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To find the rate of reaction between different concentrations of Sodium Thiosulphate and a constant concentration of Hydrochloric acid and to follow the speed at which Sulphur is formed.

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Introduction

Aim: To find the rate of reaction between different concentrations of Sodium Thiosulphate and a constant concentration of Hydrochloric acid and to follow the speed at which Sulphur is formed. Hypothesis: Rate of reaction is determined by the concentration of reactants. The hypothesis is that the rate of reaction of Sodium Thiosulphate with a constant concentration of Hydrochloric acid will increase as the concentration of Sodium Thiosulphate increases. Equipment used: * Conical flask * Large measuring cylinder (50cm3) - for Water and Sodium Thiosulphate * Small measuring cylinder (10cm3) - for Hydrochloric acid. * Pipette (optional) * Distilled water * Beakers- 1 beaker should be labelled with Sodium Thiosulphate and the other should be labelled with Hydrochloric acid. This is so the two do not get confused for one another. * Thermometer - to measure room temperature * Stop clock * Paper with a cross marked clearly on it * A supply of Hydrochloric acid and Sodium Thiosulphate Safety: * Wear goggles to protect your eyes * Wear a lab coat to ensure that your clothes stay clean * Wear gloves (optional) * Wash your hands after the experiment Procedure: Preliminary work: Table 1 Concentration of Sodium Thiosulphate (mol/l) Volume of Sodium Thiosulphate (mol/l) ...read more.

Middle

The more water added to Sodium Thiosulphate decreases its concentration. Concentration of Sodium Thiosulphate (mol/l) Volume of Sodium Thiosulphate (cm3) Volume of Water (cm3) Volume of Hydrochloric Acid (0.5 cm3) Time 1 (mins + secs) Time 2 (mins + secs) 0.05 10 40 5.0 3min 15sec 3min 12sec 0.10 20 30 5.0 1min 8sec 1min 8sec 0.15 3- 20 5.0 44sec 42sec 0.20 40 10 5.0 30sec 30sec 0.25 50 0 5.0 21sec 20sec Preliminary work: The table above shows the time taken for the cross to disappear with different amounts of concentration of Sodium Thiosulphate and different amounts of volume of both Sodium Thiosulphate and Water. By looking at the time results it is evident to say that the more concentration there is of Sodium Thiosulphate the less times is taken for the cross to disappear. I predict that the production of Sulphur blocked my view of the cross as it appears in the form of tiny particles of solid, and that the particles do not settle they remain in suspension. Sodium + Hydrochloric Sulphur + Sodium + Sulphur + Water Thiosulphate acid Chloride dioxide Na2S2O3 (aq) + 2HCl (aq) S(s) + 2NaCl(aq) + SO2(g) + H2O Discussion: The results show that the cross disappeared the soonest when the solution was at its most concentrated. ...read more.

Conclusion

In this experiment, only one concentration was altered. A variation is to keep the concentration of Sodium Thiosulphate constant and alter the concentration of acid. Then the speed of the reaction is found to be proportional to the concentration of the acid. If the acid concentration is doubled, the speed doubles. The reason for this is that the ions are closer together in a concentrated solution. The closer together they are, the more often the ions collide. The more often they collide the more chance they have of reacting. Reaction rates can be speeded up by: * Increasing the concentration of the reacting solutions; * Increasing the surface area of the contact between reacting materials; * Increasing the temperature of reactants; * Using a suitable catalyst. If we were to extend this enquiry I would increase the concentration of Hydrochloric acid and see if it increase the rate of reaction and how the results differ. Conclusion: With increasing the concentration of Sodium Thiosulphate less time was taken for the solution to become cloudy and Sulphur to be formed. Vice versa decreasing the concentration of Sodium Thiosulphate meant that more time was required for the solution to become cloudy and for the Sulphur to form. Rate of Reaction 100/time (s -1) Relative Concentration of Sodium Thiosulphate (mol/l) 0.5 1 1.6 2 2.3 3 3.3 4 4.9 5 7 ...read more.

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