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What Affects the Rate of Reaction Between Sodium Thiosulphate and Hydrochloric Acid?

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Introduction

What Affects the Rate of Reaction Between Sodium Thiosulphate and Hydrochloric Acid? By Will Lilley 14-3-10 What affects the rate of reaction between Sodium Thiosulphate and Hydrochloric acid? By Will Lilley Aim I plan to find out how the rate of reaction between Sodium Thiosulphate and Hydrochloric acid can be sped up or slowed down depending on the concentrations. Introduction To know what affects the rate of reaction in an experiment, we must first know how to calculate the rate of reaction. This is done by dividing 1 by the amount of time taken for the reaction to have completed. The rate of reaction is driven by the collision theory, which states that "When two chemicals react, their molecules have to collide with each other with sufficient energy for the reaction to take place." http://www.purchon.com/chemistry/rates.htm There are also four factors which could affect the rate of a reaction, according the collision theory: Temperature, concentration (of the solution), pressure (in gases), and the surface area of the solid reactants. By the end of the experiment, I hope to have proved that when the concentration of the solution is increased, the rate of reaction increases, because there are more molecular collisions. I am going to measure the rate of reaction that occurs when I mix sodium thiosulphate and hydrochloric acid. A product of this reaction will be sulphur in the solution, which will make it go cloudy. This is shown by: Sodium Thiosulphate + Hydrochloric acid �Sodium Chloride + Water + Sulphur Dioxide + Sulphur Na2S2O3 (aq) + 2HCl (aq) � 2NaCl (aq) + H2O (l) + SO2 (g) + S (s) ...read more.

Middle

I drew a thick black cross on a piece of paper. I then created a reaction table, seen below, which I could follow as I was performing the experiments. I placed these amounts into a conical flask (which was placed on the cross) and used a stopwatch to record how long it took for the reaction to turn to a cloudy white colour. When I could no longer see the cross, I stopped the stopwatch and recorded how long it had taken for the reaction to take place. Once this had been done, I washed the beaker out and started again with the next amount. It is possible that my measuring of the liquids could have been more accurate, and there may have been some time lapse problems using the stopwatch. Measuring the liquid using pipettes may have been more consistently accurate. Results Here is my table of results from the experiments. It involves the three experiments that we did, along with the average time and the average rate of reactions: If we look at the average time (in seconds) column, we can see that each experiment's reaction time gradually decreases. However, as we can see from the table, there is an evident outlier between the times gathered from the 25cm3 (of thiosulphate) experiment and the 30cm3 experiment (51.67 value). This can also be seen on my graph, as the 30cm3 experiment does not fit into the line of best fit. On my graph (appendix 1) I have plotted the average rates of reaction and used the rates for the upper and lower time values to calculate other rates. These can be seen in the table below. I have used these calculations to build error bars into my graph. ...read more.

Conclusion

There are several reasons for this; A pattern was clear from my graph (an upward sloping straight line suggesting a strong positive correlation between volume and rate of reaction) and from the table of figures even with outlying values. We would need to repeat the experiments again several more times to improve reliability but if my theories in section (B) above are correct, then the overall conclusion would seem to be sound. With more time I should also like to have done an experiment where I varied the volumes of acid and kept the thiosulphate constant to cross-check the results and ensure reliability. The graph suggests that a fair degree of reliability in my results. My line of best fit passes within the error bars of most of the points plotted. According to the table in my results section, the average reaction time falls steadily with an increase of thiosulphate and the average rate of reaction increases with increased levels of thiosulphate. This suggests that the results have an acceptable level of accuracy and thus the conclusion is reliable. I have tried to investigate my conclusion in more detail by calculating the gradient of my line of best fit. Using my knowledge that the equation of a straight line graph can be expressed as 'y=mx+c', I can show that the equation of my line is 'y=0.088 x - 0.26'. Therefore, the expectation that rates of reaction would double with twice the volume of thiosulphate was inaccurate. However, this equation does give me the ability to forecast the reaction for any given volume of thiosulphate. To improve the reliability of my conclusion I could redo the experiments and make predictions about the rates of reaction using my graph. If my predictions were correct, this would show that my conclusions were correct. ?? ?? ?? ?? ...read more.

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