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The reaction between Sodium Thiosulphate and Hydrochloric Acid.

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Introduction

Chemistry Coursework The reaction between Sodium Thiosulphate and Hydrochloric Acid Aim: In this investigation, we are trying to determine the effect that changing the concentration of the hydrochloric acid has on the rate of reaction between sodium thiosulphate and hydrochloric acid. We have chosen to measure how long it takes before the solution becomes cloudy and the light beam is no longer detected through it. We can do this by using light gates attached to a computer that will record the results on a graph. Prediction: I believe that the greater the concentration of hydrochloric acid, the less time it will take before the light beam is no longer detected through the solution. When the acid is pure and isn't diluted at all then the reaction should be the quickest. When the acid is the weakest then the reaction will be slower because the concentration of the molecules isn't as much and so there is less chance of a successful collision to cause the reaction. Scientific Information: The rate of a reaction is the amount of a substance that takes part in a chemical reaction in a given time. Chemical reactions happen at widely different rates. The weathering of buildings and statues caused by acid rain is very slow, but the reactions that take place when a firework explodes are very fast. Most reactions take place at a rate somewhere between that of a firework explosion, which is almost instantaneous, and that of weathering stone. Speeding up useful reactions and slowing down harmful ones can be important in industrial production processes, and in activities such as preserving buildings or foodstuffs. The rate of reaction can be calculated by using one of two formulae: Rate of reaction = amount of product forming time taken OR Rate of reaction = amount of reagent reacting time taken There are four factors that change reaction rates: - Temperature: - All chemical reactions go faster at a higher temperature and if reacting substances are heated, the rate of the reaction usually rises. ...read more.

Middle

This will make my results more reliable, providing that the three results I get are quite close together. If the results for the experiments are far apart, then my data will not be very reliable and so my findings will not be as conclusive. My results will show me how changing the concentration of hydrochloric acid affects the rate of reaction between it and sodium thiosulphate. They will tell me how long it took for the reaction to complete and the cross to become invisible through the solution. This will enable me to draw conclusions from my results and compare them to see if my prediction was correct. Pretest: In my pretest, I didn't use the computer because it wasn't set up, and so I conducted the experiment by drawing a cross on a piece of paper and timing how long it took before the cross became invisible. Although this wasn't the way I conducted my real experiment, it gave me the idea of how much of each chemical to use and what concentrations to use so it did help me in that respect. In my pretest, I used 20cm3 of hydrochloric acid and 20cm3 of sodium thiosulphate, instead of using 25cm3 of both. This difference in the procedure was critical in the results that I obtained. The results I obtained were: Concentration of hydrochloric acid (moles) Time taken for reaction to complete (secs) 0.4 39 0.32 47 0.24 52 0.16 58 0.08 63 Because I only used 20cm3 of hydrochloric acid, it meant that I had to measure out complicated volumes in the measuring cylinders, and I may not have measured them accurately enough to get accurate results. You can see this because the numbers of moles are nearly all two-digit numbers. The reason I chose to change my procedure is because I found it difficult to measure out the complicated volumes. I made the volumes 25cm3 instead of 20cm3 so that it is easier for me to measure the amounts. ...read more.

Conclusion

3. Light the Bunsen Burner and heat the water to 40�C, thus creating a water bath for the boiling tubes. Test the temperature using a thermometer to make sure it is at 40�C. 4. While the water is heating, collect the 25cm3 of sodium thiosulphate (and water) and the 25cm3 of hydrochloric acid. Pour the sodium thiosulphate (and water) into one boiling tube and the hydrochloric acid into another and place them in the test tube rack to keep them safe from spilling. 5. When the water is at 40�C, place the two test tubes into the water and wait until they are both at 40�C. Turn off the Bunsen Burner so that they don't heat up anymore. 6. Turn on the computer and check that the light sensor is plugged in and working. 7. Place the bulb, battery, light sensor, and an empty boiling tube in the wooden box in the correct places. Turn on the bulb and line it up with the light sensor. 8. When both the solutions are at 40�C, pour them into the boiling tube in the wooden box simultaneously and start the computer logger. 9. When the graph stops descending, or the total time you allow for the reaction is reached, stop the logger. 10. Save and print the graph so it can be used later. 11. Repeat steps 1-10 for the other concentrations of sodium thiosulphate (and water). Repeat the whole experiment to get more reliable results, but make sure they are still accurate by keeping everything the same as the first time you did the experiment. This method is almost identical to that of the experiment that I actually conducted. This is because all of the equipment would be exactly the same and the set up would be the same. The only things that are changed are the concentrations of sodium thiosulphate and hydrochloric acid and the temperature that the reaction is conducted at. Phil Scott 10V June 24th, 2003 Page 1 of 12 ...read more.

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