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Investigation of Factors Effecting Reaction Rates

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Introduction

Investigation of Factors Effecting Reaction Rates Sodium thiosulphate + Hydrochloric acid ? Sulphur dioxide + Water + Sodium chloride Na2S2O3 + 2HCl ? 4SO2 + 2H2O + 6NaCl The sulphur is produced slowly as a pale yellow precipitate and makes the reaction mixture cloudy. The speed of the reaction may be found by finding the time taken to to reach a particular level of cloudiness of the reaction mixture. There are factors which can affect the speed of the reaction, including * temperature * catalyst * surface area * concentration I am going to investigate the effect of the concentration of thiosulphate on the speed of the reaction. Preliminary Work I have carried out a preliminary experiment to help me plan out this investigation. I used a 25cm3 measuring cylinder to measure out 25cm3 of sodium thiosulphate. This is because if I had used a 10cm3 measuring cylinder, I would have had to measure out the sodium thiosulphate three times. This would not be very accurate because every time I pour out the liquid some is still left in the cylinder. I did not use a bigger cylinder than 25cm3 because that would not be accurate either to measure a small amount. The concentration of the sodium thiosulphate was 40g/dm3. It is not worth using a pipette to measure out the sodium thiosulphate because all the effort needed to use it is not worth the accuracy it will give because such accuracy is not needed. ...read more.

Middle

I will use the same cross and start the stopwatch every time when all the hydrochloric acid is poured in. I will try to do the experiment on the same day so that the temperature is constant. I will carry out the experiment for each concentration three times to get an average. In this way my results will be more reliable. I will measure out the liquids as accurately as possible. Safety I will wear goggles and overall to protect eyes and clothing. I will keep the room well ventilated so that I will not breath in a lot of sulphur dioxide. I will throw away the sodium chloride solution as soon as I have finished the experiment so that I will not breath in a lot of the sulphur dioxide. Concentration I will use five different concentrations of sodium thiosulphate. The highest concentration is 40g/dm3. I will use concentrations of 8g/dm3, 16g/dm3, 24g/dm3, 32g/dm3 and 40g/dm3. After I have obtained results for these, if I do not find a pattern, I will make up other concentrations and carry out the experiment on them until I find a pattern in my results. To make up the concentrations I want, I need to do the following calculation: total volume x concentration wanted = volume needed in concentration given measuring cylinder I will be given sodium thiosulphate of concentration 40g/dm3. To make up sodium thiosulphate of 8g/dm3 concentration, the calculation would be, 25cm3 x 8g/dm3 = 5cm3 of sodium thiosulphate 40g/dm3 I need to add 5cm3 of sodium thiosulphate of concentration 40g/dm3, with 20cm3 of distilled water, to get 25cm3 of sodium thiosulphate of concentration 8g/dm3. ...read more.

Conclusion

According to my graph, sodium thiosulphate of concentration 15g/dm3 has a reaction rate of 0.014s-1. Sodium thiosulphate of concentration 30g/dm3 has a reaction rate of 0.028s-1. Since the reaction rate doubles as the concentration doubles, the graph supports my prediction. I have got two anomalous results. For 8 g/dm3, I measured a time of 244.83s. For 16g/dm3, I measured a time of 81.64s. I have not included them in my average. These could have been anomalous results because I did not measure the hydrochloric acid or the sodium thiosulphate as accurately as possible. I might have been distracted and not seen that the cross had already disappeared, so I might have stopped the stopwatch a long time after the cross had disappeared. There might have been a temperature change as I was taking those two results, possible because someone was opening or closing a door or a window. I'm not that sure my results are accurate and someone else would get the same results as me since there are many errors and mistakes I could have made. I also need to conduct this experiment with at least ten different concentrations and repeat them at least five times to be certain that my results are correct and someone else would get the same results. The two anomalous results show that this experiment is not very accurate. To get better results, the cross needs to be laminated as it got wet and smudged, which would have affected the results as the visibility of the cross would have decreased. Further work is needed to confirm my results as I have already explained. ...read more.

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