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Sodium thio sulphate and hydrochloric acid reactions.

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Introduction

Chemistry Coursework Planning Introduction When sodium thio sulphate 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 (r) 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. In this experiment, I hope to find out how the concentration of a solution will affect the rate of the reaction with another solution. I will do this by changing concentrations and observing the effect it has on the reaction. Variables Constant The concentration of ONE of the solutions The concentration of the other solution The size of the cross I make on the paper Fair Test To insure that it's a fair test, I have to insure that I only change the concentration of one solution and keep the other constant. ...read more.

Middle

To break the bonds the start of a reaction, energy is needed. The reactants have to go up the energy scale first before they start reacting. At the top of the curve, the bonds in the reactants have been broken. The amount of energy that broke these bonds is called activation energy (the minimum amount needed for a reaction to occur). A catalyst works by lowering the activation energy for a reaction. In the slope of the curve, heat energy is being given out as new bonds form in the products. The reactants are higher up the energy scales than the products. The amount of energy (heat) you need to put in is less than the amount of heat you get out. This is a typical exothermic reaction. The difference in energy levels between the reactants and products is given the symbol H. This is the amount of energy given out during the reaction. For an exothermic reaction it is negative but for endothermic it is positive. Obtaining Time taken for cross to disappear (mins) Volume of thio sulphate (cm3) Volume of HCL (cm3) Volume of water (cm3) 1 2 3 Average 50 5 0 40 46 39 42 45 5 5 47 49 45 47 40 5 10 50 51 52 51 35 5 15 ...read more.

Conclusion

Any number of things such as could have caused this: * Measuring- the actual measuring of the chemicals is difficult because of the meniscus of the liquid and the accurateness of the measuring cylinders. Also, the human eye causes errors such as this * The eye could also have made mistakes in judging whether 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. This was a good point in my experiment. It made them more accurate than using a measuring cylinder. * 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. See below ...read more.

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