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Rates of reaction of Sodium Thiosulphate with Hydrochloric Acid

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Chemistry Coursework Rates of reaction of Sodium Thiosulphate with Hydrochloric Acid Michela Nardini Title Sodium thiosulphate and hydrochloric acid reaction rates. Aim To investigate how altering the concentration of sodium thiosulphate affects the time taken for the reaction with hydrochloric acid. Prediction In a reaction of hydrochloric acid and sodium thiosulphate my prediction would be as follows: with the concentration of hydrochloric acid remaining constant, as the volume of sodium thiosulphate decreases and the volume of water increases the reaction time will increase. One would not expect the halving of the concentration of sodium thiosulphate to result in a doubling of the reaction time as volume is three dimensional and not linear. I also predict that there will be a precipitation of solid sulphur. From my research done, sodium thiosulpate and hydrochloric acid will react as in the equation below: Na2S2O3(aq) + 2HCl(aq) 2NaCl(aq) + S(s) + SO2(g) +H2O(l) This chemical balance equation explains that sodium thiosulphate, in an aqueous solution, when mixed and allowed to react with hydrochloric acid, in an aqueous solution, will form sodium chloride in an aqueous solution, solid sulphur together with sulphur dioxide gas and water. The solid sulphur which forms in the solution causes the water to look cloudy. It is interesting to note that sodium chloride is ordinary table salt. ...read more.


This means that the reaction is happening at a slower rate. If the volume of sodium thiosulphate was increased, and the volume of water decreased in order to make 50 cm3 of solution; there would be more frequent collisions of particles with more energy. In this case, the hydrochloric acid and sodium thiosulphate particles would collide and more particles would react. Because the rate of collision is higher the rate of formation of sulfhur and of the reaction is increased. As the sodium thiosulphate collide and react with the hydrochloric acid, the sulphur is precipitated out of the solution. This solid sulphur makes the water look cloudy. Variables table Things I will keep the same Things I will change Things I will measure 50cm3 of sodium thiosulphate and water Volume of the water Time Sodium thiosulphate (0.3M) Volume of sodium thiosulphate Sodium thiosulphate to make the solution Hydrochloric acid (0.5M) Water to make the solution Hydrochloric acid 5cm3 Hydrochloric acid Room temp of all reactants These factors will make it a fair test. Apparatus Hydrochloric acid (0.5M) Sodium thiosulphate (0.5M) 10cm3 Cylinder 100cm3 Cylinder 250ml Conical flask Stopwatch Thermometer Goggles Piece of paper with fine cross Diagram Method 1. Mark a cross, (with a fine pen), on a piece of paper. Place on the table. ...read more.


Firstly, to arrive at a mean time, more data should be collected for each point plotted on the graph. The time at which the stopwatch was started and stopped could be improved. By using an instrument to detect the quantity of light coming through the solution, from a fixed constant light source shining throughout the solution to the light strength detector, we could stop the stop watch at a constant light intensity. The rate at which the acid is added to the sodium thiosulphate should be constant. This means that it should always take the same amount of time to add the acid to the sodium thiosulphate. The temperature at which the reactants were used and added to each other should have been kept constant in order to avoid any changes in the reaction rate. Conclusion When hydrochloric acid was added to the sodium thiosulphate solution, a reaction took place. The rate of this reaction depended on how often, and hard the reacting particles collided. Particles have to collide hard enough for the reaction to be successful. By diluting the sodium thiosulphate with water, and then adding acid, the reaction rate decreased. The reaction rate decreased because fewer molecules, with less energy of sodium thiosulphate were available to collide with the hydrochloric acid particles. Thus, my prediction, that the lower the concentration of sodium thiosulphate, the slower the reaction rate, was correct. Put another way, the lower the concentration of sodium thiosulphate, the more time was required for the reaction to take place. ...read more.

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