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To see what factors affect the rate of reaction between Sodium thiosulphate and Hydrochloric acid

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To see what factors affect the rate of reaction between Sodium thiosulphate and Hydrochloric acid Introduction: Sodium thiosulphate and hydrochloric acid react slowly to form a white/cream precipitate that makes the solution opaque. This reaction is not immediate, but gradually the white precipitate (which is sulphur) prevents you from seeing though the beaker to the surface of the bench. Na2s2o3 + 2HCL 2NaCl + SO2 + S + H2O The reaction between the sodium thiosulphate and the hydrochloric acid relies on successful collisions between these two reactants. A successful collision needs three important conditions to be satisfied: - 1) The reactant molecules must collide with each other. 2) The molecules must collide with the correct alignment. 3) The molecules must collide with enough energy to overcome the activation energy. This graph shows the energy needed for the activation energy as the reaction continues. After the activation energy is satisfied energy is given out and the reaction ends with a lower point of energy. When I mention successful collision these three conditions are being satisfied. Variables: Concentration of reactant When you increase the concentration of sodium thiosulphate you increase the number of reactant molecules per unit volume, increasing the chance of particles colliding successfully and in turn increasing the frequency of collisions thus increasing the rate of reaction. When you double the concentration, you double the chance of a collision and double the frequency thus doubling the frequency. The rate doubles when the concentration of the reactants doubles, thus concentration is proportional to rate of reaction. Temperature As you increase the temperature the more energy the molecules have, thus they move faster and collide more frequently. Also the collision has greater energy thus more easily meeting the activation energy, and increasing the rate of reaction. Surface area of the reactants Surface area really only affects the rate of a reaction when the reactants are solids, in this experiment we are dealing with liquids. ...read more.


* For precision and accuracy I will measure out all volumes of liquids in measuring cylinders first. * I will use different measuring cylinders for each liquid as not to contaminate the liquids and begin the reaction too early. * I will need to take a greater range of readings to get a suitable number of readings to produce a graph line to show the proportionality and to reach a firm conclusion. Final Method 1) Take one measuring beaker and designate this the sodium thiosulphate measuring cylinder. 2) Pour sodium thiosulphate into the measuring cylinder until it reaches the 50 ml mark. 3) Pour the HCL into the 10 ml measuring cylinder up to the 10 ml mark. 4) Place the 100 ml beaker upon some printed text. 6) Pour the HCL and the sodium thiosulphate into the beaker and start timing immediately. 7) Observe the beaker constantly and end timing as soon as the text cannot be read. 8) Record the time taken for the reaction to complete. 9) Wash out the 100 ml beaker as not to contaminate the next reaction. 10) This time pour 45 ml of sodium thiosulphate into the designated measuring cylinder. 11) Use the other measuring cylinder as the water one and pour 5 ml into it. 12) Pour the contents of measuring cylinders into the beaker. 13) Pour the 10 ml of HCL into the beaker and begin the timing. 14) Use the same print as before to keep a fair test as differing prints could be lighter or darker. 15) Repeat steps 9-15 but with concentrations 40 ml of thio and 10 ml of water, 35 ml of thio and 15 ml of water etc. Continue changing the volume of thio by 5 ml smaller each time untill you reach a ratio of 10ml thio and 40 ml of water. 16) Do two check readings of each concentration. ...read more.


I feel the that evidence is not enough to support a firm conclusion, as although the results were as predicted, to reach a firm conclusion I would have to investigate reactions between different reactants such as Magnesium and HCL and collect the volume hydrogen given off. Also to reach a firm conclusion, I would investigate concentrations smaller than 20%, to prove proportionality at 10% concentration and below. I would also study reactions that took considerably longer and still see if rate is proportional to concentration. Further work would be to investigate the other variables: - Temperature I could use the same reactants as used for this experiment, but maintaining a concentration of 40% sodium thiosulphate. I would investigate temperatures between 0? and 100?. I would investigate how temperature effected the rate of reaction. Catalysts I would investigate which transitional metals lowered the activation energy of a successful collision the most. One experiment I could do would be to leave hydrogen peroxide in a conical flask with a collecting syringe to collect the oxygen, and leave it to decompose naturally. This would be the control. I would then set up another flask and collecting syringe but with a gram of manganese 3 oxide and see how the transitional compound effected the rate of decay. I would then try different catalysts such as platinum wire and see which is the better catalysts and what properties are needed for a good catalyst. Surface Area I would also investigate different surface areas of reactants, or different pressures of gases and see how it effected rate of reaction. For this experiment I would react calcium carbonate with HCl. I would place the chips in a conical flask with a division. I would attach this flask to collecting syringe. I would start the experiment by shaking the flask and allowing the two reactants to mix. I would study the rate of which the hydrogen is given off. I would the repeat this experiment using the same volume of calcium carbonate but this time use a powder form and study if it gave off hydrogen faster than the chips. ...read more.

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