaction nears its optimum level. On average for every 0.125 molar increase in the Hydrochloric acids strength the time taken for 40 cm cubed of hydrogen to be produced is reduced by 3.34 seconds although this could not be used scientifically as the graph shows that the increase in the rate of reaction starts to slow down. I feel my Data is quite precise as it backs up my prediction and my hypothesis which is “In order for the hydrochloric acid and magnesium particles to react together they must collide with each other and the collision must have enough energy. The particles in a liquid move around continuously when an acid particle collides with a magnesium particle it must have a set amount of energy called the activation energy for the reaction to take place if the collision does not have enough energy no reaction takes place. In a successful collision bonds are broken using the activation energy and new bonds are formed. The reaction rate depends on how many successful collisions there are in a given period of time. As the concentration of the acid increases the number of successful collisions take place and therefore the reaction rate increases this is because in a less dilute acid there are less acid particles so there is less chance of a magnesium atom hitting a acid particle but in a more concentrated acid there are more acid particles so the chances of collision increase” but has few odd results. My graph was curved and to work out the equation of the line I will calculate the gradients of 3 parts of the graph Position on graph Gradient A-B Y/X = 42/20Gradient isY= 2.1x2.1ml³ /s B-C Y/X = 16/20Gradient is Y= 0.8x0.8 ml³ /s C-D Y/X = 11/20 Gradient isY= 0.55x0.55 ml³ /s This Table shows that the rate of reaction is not directly proportional to the molarity of the acid as the gradient of the line changes from point to point. .At the top of the graph where the concentration is at its highest the gradient is at its steepest. The gradient falls as you go from left to right across the graph and the table of results. This can be explained because the reaction between magnesium and hydrochloric acid exothermic. This means that in the reaction heat is produced. When the concentration of acid is higher, more heat is produced, this means that the hydrochloric acid particles would have more energy and therefore move quicker so when they collided with the magnesium there was more chance of the collision being successful. The solutions with a lower concentration will produce less heat when a reaction takes place and therefore the particles will not have as much energy and therefore speed, compared to ones with a higher concentration. So there is less chance of a successful collision. Therefore this explains the curve . This experiment seems to prove my hypothesis correct though this was expected as I obtained much of the ideas from a science textbook for this reason there is nothing I can add to my hypothesis. The results we got in this investigation look quite similar to the results I got in my preliminary work but on the scale we are working on the differences between our final results and our preliminary results are quite noticeable. Evaluation My experiment was adequately suitable for collecting evidence to allow me to access the accuracy of my prediction but it also had some anomalous results such as Graph 1 concentration 1.375 Molars which does not fit in with the rest of the results as the time taken for 40 cm cubed of hydrogen to be produce dropped down too far from the previous result (1.25 Molars). There were many reasons that may have contributed to the odd results in this experiment such as the inaccuracy of our equipment that resulted in our odd result. If we had had more accurate equipment t...