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An investigation into the effect of Concentration of Sodium Thiosulphate on the rate of reaction between Sodium Thiosulphate and hydrochloric acid

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An investigation into the effect of Concentration of Sodium Thiosulphate on the rate of reaction between Sodium Thiosulphate and hydrochloric acid Introduction/Background Knowledge: In this experiment, we are investigating how the concentration of Sodium thiosulphate effects the rate of reaction of hydrochloric acid. Sodium Thiosulphate + Hydrochloric acid Sulphur + Sodium chloride + Sulphur chloride + water Na2S2O3 + 2HCl S + 2NaCl + SO2 + H2O For this reaction to take place, the particles have to collide with more energy than the activation level. However, if this collision takes place with little energy, and below that of the activation energy, no reaction will take place. These reactions depend on collisions, and is explained using a collision theory, this states that a rate of reaction depends on the frequency, and strength that the particles collide with one another. There are factors, which affect this, however, including Temperature, Concentration, surface area, and catalysts. These factors increase, or decrease how efficiently a reaction takes place. Description of experiment: In the experiment, as the concentration of Sodium Thiosulphate Increases, the reaction time between Sodium Thiosulphate, and Hydrochloric acid will decrease. This will happen because, the more concentrated the Sodium Thiosulphate solution, the more Sodium Thiosulphate molecules, and the less water molecules. So a Sodium Thiosulphate solution with a low concentration, e.g. 0.2M will take longer for a successful reaction to take place than what it would with a high concentration, e.g. 1.0M. Preliminary Studies: Before completing the main test, I carried out a pre-test, using a conical flask, solutions of Sodium Thiosulphate at concentrations of 0.2, 0.5, and 1.0M, and 1.0M Hydrochloric acid. I carried out this to make sure that I had a large enough range of values (concentration) to carry out an accurate and reliable experiment. Here are my results and analysis from the pre-test practical. We have chosen to use a beaker instead of a conical flask because as a conical flask has a narrow neck, it became difficult to clean in-between uses, making the experiment take longer, and be less accurate if there was any water left in the bottom. ...read more.


along with putting stools under the table; personal belongings need to be out of the way so we have a clear, and safe working area. We need to also be careful of spillage's, as we are working with acids, which can be corrosive. We must wear safety goggles in case there are any splashes from the beakers when we are mixing the two reactants, because of working with acid's and alkalis. Equipment: Equipment: Size/Range: Reason: Tile (with large clear cross) 10cm X 10cm The tile (easily cleaned, not wasting materials, doesn't matter if wet) with cross is needed to see when the two solutions have reacted. Measuring cylinder (X 3) 25 ml These are accurate to 0.5 ml, and are easy to read Beakers (X 4) (1 glass) 250 ml Glass - for the reaction too take place in, allowing for the cross to still be seen Plastic - for making the Sodium Thiosulphate solutions (1 for sodium thiosulphate, 1 for Hydrochloric acid, 1 for water) Pipette 3 ml Accurate to 0.5 ml 1 molar Hydrochloric Acid 225 ml Molarity chosen in pre-test 1 molar Sodium thiosulphate 225 ml Molarity chosen in pre-test (and simple to make varied concentrations from - see preliminary work) Water 150 ml Needed to make varied concentrations of Sodium thiosulphate Stop watch Accurate to 0.01 secs Accurate, needed to time reaction between Sodium thiosulphate and Hydrochloric acid Safety Goggles Safety (see safety section) Method: 1. Check Safety. 2. Draw a black cross onto the white tile with a bold marker pen and put the glass beaker on top so the cross is visible through the base. 3. Carefully measure out the concentrations to make up 25 ml of sodium thiosulphate using a pipette and put it into a measuring cylinder. Read from the bottom of the meniscus when measuring every time so that it is a fair test. If we read from different points on the meniscus we will get a different volume each time. ...read more.


I feel that my results are accurate because my graph has produced a smooth curve, which describes an accurate reaction. I made sure the practical was accurate by only varying the molarity of Sodium Thiosulphate solution, and keeping the molarity of Hydrochloric acid the same. I also used the same volume of Hydrochloric acid as Sodium thiosulphate (25 ml). In the experiment, I controlled the use of temperature, surface area (in experiment pressure), and the use of catalysts. I controlled this by only varying the concentration of one reactant (sodium thiosulphate) and by controlling everything else. Carrying out the experiment over one day, at room temperature controlled the temperature. I controlled catalysts by not using any. As I carried out the experiment on the same day I successfully controlled the pressure of the liquids. We calculated averages when we had collected each set of results because this gave us a mean point to plot on our graph, and a better line of best fit, and reduces inaccuracies. If I was to complete this experiment again, I would use the same method, but use more accurate measuring equipment, for example, titration to make and check the accuracy of concentrations of Sodium Thiosulphate. If this experiment was completed mechanically, it would make it more accurate. The solutions of Sodium Thiosulphate could be mixed more accurately, and as soon as the angle of a measuring cylinder containing the hydrochloric acid was over a certain angle, a stopwatch would begin timing. A light detector ray could be passed through the glass beaker onto a white background, if the ray wasn't detectable by the computer, the stopwatch would be immediately stopped. If this happened, we could use hundredths of seconds because the level of accuracy would be higher, thus making the practical be more accurate and giving us better results. Zoe Wheeler 55227 Rates of Reaction Coursework Zoe Wheeler 55227 Rates of Reaction Coursework ...read more.

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