An investigation into the factors that affect The rate of reaction between Sodium Thiosulphate & Hydrochloric Acid

MAKING IT A FAIR TEST: I will make it a fair test by-  Repeating the experiment so that I can take an average result so that I can eliminate any anomolous readings. Using a measuring cylinder so that I can measure the quantities accurately. Start the stopwatch as soon as I mix the solutions. Stop the stopwatch as soon as the x disappears. Only change one thing per investigation so that I can see what is making the change if any.

SAFETY: to make sure that I and others around me are safe during the experiment I will- always wear goggles and make sure others are doing so, never sit down at the bench as the acid could fall on me,  keep bags and other items out of the way so that I don’t trip over, wear a lab coat to protect clothing, be careful when handling corrosive or harmful chemicals. Be careful when handling glass.

PREDICTION: I think that increasing the concentration of Sodium Thiosulphate will mean that the reaction will speed up. I think this because before two particles can react they must meet. If the Sodium Thiosulphate is at a low concentrate the Sodium Thiosulphate particles will be widely spread in the water so fewer collisions will occur. At a higher concentrate the Sodium Thiosulphate particles are closer together because there is less water for them to move around in so more collisions will occur so the reaction will take less time. I think that the product of the reaction is a precipitate which clouds the solution because I am looking at a laminated cross through the solution and stopping timing when the cross disappears.

 ANALYSIS MY RESULTS: when you mix the clear liquids of Sodium Thiosulphate and Hydrochloric acid they react to form a yellow precipitate of sulphur. The sulphur starts to form immediately, but takes a while for there to be enough sulphur (product) to make the cloudy precipitate thick enough to hide the cross. The equation shows the reactants and products in this reaction. Na S O + 2HCl 2NaCl +SO +S +H O The graph shows a linear negative correlation showing my prediction was correct- the more concentrated the solution the quicker the reaction would occur. The more concentrated the solution of Sodium Thiosulphate the quicker the reaction occurred because there were more sodium thiosulphate particles so a bigger chance the hydrochloric will meet a particle and react. Using a lower concentration took much longer for the solutions to react than a higher concentration because the particles were more widely spread in the water so the number of collisions between the sodium thiosulphate and the hydrochloric acid were be limited. This would mean that if this experiment was being done for industrial purposes a higher concentration would be used because it reacts quicker. Although if you used a really high concentration the reaction wouldn’t be very successful because there would be too much sodium thiosulphate to react with the hydrochloric acid. This is called saturation. At a low concentration the number of collisions is relatively low, as the concentration is increased the number of collisions increases. Eventually the amount of sodium thiosulphate particles matches that of colliding particles so they cannot react anymore. This would mean that the reaction would not go any faster. To increase the speed you would have to increase the amount of hydrochloric acid so that there would be more hydrochloric particles to react with the sodium thiosulphate. From looking at my graph, at 0.25 moles the time for the reaction was still dropping; so you could still increase the concentration and the time for it to take place would decrease. Although I don’t think you could increase the concentration by too much because the time is already starting to level out.

EVALUATION: I think that the experiment was very successful. It think this because I had no odd readings and the results matched my predictions and corresponded with the research I did to make my predictions. I think that the results were reliable because I repeated the experiment and in both tests the time taken was nearly the same each time. There were no anomalous results. Using a lower concentration took much longer for the solutions to react than a higher concentration. This fitted in with my prediction and research. The sources of error in the experiment could be- The temperature of the solutions could have been slightly different, this could change the results slightly as a slight increase in temperature could give the particles more energy so there is more chance of a successful reaction. The conical flask could have been contaminated, if there was something in the flask before I used it or I didn’t wash and dry it properly between each experiment it could change the results. The timing wasn’t very accurate, as it was hard to decide when the flask finally disappears.  The measuring might not have been as accurate as it could have been, if there was slightly more of one thing than in the previous experiment it would have made it an unfair test and our results would have been unreliable . When adding the solutions together one time they might have mixed quicker than another time, this would mean that the time could be unreliable because the reaction could have started earlier. It is hard to know when the solutions have fully reacted this is why we use a piece of paper with a cross on it to time how long it takes for the precipitate to appear. To make the results more reliable you could use a logit sensor. This is a light beam that penetrates through the solution when the precipitate becomes too thick so that the light beam cant get through this time is recorded on a computer. This means that the time taken will be a lot more accurate because you don’t have to rely on the peer reactions of a human. It was hard to start the stopwatch as soon as the solutions were added together. You could use the logit sensor to make it more accurate. To further develop the investigation you could investigate-  How much you could increase the concentration of sodium thiosulphate without the solution becoming saturated.  Changing the temperature- changing the temperature could help speed up the reaction because higher temperatures give the particles more energy so they move around quicker so collide with each other quicker and with more force increasing the chance of a successful reaction.