Investigating What Effect Concentration Has on the Rate of Reaction

Investigating What Effect Concentration Has on the Rate of Reaction
The theory that we use to explain how different variables change the rate of reaction is called the collision theory. It is when two or more particles collide together with enough energy to cause a reaction. For a reaction to take place, the particles of the substances that are reacting have to collide. If they collide, with enough energy then they will react. The minimum amount of kinetic (movement) energy that two particles need if they are going to react when they collide is called the activation energy. There are therefore two main ways of increasing the rate of a reaction: 1) Increase the number of collisions or increase the number of particles 2) Increase the amount of movement (kinetic) energy so that more collisions lead to a reaction. [image] aim: The aim of my experiment is to investigate, what effect concentration has on the rate of reaction. I am going to put Mg strip into different concentrations of hcl and find out how long it takes for each one to disappear, and from this determine the rate of reaction. The rate of a chemical reaction is a measure of how fast the reaction takes place. It is important to remember that a rapid reaction is completed in a short period of time. Some reactions are very fast, e.g. (the formation of silver chloride precipitate when silver nitrate and hydrochloric acid solutions are mixed. In this investigation I will test different concentrations of acid reacting with magnesium. hypothesis: I predict that the higher the concentration the higher the rate of reaction. The reason for my prediction is because in a higher acid concentration there are going to be more particles of acid, for the Mg strip to collide with. I predict that as the concentration of the hydrochloric acid increases, the time taken for the magnesium to disappear decreases. I predict that when the concentration of the hydrochloric acid doubles, the rate of the reaction doubles.
linking prediction TO collision theory: The collision theory describes how the rate of reaction increase (the time taken for the magnesium ribbon to disappear when it is reacted with hydrochloric acid) when the concentration of hcl increases. The theory states that if; the more concentrated the reactants, the greater the number of collisions between particles increases. This also explains why the greatest rate of reaction is usually as soon as the reactants have been mixed, i.e. they are both at their highest concentrations. As the reaction continues, the concentration of the reacting substances decreases and so does the rate of reaction. We must consider what happens when a reaction takes place. First of all the particles of the reacting substances must collide with each other, and secondly a fixed amount of energy called activation energy (Ea) must be reached if the reaction is to take place. If the particles can produce the right amount of energy (i.e. if they collide fast enough and in the right direction) a reaction will take place. The reaction is speeded up if the number of collisions is increased. In this investigation we must consider the topic of variables. Clearly, the time taken for the magnesium to disappear when it is placed in different concentrations of hcl is related in some way. The higher the concentration of hcl you use, the less time it takes for the magnesium to disappear and so the rate reaction increases. preliminary work apparatus In my preliminary work I used the following apparatus: - Goggles - Beaker - Measuring cylinder - Stopwatches - Scissors products In my preliminary work I used the following products: - Distilled water - HCl - Mg strips & powder safety: To make sure that my investigation was safe, I wore goggles when conducting the experiment. I also handled the hcl with care, and disposed it of safely when finished. I carried out my preliminary experiment just to see if the apparatus I used was safe, and to obtain a method which will give me accurate results. method I used the following method for my preliminary experiment: ? I used the scissors to cut down the five Mg strips ? each magnesium strip was 5 cm in length ? I made five different mixtures of dilute HCl (with the concentration of 2 moles per dm3) and distilled water. The solutions I made are as follow; 50 cm3 of HCl 40 cm3 of HCl & 10 cm3 of H2O 30 cm3 of HCl & 20 cm3 of H2O 20 cm3 of HCl & 30 cm3 of H2O 10 cm3 of HCl & 40 cm3 of H2O ? I dropped a Mg strip into each one of the solutions ? one by one ? and timed it ? I stopped timing when the Mg strip had disappeared When I was examining my experiment, I found out that some of the Mg strips took longer than the other to react, the reason for this was because, there was an oxide layer on the Mg strips and on some it was thicker than the other. That is why I decided that I will sand the Mg strips down before putting it in my solutions. Also that 5cm in length was too long for it to react with 10 cm3 of HCl & 40 cm3 of H2O and this made it difficult for me to time it, due to the length of lesson. I did another preliminary experiment, this time by using Mg powder and not a strip, but the experiment was very quick and it was hard to time it accurately. The reason for this was because the powder provided acid with more surface area to react with. So then I decided that I will use the Mg strip for my real experiment. apparatus (that I decided on after the preliminary experiment): - Goggles - Beaker - Measuring cylinder - Stopwatches - Scissors - Sand paper products (that I decided on after the preliminary experiment): - Distilled water - HCl - Mg strips fair test: I will make my experiment a fair test by keeping the volume of each concentration the same. I will keep the starting temperature of each concentration the same, the length of each magnesium strip the same, the surface area of each magnesium strip the same however; I will sand the Mg to remove the oxide layer on the magnesium ribbon. I will sand the strips down the same amount each time on both sides. The reason for this is because I have to find out the effect that the acid concentration has on rate of reaction with the Mg. Therefore the only variable I will change is the concentration because the results I obtain can only be due to the change in concentration and therefore allow me to analyse and see if increasing the concentration does in fact increase the rate of reaction. I am only going to change the independent variable, in order to get accurate dependant variable. The only things that I am going to change are the control variables. method 1. I will cut 15 Mg strips each 3 cm long 2. Then I will sand the oxide layer off the Mg strips, I will rub the sand paper only three times on each one to make it fair. 3. Then I will make five different mixtures of dilute HCl (with the concentration of 2 moles per dm3) and distilled water. My mixtures are going to be the following: 50 cm3 of HCl 40 cm3 of HCl & 10 cm3 of H2O 30 cm3 of HCl & 20 cm3 of H2O 20 cm3 of HCl & 30 cm3 of H2O 10 cm3 of HCl & 40 cm3 of H2O 4. After making each solution, I will drop in a strip of Mg and time it. 5. I will stop timing when the Mg strip has disappeared ? this is where the reaction stops 6. Then I will repeat the experiment 3 times in order to get accurate results from these experiments, so that I can calculate the average and then analyse. result table time taken for the magnesium ribbon TO dissolve IN seconds (s) correct TO 2 decimal places experiment NO: concentration IN moles per DM3 1 2 3 average time for MG TO dissolve (s) correct TO 2 decimal places rate OF reaction (1/time taken) (s) correct to 4 significant figures 0.4 599:23 617:20 623:09 617:17 0.001620 0.8 223:90 229:73 225:40 226.34 0.004418 1.2 58:29 64:79 63:09 62:06 0.01611 1.6 21:68 27:53 23:27 24:16 0.04139 2 12:31 15:17 13:08 13:52 0.07396 analysis: The results of my graph supports my prediction that as the concentration increases the rate of reaction also increases. The higher the concentration the quicker the Mg strip disappears. The first graph that compares the rate of reaction with the concentration is meant to be a straight line, but it is a curvy shape, the graph has its largest gradient or it is steepest at higher concentration. It varies from the acid concentration higher than 1.2 molar. The only possible explanation to this is at higher concentration, above 1.2 molar, the rate of reaction is very fast because it is an experiment that gives off heat reaction and an increase in temperature will also increase the rate of reaction. To prove this concept some experiments must be carried out at acid concentrations higher than 2 molar. The reason why the Mg strip disappeared quickly in the high concentrated acid was because there were more of the acid particles for the magnesium particles to collide with. Where as in the solution with 40 cm3 distilled water and 10 cm3 hcl, there were less of acid particles for magnesium particles to collide with, which is why it took longer for Mg strip to dissolve in the less concentrated acid. evaluation: I think that the investigation I carried out on rate of reaction was quite successful. I believe that we gained quite accurate and sufficient results, shown on our graph and tables that concludes the experiment, and to back up my hypothesis. My final results were quite reliable, due to the precautions I took to make this a fair test. I think that the method I used was also quite good and reliable. In this experiment I had difficulty with accuracy timing, due to the fact that the stopwatch did not as soon as the magnesium strip disappeared, therefore my results weren?t accurate. Although my results were quite reliable, but I could have obtained better results by using a wider range of acid concentrations. The first set of experiment that I did was a lot quicker than the other two sets, it was anomalous. Still the reasons why I kept that set and not do it again is because it was the whole set, and not just one, that was anomalous. The only possible explanation to this is that the hcl I used for the first set of experiments might be a bit stronger than the other one. I did the experiment three times to get a precise and accurate average. The first set of results that I took was lower than the other two sets, which maybe because the acid was a bit stronger than the other two sets. So my average was affected because of the first set, which meant that my rate of reaction was higher than my colleagues in school. However, it did not affect my results so much because I carried out the experiment three times. Looking at the overall experiment I have thought of a number of improvements to give me more and better accurate results. Firstly the concentrations were measured using a measuring cylinder and could be made more accurate using titration. Also when sanding the Mg strips, you can never be accurate, I could get pre-sanded Mg ribbons. Another thing that I could have done to obtain better results is that I could have used the same hydrochloric acid so that it is of the same molarity. Using more types of molar hydrochloric acid solutions would have helped me obtain better results, and more accurate results; so that I can make sure the results are totally correct. If I was to do this again, I would use the concentration of 0.2 molar per dm3, 0.6 molar per dm3, 1.0 molar per dm3, 1.4 molar per dm3 and 1.8 molar per dm3, as well as the other solutions that I used before; this would help me obtain better results. I think that this experiment was not very reliable due to the fact that I had some anomalous results, especially the first set of results. Still I think it is quite a firm conclusion because I carried out the experiment three times, which gave me a much better average of my results. To get more relevant results I would use more concentrations of hcl ? as explained above. Overall, given the apparatus that I got to carry out the test, I think this experiment turned out to be very successful, and I?m quite please with my results.

Investigating What Effect Concentration Has on the Rate of Reaction 9.2 of 10 on the basis of 1921 Review.