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Rate of reaction- Sodium Thiosulphate and Hydrochloric Acid.

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Rate of reaction- Sodium Thiosulphate and Hydrochloric Acid Introduction When sodium thiosulphate and hydrochloric acid react they produce a cloudy precipitate. The two chemicals are both clear solutions and will react together to form a yellow precipitate of sulphur, the equation for which is as follows: Na2S2O3 + 2HCl ?2NaCl + SO2 + S + H2O As the solution will turn cloudy, we can observe the rate of reaction by placing a black cross underneath the beaker and seeing how long it takes for it to disappear. There are factors that affect this experiment such as temperature, concentration and time. I do not think that surface area will affect the experiment, as both chemicals are liquids. For my experiment I will study concentration as this is easily observed and can be easily varied. Prediction I think that as the concentration of sodium thiosulphate increases, the amount of time taken for a reaction decreases. I know this because before two particles can react they must meet. In a low concentration, the particles will be few and widely spread. This means that the number of reactions will be limited because less particles will meet. At higher concentrations there are more particles and so they probability of them coming into contact with other particles is increased. ...read more.


This is because if I use above 50 the results will not be affected anyway and so a substantial amount of thiosulphate is not obtainable, due to limitations on the school's resources. This is also the best range to use because in my evaluation I will need to discuss further work, and then I could use 5, 15, 25, 35 and 45 to create further results and make my experiment more accurate. Method Take a piece of paper with an "x" clearly marked on it, conical flask, measuring cylinder and timer. Measure 50cm3 of sodium thiosulphate and 5cm3 of hydrochloric acid. Add the hydrochloric acid to the sodium thiosulphate in the conical flask and gently swirl. Place conical flask on the paper with "x" marked and start the timer. Observe the reaction through the top of the conical flask and stop the timer as soon as the cross can no longer be seen. Repeat experiment with 40cm3 thiosulphate, 5cm3 hydrochloric acid and 10cm3 water. Keep repeating, adding 10cm3 less thiosulphate and 10cm3 more water each time. Record results in a table of results. Apparatus Sodium thiosulphate, hydrochloric acid and water Paper with "x" clearly marked. Conical flask Measuring cylinder Timer Results Time taken for cross to disappear (S) Volume of thiosulphate (cm3) Volume of HCL (cm3) ...read more.


Also, the human eye causes errors such as this The eye could also have made mistakes in judging whether or not the cross had actually completely disappeared If the same person watching the reaction was working the timer, errors could occur in their co-ordination. We could remove these errors by: Making sure the bottom of the meniscus is read so that it is the true reading. Using a burette to measure. This would remove the measuring errors associated with measuring cylinders, as they are correct to 0.1 cm where measuring cylinders are only 0.4. Burettes are a far more accurate way of measuring the correct amounts. Use light sensors to detect when the cross is no longer visible. The experiment could be connected to a light sensor, and to a timer. These light sensors will detect when there is no light shining through the substance. This would automatically stop the timer and therefore make the experiment fairer and more accurate. To further investigate this experiment, I could use a wider range of times. I used 10, 20, 30, 40 and 50 and so I could use the mid points of these times for more accuracy. I could also go up to 100cm3 to obtain more results but this possibly would not affect my experiment. Andy Fraser ...read more.

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