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rates of reaction

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Introduction

Calculating Reaction Rate Between Sodium Thiosulphate and Hydrochloric Acid Coursework In this experiment I will be seeing how the concentration of Sodium Thiosulphate, Na2S2O3, and Hydrochloric Acid, HCl, affects the rate of the reaction. In this reaction the solution turns milky yellow as sulphate is displaced and forms a solid precipitate. Na2S2O3 (aq) + 2HCl (aq) ----------> 2NaCl (aq) + H2O (l) + SO2 (aq) + S (s) The Rate of a reaction can be represented as: ?concentration and so is the time ? time taken for the reactants to be used up. Therefore I will be investigating if either: Rate ? [Na2S2O3]x or/and Rate ? [HCL]Y where X and Y are the orders of the reaction. To calculate the rate equation and orders of the reaction I am going to use the log function: As Rate ? [Na2S2O3]x and Rate ? [HCL]Y Rate = k1 � [Na2S2O3]x Rate = k2 � [HCl]Y Take logs logRate = logk1 + X log[Na2S2O3] logRate = logk2 + Y log[HCl] eq. of line Y = C + M X Y = C + M X This shows how the power, and order of the reaction, can be found by drawing a graph of logRate against log[concentration] and the gradient of the line will give the order of the reaction. ...read more.

Middle

8. Secondly replace the Sodium Thiosulphate with the HCl and copy above steps by measuring out correct concentrations and place into 5 more 50cm3 beakers. 9. This time add 25cm3 of Na2S2O3 into the bottom of the conical flask before recording the time taken for the cross to disappear again, for all the concentrations. 10. Repeat all results again for HCl concentrations. Initial Rates can then be calculated. Dilution Tables Na2S2O3 Concentration / moldm-3 Na2S2O3 (1M) / cm3 Distilled Water / cm3 1.0 20 0 0.8 16 4 0.6 12 8 0.4 8 12 0.2 4 16 HCl Concentration / moldm-3 HCl (2M) / cm3 Distilled Water / cm3 2.0 20 0 1.6 16 4 1.2 12 8 0.8 8 12 0.4 4 16 Safety Points As concentrated Hydrochloric acid will be used make sure eye and hand protection is worn. In case of contact, immediately flush skin with plenty of water for at least 15 minutes and with eye contact get medical attention immediately. Sulphur is also present so make sure the room is well ventilated to allow fumes to escape. Take care with glass wear, such as pipettes as they are fragile and may break easily. ...read more.

Conclusion

When the temperature increases the k constant will increase, this is because the molecules have more kinetic energy and there is a higher probability that they will collide and react. This means its is hard to control this factor which is affecting the rate of the reaction. There are also many accuracy errors caused by percentage error in measuring. There is a time error in the time taken when the cross disappears and the delay in stopping the time. When using the graduated there was an error of 0.05/20 = 0.25% error, human reaction time is about 0.2/9.34 = 2.1%. To reduce this error I would choose another method of measuring the rate. Instead of using the cross method I would use a light intensity machine that could measure the change in colour over a period of time and stop and start timing when it had reach a certain value. This quantitative method of measuring should make the results more accurate. To control the temperature I could use a large water bath which could control the temperature throughout the reaction. Another method that could be used is to measure the products formed. The easiest would be using a gas syringe to measure the amount of SO2 formed. This again would give a more quantitative results and increase the accuracy and reliability. ...read more.

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