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How does changing the Concentration of Sodium thiosulphate affect how fast it reacts with an acid?

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How does changing the Concentration of Sodium thiosulphate affect how fast it reacts with an acid? Introduction: The purpose of this investigation is to determine, how the rate of the reaction changes when sodium thiosulphate [Na2S2O3] is mixed with hydrochloric acid [HCl] at different concentration. Prediction: The collision theory states that, the higher the concentration and if the volume of a solution stays constant; then the probability of collisions within the solution between particles will be higher than a lower concentrated solution with the same volume. The amount of particles in a concentrated solution will be greater so therefore, the probability of collisions occurring will be greater. In addition, the probability of successful collisions also increases proportionally if the concentration is increased at the same rate. E.g. Therefore, after considering collision theory involving the concentration of substances I can predict that the rate of the reaction between sodium thiosulphate [Na2S2O3] and hydrochloric acid [HCl] will increase proportionally as the concentration of sodium thiosulphate [Na2S2O3] increases. So, the higher the concentration, the shorter amount of time will be required for the cross to disappear. This happens because, the equation: Na2S2O3 + 2HCl " 2NaCl + SO2 + S + H2O, the sulphur causes the conical flask to become cloudy. However, there are other aspects involving collision theory like; temperature and catalysts, temperature is involved but is not being altered so therefore, will not alter the rate of the reaction, a catalyst is not being administrated so therefore, it will not assist in increasing the rate of the reaction. ...read more.


3. The person who watches the cross must operate stop clock because, it will be a quicker reaction time and create less accurate times. If some one were to be told to stop the clock then the reaction time would be slower and affect accuracy. 4. Distilled water must be used at all times, not tap water because, tab water has impurities within it, and these impurities may affect the rate of reaction and would create inaccuracies within my results. 5. Also, the same cross must be used all the way through the experiment because, other crosses may be of different thickness and shade so the cross may appear to disappear faster or slower in comparison to my other results. Equipment: * Sodium thiosulphate [Na2S2O3] 3x175cm3 * Hydrochloric Acid [HCl] [1Molarity solution] 3x25cm3 * Distilled Water 3x75cm3 * Conical Flask x1 * Measuring Cylinder x1 * Paper and Pen x1 Method: * Draw a cross on the paper using the pen. [To be done once only] * Place it under the conical flask. * Measure 45cm3 of sodium thiosulphate [Na2S2O3] using the measuring cylinder and place in the conical flask. * Measure 5cm3 of distilled water using the measuring cylinder and place in the conical flask. * Measure 5cm3 of hydrochloric acid [HCl] using the measuring cylinder and place in the conical flask. [Giving a total of 55cm3 always] * As soon as the previous process has been completed activate the stopwatch immediately. ...read more.


So if this investigation were to be repeated, I would keep my chemicals in a water bath so that the chemicals would definitely be at the same temperature before adding them to the conical flask. Swirling the solution is a good method of starting the reaction off but it was difficult to create the same swirling motion each time an experiment was set up. Keeping the cross dry was also difficult; the ink started to run and it was difficult to judge when to stop the stop clock. If the experiment were to be repeated it would be a good idea to laminate the cross, then it could be wiped free of liquid after each experiment. Considering that the anomalous result was not far off the line of best fit and all other points fit the line of best fit well so that I am able to conclude, the results that have been recorded should give enough evidence in order to support my conclusions. Further experiments could be planned in order to research how temperature affects the rate of a reaction, the molarity and volume of sodium thiosulphate [Na2S2O3] and hydrochloric acid [HCl] because, that would give an equal probability of particles colliding. The temperature of sodium thiosulphate [Na2S2O3] would be varied at regular intervals before the acid was added at each varied temperature. Results would be recorded and graphs drawn accordingly. Finally, conclusions and evaluations would be considered in order for other experiments to be planned and researched. Fred 11NW - 111Y Chemistry ...read more.

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