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Sodium thiosulphate and hydrochloric acid Investigating how the rate of reaction is affected by Temperature.

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Introduction

Investigating the rate of reaction Preliminary work Aim The aim of my preliminary work is to find out how the concentration of sodium thiosulphate, affects the rate of reaction, when added to hydrochloric acid. Prediction I predict that the more dilute the sodium thiosulphate is, the longer the rate of reaction will be. I think this will happen because there will be less thiosulphate particles to collide with the hydrochloric particles and therefore less of a reaction will occur. There will be fewer particles that will be able to hit a point of activation energy that is needed for a good collision. (The rate is the amount of time in which the solution becomes cloudy) Apparatus: - Two conical flasks - One beaker - Two 100 ml measuring cylinder - Black cross - Stop clock - Goggles - Sodium Thiosulphate (Na2S2O3 (aq)) - Hydrochloric acid (HCl (aq)) - Thermometer Method 1. Put Goggles on 2. Gather all equipment together 3. Measure the room temperature 4. Assign each member of the group with a certain job 5. Pour amount of sodium Thiosulphate needed for all the experiments in one conical flask (label it "sodium thiosulphate" 6. Pour amount of hydrochloric acid (label it "hydrochloric acid") 7. For first experiment put 10 ml of acid in one measuring cylinder 8. No water is added 9. Place the black cross under the flask 10. Pour in 50 ml of sodium thiosulphate into flask 11. Pour in 10 ml of hydrochloric acid into flask then immediately timing 12. Judge the appearances of the cross until it disappeared 13. Then stop the clock 14. Record the results 15. Clean the flask out and repeat for all experiments 16. Average out results in a table 17. Then work out the rates 18. Put results into graphs. In the preliminary work a range of concentrations were tested to ensure that when the experiment is carried out and the results recorded the range of concentrations would give good accurate results, with a range wide enough to make a fair test and give a correct conclusion. ...read more.

Middle

Measure the temperature of the start, middle, and end of the reaction 13. Record the results 14. Repeat this for each temperature 3 times. Observation: All rate of reaction experiment have visible results and this experiment is no exception. When I added the hydrochloric acid to the flask I observed immediately at each temperature to see the changes or reactions that were taking place between the particles. When observing the experiment, the changes I saw take place were the tone of the sodium thiosulphate/hydrochloric acid solution. At the initial temperatures, which were quite low, the solution became very foggy and misty but only after a fairly long time the cross was not visible. At the higher temperatures, the solution became fogy very quickly and in both cases, the solution continued to get foggy until the black cross was not visible. I could not see through the solution at all. The colour of the solution went from a clear colourless liquid to a yellowish-green colour and at the higher temperatures, the colour changed almost immediately. I did not see any gas given off or any vigorousness in the actual reaction. The change in colour was smooth and there was no sound made when it happened. Fair Test: To make my experiment a fair one, I had to look at a lot of things. Firstly, I looked at the factors that may have affected how well the investigation would work and these were things like using different equipment or doing the actual experiment in different conditions i.e. a colder/hotter environment. To combat this, I made sure that upon repeating the experiment, I used the exact same equipment and done it in the exact same environment to make absolutely sure that the experiment was fair at each temperature. I think that these were both very important factors because they could affect the results severely and leave me with an anomalous when I should only have correlating results. ...read more.

Conclusion

This would show greater depth into the topic and hopefully provide more conclusive results as to the conditions needed for the optimum yield of the increase in temperature would also decrease the rate of reaction. From background research it is possible to discover that a rise in temperature increases the rate of enzyme-controlled reactions; a fall in temperature slows them down. In many cases a rise of 10oC will double the rate of reaction, but above 50oC the enzymes, being proteins, are denatured and stop working. Knowing this it is possible to compose an experiment which will test if the above information is true for the enzyme, catalyst and work out the temperature at which the rate of reaction is highest. Prediction It is predict that the enzyme catalyst will only work at temperatures above 10oC and below 50oC. The optimum reaction rate will lie somewhere between 30oC and 40oC. As catalyst is an enzyme, which is used in the body, it is likely to have a high yield at 37oC, which is body temperature. The predicted graph shows how the rate of reaction doubles as the temperature increases by 10oC and how below 10oC and above50oC the catalyst is denatured and does not function. Method The apparatus would be set up in the same way as the experiment for substrate concentration only using an ice bath or Bunsen burner to get the catalyst solution to the required temperature. 1. Use 10cm3 of the catalyst solution and place in a chronicle flask. 2. Cool to 10oC using an ice bath. 3. Put 10cm3 of hydrogen solution into the chronicle flask. 4. Leave to react for 1 minute. 5. Record the results. Repeat for 20, 30, 40, 50 and 60oC. Work out average O2 produced for each temperature and rate of reaction. Draw graphs using the results collected. From the graphs conclusions can be drawn as to the nature of catalyst and the best conditions needed for the fastest reaction rate. ?? ?? ?? ?? Verdi Viela science coursework ...read more.

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