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Assess the effect of concentration of sodium thiosulphate in the acid/sodium thiosulphate reaction

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Introduction

Chemistry Coursework Plan In this project, I am trying to assess the effect of concentration of sodium thiosulphate in the acid/sodium thiosulphate reaction as follows: - Sodium thiosulphate + hydrochloric acid ==>Sodium Chloride + Sulphur + Sulphur dioxide + water Or Na2S2O3+2HCl ==>2NaCl + S + SO2 + H20 Some of these chemicals are hazardous unless handled correctly - here is a safety table of the substances I am using:- Chemical Hazard Procedure Sodium Thiosulphate - Na2S2O3 * Harmful if ingested in quantity * In reactions with acid - Sulphure dioxide is produced. * Ventilate room Hydrochloric Acid - Hcl * Corrosive * Irritant * May cause burns * Vapour is very irritating to the respiratory system * Wear protective clothing * Ventilate room Sulphur Dioxide - SO2 * Irritant to respiratory system * Noctious gas * Ventilate room Sodium Chloride - NaCl * Irritant * Harmful if ingested in quantity * If contact with skin occurs, wash thorugly. Sulphur - S NO HAZARD N/A Water - H20 NO HAZARD N/A To do this I am attempting to measure the speed (time period) in which it takes the colloidal effects of the reaction to reduce visibility of a black cross marked underneath. In order to start the experiment, I will need the following apparatus: - * Conical flask * 10ml + 100ml Measuring cylinders * A4 paper (white) ...read more.

Middle

1-3oc). The same person will always look at the cross to ensure consistency when observing. I am choosing to use measuring cylinders to measure liquid volumes in this experiment as I feel beakers are too inaccurate and none of the small size required are available. Measuring cylinders are the right size, and have appropriate intervals between markings to allow precision when using the liquids. I am also not using pipettes as I do not need the reverse to the above; acutely small amounts. A pipette would rather hinder, than help my experiment by increasing the time required to set up each experiment as I have found with previous experiments involving small measurements. I shall repeat each experiment three times so as to get an average and make the results fair. Prediction I think that as the concentration of sodium increases, the time taken for the cross to become indistinguishable will diminish exponentially as this graph shows: - I think this will happen because the particles in the liquid will have a larger chance of coming into contact with one another and creating colloidal sulphur that will block the view of the cross by reflecting light. Colloids are created during the reaction. A colloid is halfway between a solution and a suspension. In a colloid, particles of matter measuring between about one-millionth of a millimetre and one-tenth of a millimetre in diameter are evenly scattered throughout liquid or gas. ...read more.

Conclusion

This was because a more concentrated liquid has a larger ratio of particles to water. This meant that the acid molecules were more likely to come into contact with the sodium, and therefore create a greater rate at which colloids were produced. We had anomalous results as we had to change our cross after the first five experiments, which changed the time scale. Also, the judging by eye technique was inaccurate and crude. We could not add the liquids together evenly (only by pouring), and the timer was started at small discrepancies with when the liquid was mixed. Also, not all of the acid and mixed liquids came out of the beakers, making it more inaccurate. We could have improved it greatly by using a photosensitive diode to measure colloidal opacity and a computer-controlled timer would have enhanced our readings. Another way of combing the liquids evenly and without having to use physical means (for instance, a Y tube design with holders at the top would have kept time discrepancies to a minimum. Also, greasing/cleaning the equipment thoroughly would stop droplets of liquid clinging to the Pyrex containers. We had results to confirm our conclusion, as the points were relatively straight and 80-90% on the line of best fit. A way to work out reaction time by mathematical means would have been a benefit, cutting out any practical experiment, and eliminating any chance of odd results. ...read more.

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