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Science Investigation: HCL & Sodium Thiosulphate

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Investigating the rate of reaction between Sodium thiosulphate and Hydrochloric acid Aim I am going to investigate how changing the concentration of sodium thiosulphate affects the rate of reaction with Hydrochloric Acid. I am going to time how many seconds it takes until you can no longer see the black cross on a piece of paper under the beaker. Each time I do the experiment, I will change the amount of sodium thiosulphate and water in the reaction mixture. I want to find out if the concentrated sodium thiosulphate makes the reaction faster or not. When sodium thiosulphate and hydrochloric acid are mixed, a yellow precept of sulphur is produced. The solution becomes increasingly difficult to see through as more and more sulphur is formed. We can measure how fast this reaction occurs by drawing a cross and placing the reacting mixture over it in a clear conical flask. We then observe the time it takes for the cross to disappear (due to the formation of sulphur turning the mixture cloudy) to get an approximate reaction time. Equation Preliminary Results In the preliminary I worked out to make it a fair test I would place a black cross underneath the experiment. To no when to the solutions has become completely cloudy and the reaction has reached the point I am measuring to. Volume of sodium thiosulphate (ml) ...read more.


I will also make sure that the timer is started and stopped at the same point of the experiment and solutions will be made as accurate as possible to ensure that tests correlate with each other better. Safety Throughout this experiment, many risks may arise. I will make sure I wear safety glasses at all times to minimise the risk of chemicals entering my eyes and damaging them. I will also make sure that I know how and when to alert my teacher if a problem does occur, such as broken glassware or chemical if it spills. I will also use a heat mat so that the heat will not be damaged if there is a chemical spillage. Method 1. Measure 50mlof Sodium thiosulphate and 10ml Hydrochloric acid and pour them into separate beakers, making sure you take note of which chemical is which as both are colourless 2. Place the conical flask onto the black cross so that you can see it through the base of the flask. Set up the timer and pour the two chemicals into the conical flask. Start the timer immediately. 3. Keep an eye on the black cross through the top of the conical flask. When you can no longer see the cross through the solution, stop the timer. 4. Record the results and repeat with other concentrations of Sodium thiosulphate. ...read more.


There were a few outlier results, which could be a bit closer to the line of best fit, though they were not too bad (e.g. 35% concentration for the reaction rate graph.) My first sets of results for the 50% concentration were too high compared to my other results, so I had to them again. It later reminded to me that I had done the test at a different time of day to the other results, so I had a different temperature. This would have affected my results, so the new results were done at roughly the same time of day, and therefore same temperature. I also made a mistake in calculating the reaction rates of the sulphur the product which was made in the reaction as I mistyped the result into my calculator and got a completely outlier result. This was put right as soon as I noticed the error. The temperature may affect the results and make them faster or slower depending on the temperature the chemicals are stored at and the room temperature and finally, I believe that my investigation has proved that concentration has an affect on the results as well. Using a measuring meant that my solutions were not as accurate as they could have been, e.g. when calculating 5ml volume in my preliminary results, the 10ml cylinder would have an error of 0.1ml one way or another, calculating as 20% difference, as seen in the formula below: % Error = 0.1 x100 5.0 ?? ?? ?? ?? ...read more.

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