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Reaction between sodium thiosulphate solution (Na2S2O3) and dilute hydrochloric acid (HCl)

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The reaction between sodium thiosulphate solution (Na2S2O3) and dilute hydrochloric acid (HCl) can be used to investigate the affect of concentration upon reaction rate. The equation for this reaction is: Na2S2O3 + 2HCl 2NaCl + H20 + SO2 + S The concentration of Na2S2O3 is 0.16 mol/cm3 and the HCl is 2 mol/cm3. You must use 50cm3 of sodium thiosulphate solution each time and 5cm3 of hydrochloric acid. The reaction is carried out in a flask placed on a piece of white paper, which has a cross upon it. During the reaction a yellow precipitate of sulphur is formed. At the beginning of the reaction the cross can be seen easily. As the flask becomes more and more cloudy the cross gets harder to see. You can measure the time from the start of the reaction until the cross can no longer be seen. This is the rate of reaction i.e. the rate of sulphur formation. I am going to use the investigation between dilute hydrochloric acid and sodium thiosulphate to investigate the affect of concentration upon reaction rate. The rate of a reaction tells us how quickly a chemical reaction has taken place. ...read more.


There is a second reason why the rate increases. Some colliding particles don't bang together hard enough to start a reaction i.e. they don't have enough energy. At higher temperature the particles are moving faster consequently they crash together harder and there are more successful collisions. Catalysts also increase the rate of reaction. The energy needed to start a reaction is called the activation energy. A catalyst lowers the activation energy so that a collision needs less energy in order to be successful. Hence more collisions become successful and so the reaction goes faster. I predict that as the concentration of sodium thiosulphate increases the rate of reaction will increase. Increasing the concentration of a solution means that there will be more particles per dm3. The more particles that there are the more will collide per second and so the rate of the reaction increases. The collision theory states that for a reaction to occur particles have to collide with each other. Not only do particles need to collide but they also need to collide with enough energy otherwise they just bounce off each other harmlessly. ...read more.


Place a conical flask on top of this X 3) Measure 50cm3 of Sodium Thiosulphate using 1 of the measuring cylinders 4) Add to the conical flask 5) Using another measuring cylinder measure 15cm3 of Hydrochloric acid 6) Add to the conical flask, swirl the contents and start the stopwatch immediately 7) Stop the stopwatch when the mixture has turned sufficiently cloudy so that the letter X can no longer be seen 8) Record the time in your results table 9) Repeat the experiment for all of the six concentrations, using the last measuring cylinder to measure out the water 10) Then repeat the whole procedure so that there are two sets of results for each concentration and take the average 11) However if one of the sets of results is entirely different to the other, perform a third experiment to replace the anomalous result. A pair of goggles will be worn during the experiment in order to protect the eyes. And as an extra safety measure bags will be put away and stools pushed below benches. I will record my results in a table, like the one below. Volume of H2O Volume of Na2S2O3 Time (S) Concentration of Na2S2O3 Rate - 1/time (cm2) (cm2) 1 2 Average (moles/dm3) (1/secs or S-1) ...read more.

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