The Effect of Concentration of Acid on the Rate of Reaction With Calcium Carbonate

The Effect of Concentration of Acid on the Rate of Reaction With Calcium Carbonate
Calcium + Hydrochloric ð Calcium + Carbon + Water Carbonate Acid Chloride Dioxide CaCO3 (s) + 2HCl (aq) ð CaCl2 (aq) + CO2 (g) + H2O (l) Introduction I will be using the reaction between calcium carbonate and hydrochloric acid to see how the concentration of acid affects the rate of a reaction. By doing the above experiment I will prove that the higher the concentration of acid, the faster a reaction will occur. I have carried out a previous experiment called the ?Disappearing Cross?, in which I used the reaction between thiosulphate, hydrochloric acid and water to see how concentration affects the rate of reaction. When we added the hydrochloric acid to the water and thiosulphate a reaction occurred, causing the water to become foggy so that the cross was no longer visible through the conical flask. The results for the Disappearing Cross experiment were as follows; Volume of Thiosulphate (Cm3) Volume of Water (Cm3) Volume of HCl (Cm3) Concentration (%) Time taken for X to disappear (seconds) 5 25 5 17 711 10 20 5 33 286 15 15 5 50 185 20 10 5 67 113 25 5 5 83 82 You can see that when the hydrochloric acid was most dilute the cross took 711 seconds to disappear, and when the acid was most concentrated the cross took just 82 seconds to disappear. This shows that the more dilute the concentration of acid, the slower the rate of reaction and the more concentrated the acid the faster the rate of reaction because when acid is more concentrated there are more molecules, therefore increasing the chance of a successful collision, and speeding up the reaction. This is known as the ?Collision Theory?. I am now going to do another experiment, using calcium carbonate and hydrochloric acid to see if the same effect is observed with a different reaction. Apparatus Needed o Gas syringe o Retort stand o Conical flask o Boss and clamp o Bung o 2x Measuring cylinder o Stopwatch o Delivery tube o Beaker o Balance o Goggles o CaCO3 (Medium sized Calcium Carbonate chips) o H2O (Water) o HCl (Hydrochloric acid) Diagram Below is a diagram showing how apparatus should be set up: [image] Method o Set apparatus up as shown in the diagram above o Using the balance, measure 5g of Calcium Carbonate o Measure 30cm3 of acid solution o Add CaCO3 and the acid solution together in the conical flask and put the bung on the top immediately o Time the reaction and record readings on the gas syringe every 20 seconds for 3 minutes o Repeat the experiment with different acid concentrations Fair Test? The following things are factors that may affect how fair and reliable the experiments are: Things I will change Things I will keep the same Concentration of acid Surface area of CaCO3 Mass of CaCO3 Volume of acid solution Time intervals Temperature Range The range will be as follows; for 25cm3 of acid there is 5cm3 of water, for 20cm3 of acid there is 10cm3 of water, for 15cm3 of acid there is 15cm3 of water. As the amount of acid decreases by 5 cm3, the amount of water increases by 5 cm3, causing the acid to become more dilute. Volume of acid Volume of water Concentration (cm3) (cm3) % 25 5 83 20 10 67 15 15 50 10 20 33 5 25 17 Reliability I will repeat the experiment a further 2 times and then, to ensure that my results are as accurate and reliable as possible, I will work out the average (mean results) of the 3 sets of readings. Prediction I predict that when the concentration is increased the rate of reaction will also increase. I predict this because when there is a high concentration particles are crowed and packed together, causing them to collide more often so more successful collisions occur. When there is a low concentration the particles are more spread out so collide less, therefore less successful collisions occur. Below is a diagram showing the collision theory and the differences in reaction rates with high and low concentration. [image] I have also used the results from my ?Disappearing Cross? experiment to help me come to this prediction. As you can see in the graph below showing the results I collected from the experiment this shows that the greater the concentration the faster the reaction time. [image] As you can see here the graph shows a correlation between the concentration and time taken for the cross to disappear. It shows that the higher the concentration the quicker the reaction time, supporting what I predict will happen with the experiment between hydrochloric acid and calcium carbonate. Results The result table on the previous page shows the results I collected during the experiment. Analysis Of Results My table of results collected from the experiments done show that as the concentration of acid increases the rate of reaction also increases. This is because when the concentration is increased there are more molecules to react causing more successful collisions and the quicker the reaction energy is used up, causing there to be a faster reaction time than there would be if the concentration was lower. The results show what they do as when there is a high concentration there are more particles which are crowded together and are more likely to collide, thus causing more successful collisions to occur. There is a mathematical pattern in my results, and this is; Doubling X doubles Y As the concentration is increased, the rate of reaction also increases, and when the concentration is decreased, the rate of reaction also falls. You can see this in the two measurements when we doubled the concentration, I have take the first reading of how long it took to collect 20cm3 of gas; Volume of HClcm3 Volume of H20cm3 Time taken to collect 20cm3 gas (s) Concentration (%) 20 10 24 67 10 20 13.7 33 As you can see the lower 33% concentration took 13.7 seconds to collect 20cm3 of gas, and the higher 67% concentration took 24 seconds to collect the same amount of gas. This is roughly double the first amount collected, proving the theory that doubling X doubles Y. These results support my earlier prediction, as this is what I thought would happen when the concentration was increased. Evaluation The results collected are quite reliable as the experiment was repeated 3 times and averages were taken from those results to make them as dependable as possible in the time that we had. However, despite having fairly accurate results we did the minimum that is needed for substantial and trustworthy results. Because of the way that we set up our table you cannot see mathematical patterns clearly. One way of improving this and doing a reliable, more precise experiment would be to use these concentrations of acid; o 10% o 20% o 30% o 40% o 50% o 60% o 70% o 80% o 90% o 100% This would help as the concentrations go up in more logical steps of 10% between each concentration, letting any mathematical patterns to become more visible. Also the marble chips used in the experiments were different each time and varied in size, from>0.5cm to <2cm this caused them to have different surface areas which may affect the rate of reaction. A way to overcome this problem would be to use the same marble chips each time, after the reaction you could wash them off and re-use them. The gas syringe was also a problem as it had a tendency to stick if the clamp holding it was too tight, this may be the cause for some unusual results recorded, as this problem was only discovered when we were on our third experiment, which was 15cm3 of HCl. As you can see on our graph the axis showing the experiments done with 15cm3 and 20cm3 of HCl are very close and according to the general pattern in results, shouldn?t be. Ways of avoiding the gas syringe sticking would be to make sure that the clamp isn?t too tight around it or you could use a different method of collecting the gas, where you fill a measuring cylinder full of water and place it upside down in a water bath with a tube that the gas can travel through and displace the water in cylinder, allowing you to measure the gas collected. Another error that may have occurred is a transcription error, where someone may have written down incorrect results or misread the stopwatch or gas syringe. There will also be timing errors where the stopwatch was started at different points or the bung hasn?t been put on the conical flask quick enough but these are just because of human reactions and are generally unavoidable. In summary I think that the experiment we did was sufficient for the purpose we needed and concluded the theory that Higher concentration = Quicker reaction

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