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  • Level: GCSE
  • Subject: Science
  • Document length: 3491 words

Measuring the reaction rate of sodium thiosulphate in hydrochloric acid

Extracts from this document...

Introduction

G.C.S.E. Chemistry Investigation - Reaction Rate of Sodium Thiosulfate in Hydrochloric Acid Contents Page 1. Aim.............................................................................................................. 3 2. Introduction................................................................................................. 3 2.1 Rate of reaction 2.2 Collision theory 2.3 Activation energy 2.4 Factors 3. Preliminary work......................................................................................... 5 3.1 Summary 3.2 Concentration or temperature 3.3 Equipment 4. Method........................................................................................................ 6 4.1 Equipment 4.2 Diagram 4.3 Procedure 4.4 Fair test 4.5 Safety precautions 5. Results........................................................................................................ 8 5.1 Tables 5.1.1 Preliminary experiments 5.1.2 Final experiment 5.2 Graphs 5.2.1 Preliminary experiments 5.2.2 Final experiment 6. Analysis..................................................................................................... 12 7. Conclusion................................................................................................ 12 8. Evaluation................................................................................................. 12 9. Bibliography.............................................................................................. 13 1. AIM Our task was to investigate the factors affecting reaction rate and the effect of varying one of these factors on the rate of the chemical reaction between sodium thiosulfate (Na2S2O3) and dilute hydrochloric acid (HCl). Na2S2O3 (aq) + 2HCl (aq) 2NaCl (aq) + H2O (l) + S (s) + SO2 (g) sodium thiosulfate + hydrochloric acid sodium chloride + water + sulfur + sulphur dioxide 2. INTRODUCTION 2.1 Rate of Reaction The rate of reaction is intuitively defined as the average speed at which the substances in a reaction interact to cause a chemical or physical change. The rate of reaction can either be measured by the rate at which a reactant is used up or the rate at which a product is formed. The method chosen depends on the reaction being studied, but in our case it was more convenient to measure the rate at which the products of the reaction were formed. Different reactions occur at different rates. For example, the oxidation of iron in the atmosphere is a very slow reaction and can take many years: it has a low rate of reaction. Meanwhile, the combustion of butane in a fire is a much quicker reaction and takes place within a fraction of a second: it has a high rate of reaction. Figure 1: Figure 2: There are five main factors which affect the rate of a reaction; the concentration of reactants in solution, the temperature of reactants, the pressure in gases, the surface area of reacting solids and the use of a catalyst. ...read more.

Middle

We conducted our experiment based on what we learned from our preliminary work. The equipment was set up as shown in the equipment diagram, with the water bath running at target temperature. Firstly, we would remove the chemicals from the water bath simultaneously and pour 30ml of each into their respective measuring cylinders using funnels, checking that we had exactly 30ml of each chemical before pouring them into the conical flask together, swirling it five times clockwise and finally setting it down. We would use the stopwatch to time from when the flask was set down to when the 'X' disappeared from view. Figure 7 shows the side and top view of the flask during this phase. 4.4 Fair test If our investigation was to be successful we needed to make sure that we were not corrupting our results in any way. Therefore, while we tested the effect of a particular parameter on the rate of reaction between sodium thiosulfate and hydrochloric acid we ensured that all other factors remained constant. For example, when we were testing the effect of temperature, we used a constant 1.0M concentration of acid. Similarly, when we were testing for concentration, we used room temperature as a constant because it would not have to be monitored. There were also simple things that needed to be considered, such as using the same amounts of all chemicals and taking repeat measurements in order to plot averages on graphs. We also used separate funnels and measuring cylinders for each chemical so that the sodium thiosulfate and hydrochloric acid would not become contaminated. Another problem with sodium thiosulfate is that it reacts with oxygen in the air, meaning that we had to keep it sealed until the last minute and then carry out the experiment as quickly as possible. Finally, when carrying out the experiments at the higher temperatures, the water bath was set to heat the chemicals to a few degrees above the target temperature to account for the fact that they would lose some heat when we took them out. ...read more.

Conclusion

This is because Graph 3 shows a low scatter of data around the line of best fit but has high range bars. Despite the effort that we went through to ensure that we achieved reliable results, there are a number of signs that the experiment did not go as well as we hoped. For example, we have a number of anomalies in our data where the results do not follow the trend. We think that some are down to human error misinterpreting when the tile marked with an 'X' disappeared from view while others are due to environmental temperature changes in the classroom affecting our chemicals.. Our range bars are also greater than we had hoped. Graphs 1 and 3 in particular showed an interesting trend, that the range bars grew as the temperature decreased. To improve on this I could get a better method for measuring when the 'X' has disappeared other than just by human eye, as on one occasion (table 4, series 1, 4°C), we disagreed about when it was no longer visible. Nevertheless, our averages plot very close to the line of best fit on our graphs, so we can assume that any uncertainty in the results is due to human error. To improve the accuracy and reliability of our results, I would replace the technique of deciding when the tile marked with an 'X' had disappeared by visual evaluation with a laser and a sensor. When the solution becomes opaque, the sensor will no longer detect the laser and will subsequently stop the electronic time. This would reduce the variation in the data. Another suggestion for improvement would be to take more repeat experiments. This improves the accuracy of the average, which is plotted on the graphs. We had already increased the number of repeats to six after completing our preliminary experiments but taking more would improve the accuracy further. If the necessary equipment was supplied to us, it would be possible to achieve results that we could have almost complete confidence in. 9. ...read more.

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