The Effect of Concentration of Hydrochloric Acid on the Rate of Reaction between Sodium Thiosulphate and Hydrochloric Acid

The Effect of Concentration of Hydrochloric Acid on the Rate of Reaction between Sodium Thiosulphate and Hydrochloric Acid
I am going to be investigating the effect of varying the concentration of Hydrochloric acid on the rate of reaction between Sodium thiosulphate and Hydrochloric acid. Chemical reactions can be affected by: Ÿ Changes in the surface area of solid reactants Ÿ Changes in concentration Ÿ Changes in pressure (with gases) Ÿ Changes in temperature Ÿ Catalysts Ÿ Light But I am changing the concentration, as it is the most practical experiment to carry out in a school laboratory. I could have changed the temperature but I have done that experiment before in class. When carrying out my experiment I need to make sure I follow the following safety precautions: Ÿ To keep my lab coat fastened as the laboratory is very crowded. Ÿ Keep the experiment area clear and tidy to avoid spillages as hydrochloric acid is corrosive and can damage the bench. Ÿ Wear safety goggles so that the corrosive acid doesn?t get into my eyes. Ÿ Tie back my hair so it doesn?t get it in the way. Ÿ I must report any accidents to the teacher immediately, as HCl and Sodium thiosulphate can be dangerous substances, broken glass can cause injuries. Ÿ Wash my hands after practicals involving chemicals, HCl is corrosive and dangerous if left on skin for too long.There aren?t enough fume cupboards for everyone in the class to use. I will be using gcse Chemistry textbooks and class notes for information for research, which will be secondary quotes. From experiments I have done in class using Sodium thiosulphate and Hydrochloric acid.
I added 5cm of Hydrochloric acid to 10cm of Sodium thiosulphate with 40 cm of water. I expect the solution to turn from a clear solution to a creamy yellow cloudy liquid, which has an unpleasant smell. I know that the term concentration is the amount of a particular substance within a solution or mixture. The rate of reaction is the rate of formation of a substance or loss of a reactant during a chemical reaction. The rate is for finding the gradient. gives you the measurement of the slope, which is the gradient. is directly proportional to the rate. In my experiment, the volume and concentration of Sodium thiosulphate is the constant and the concentration of the Hydrochloric acid is the variable. The volume of the Hydrochloric acid is also a constant. I also carried out some preliminary investigation to see which equipment I should use to get the best possible results. I carried out the experiment using the same two substances, but I used different pieces of equipment to measure the different amounts of both liquids with . In the end I decided to use the following equipment for my experiment: Ÿ 20 cm of Sodium thiosulphate Ÿ 10 cm of Hydrochloric acid of concentrations of 0.5, 1.0, 1.5, 2.0, 2.5 Ÿ 2 labelled measuring cylinders to measure the Sodium thiosulphate and Hydrochloric acid Ÿ 5 labelled beakers for all the different concentrations of acid Ÿ 1 beaker for Sodium thiosulphate Ÿ Piece of paper with a black cross on it Ÿ A stopwatch I am using 20 cm of Sodium thiosulphate and 10 cm of Hydrochloric acid as they aren?t too much or too little amount of solutions. The amounts are also easy to measure. The measuring cylinder that I am using for Hydrochloric acid will be up to 10 cm so it will be more accurate. The measuring cylinder that I am using for Sodium thiosulphate will be up to 20 cm so it will also be more accurate. I will label the beakers and measuring cylinder so that I don?t muddle up solutions From my practice experiment I am expecting that the more concentrated acid will react faster than the more dilute acid. From my class work I have found that dilute solutions react more slowly than concentrated ones because many of the collisions involve solvent molecules. method Take 20 cm of Sodium thiosulphate in a beaker , measured with a measuring cylinder and put it on the piece of paper with the cross on it. Add 10 cm of Hydrochloric acid. Start the stopwatch as soon as all the acid is in. Keep looking into the beaker from above, when the cross has disappeared, stop the watch and record the time in seconds. There is an equation for this experiment: Sodium + Hydrochloric = sulphur + sodium chloride + sulphur dioxide+ water Thiosulphate acid The experiment should be carried out fairly and I need to consider the following. I must make sure that the beaker I use is always the same size, if the beaker is narrow, there is more solution to look through than a wider beaker and the cross will take longer to disappear. E.g: I also need to make sure that the lighting is the same as it may affect when I notice the cross has disappeared. Eyesight can also be a problem so I must make sure I wear my glasses underneath my safety goggles. When I wash out my beaker and use it again I must dry it properly using a paper towel as the water may make the solution more dilute. And also wash the beaker with normal temperature. If I wash it with hot water, the reaction may happen faster. From my previous experiment I found that higher temperatures make reactions happen faster. When investigating surface area, I found that with greater surface area of solids, collisions are more frequent. There are more collisions so the reaction rate is quicker. At high temperatures particles are moving faster, there are more collisions. The collisions are also more energetic. Here are results from my experiments with temperature: Temperature /seconds Time/seconds Time/seconds Time/seconds Average/ seconds Rate/seconds 20 236 281 278, 274 278 0.0036 30 144 141 142.5 0.007 40 66 64 65 0.015 50 35 48 36 35.5 0.028 The experiment is being done in room temperature so the temperature will be as controlled as it can be. I must make sure that all the equipment I use to measure must be the same, some equipment measures more accurately than others. All these factors can affect experiments and should be controlled as well as they can be. I am going to take measurements of the time taken for the cross to disappear for each different concentration in a table like below: Concentrations of Hydrochloric acid (mol/dm) Time taken (seconds) Repeat (seconds) Repeat (seconds) Average time (seconds) 0.5 1.0 1.5 2.0 I will do repeats for my experiments if the first two results are very far apart. Repeats are necessary as the first result may be wrong because of a simple mistake, such as starting the stopwatch too early or late, or using the wrong concentration of acid. After drawing this table, I will plot a graph with concentration against time taken. This will tell me to show whether the time taken increases or decreases when the concentration increases. I will then find the mean average of the 3 results and then find the rate of reaction. The rate of reaction is measured by dividing the time taken by 1. ( ) I will write it up in a table like below. Then I will draw a graph with Concentrations of Hydrochloric acid against Rate of reaction Concentrations of Hydrochloric acid (mol/dm) Average time (seconds) Rate of reaction (seconds) 0.5 1.0 1.5 2.0 2.5 From research in textbooks I have found that in order for a reaction to occur, particles have to collide with each other, this is the collision theory. Increasing the concentration of hydrochloric acid can increase the frequency of collisions. ( Chemistry, Hunt and Sykes) I predict that when the concentration of Hydrochloric acid is increased so will the rate of reaction. There will be more molecules of Hydrochloric acid, which will be able to collide and react. I also predict that the graph with concentration against time taken will have negative correlation as the time taken decreases, as the concentration gets higher. The graph will be a curve. I predict that the graph with Concentrations of Hydrochloric acid against Rate of reaction will have positive correlation as the rate of reaction will probably increase with higher concentrations. The graph will probably be a straight line, but not a perfect straight line. The rate of reaction won?t go up exactly the same. I will measure the time taken in seconds, the rate of reaction in seconds and the concentrations of acid in mol/dm . I predict that my graph for concentration and time will look like this: I predict that my graph for concentration and rate will look like this: I carried out my experiment like I said that I would. I followed all of the safety precautions, I did not spill or break anything so did not have to call the teacher. Results This is my table for the acid and time taken for the cross to disappear: Concentrations of Hydrochloric acid (mol/dm ) Time taken (seconds) Repeat (seconds Repeat (seconds) Average time (seconds) 0.5 63 60 60 61 1.0 46 47 48 47 1.5 43 43 43 2.0 38 39 38 38.3 2.5 36 37 36 36.3 For the results of acid 1.5 mol/dm I have only done 1 repeat as both results were the same and probably accurate. For the results of acid 0.5 mol/dm I thought 62 and 61 seconds were a bit too far apart so I did another repeat. I will have to round down the 36.3 and 38.3 for my graph, as it is the closest I can get on my graph. I did try out more results to see whether the range was bigger, but it wasn?t so I used these initial results for analysis. I changed the ratio from 1:2 to 1:4. The range of the other results was from 34seconds with 0.5 HCl to 24 seconds with 2.5 HCl. This was using 40 cm of Sodium thiosulphate and 10 cm of Hydrochloric acid. The range for these results is from 36 seconds to 61 seconds. This makes a difference of 24.7 seconds which is quite a good range of results. All my repeats were quite close together so they must be quite reliable and accurate. I had outliers in my experiment which I could clearly see from my graph. Graph 1 shows quite a smooth curve negatively correlated, showing that the time taken for the reaction to occur decreases as the concentration is higher. This matches my predictions, I predicted that the time taken would decrease as the concentration increased, and that the graph would be negatively correlated and a curve. All but one of the results fit on the smooth curve, suggesting an accurate method. I missed a result out in my curve, to draw a line of best fit. The result is the 43 seconds for 1.5 concentration for Hydrochloric acid. It should have been a few seconds faster to make a perfectly smooth curve. When I was washing out the beaker I must have left some water in it which slowed down the reaction, the concentration would become more dilute. Here are my results showing the average times and the rate of reaction: Concentrations of Hydrochloric acid (mol/dm) Average time (seconds) Rate of reaction (seconds) 0.5 61 0.016 1.0 47 0.021 1.5 43 0.023 2.0 38.3 0.026 2.5 36.3 0.028 To find the rate I used and for time I used the average time. Graph 2 shows positive correlation and is a straight line of best fit. This time the outlier fits in the line of best fit. This shows that the rate of reaction increases as the concentration is higher. This graph shows that the rate is almost directly proportional to the concentration. This also matches my predictions as I said that there would be positive correlation and a straight line graph. I also said that the rate would increase with concentration. I am sure that if I changed the Sodium thiosulphate concentration the results would show an increase in rate of reaction with the more concentrated Sodium thiosulphate. There isn?t really a trend in the results as the time taken decreases by 14 seconds from the first two concentrations. Then it goes down by 4 then 4.7 and finally 2 seconds. . The rate of reaction increases by 0.005 then 0.002, then, 0.003 and 0.002. There is a bigger difference in the time taken between 0.5 and 1.0 mol/dm of Hydrochloric acid and then the difference rapidly decreases. There isn?t really a pattern. Even the Rate has quite a big difference which then decreases but only slightly. For this to fully make sense it is necessary to recap the collision theory briefly: For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is because of the energy barrier they have to overcome. Only particles with enough energy to overcome the barrier react after colliding. The activation energy (Ea) is the minimum energy that a particle has to overcome, it is like a barrier. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percentage of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure and surface area. Evaluation My results were quite reliable as I went along with my plan and did repeats. I also used my graphs to eliminate the outliers and suggested reasons for the results. My graphs showed that the method was quite good. I could have made my method better to get more accurate results. But we were in a school laboratory where there is limited space and equipment. I could have used a syringe or a burette which are more accurate for measuring than measuring cylinders which don?t show as precise measurements. I could have done 4 repeats for each result and then seen which results were odd and not used them when calculating the average. Also to produce graphs with more accurate lines of best fit I could have used more concentrations. By taking 0.5 and 1.0 mol/dm of Hydrochloric acid and adding the same amount of water, then plot the points, it will show whether the graph is a straight line or a curve. When doing experiments in the laboratory people are bound to make mistakes so if they were available I could have used a data logger, light meter and computer to ?watch? the experiment and the computer plots the graph simultaneously as the light meter detects that the reaction mixture is getting darker. This is how the equipment would be set up: But this equipment is quite expensive and harder to set up, also the factor of adding too much or little of the solutions is still there so the results still wouldn?t be totally accurate. Another thing I could have done to bring more evidence is to have tried to use the Sodium thiosulphate as the variable substance, and used the Hydrochloric acid as the constant substance. This would have brought more evidence to support the idea that the higher concentration of a substance, the faster it will react.

The Effect of Concentration of Hydrochloric Acid on the Rate of Reaction between Sodium Thiosulphate and Hydrochloric Acid 8.1 of 10 on the basis of 2033 Review.