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# Determining the Rate Equation of a Reaction

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Introduction

Determining the Rate Equation of a Reaction Plan The aim of this experiment is to determine the rate equation for the reaction between sodium thiosulphate and hydrochloric acid using the order of the reaction with respect to each of the reagents. HCl (aq) + Na2S2O3 (aq) --> 2NaCl (aq) + SO2 (g) + S (s) When Hydrochloric acid is added to sodium thiosulphate, a solid ppt of sulphur is formed. I will use this to judge when the reaction has ended. The rate equation for this reaction is R = k [HCl]x [Na2S2O3]y In this equation: R = the rate of reaction k = the rate constant x and y = order of reaction with respect to HCl and Na2S2O3 (e.g. 0, 1, 2 etc...) [HCl] = the concentration of HCl [Na2S2O3] = the concentration of Na2S2O3 My experiment will enable me to calculate x and y through plotting the volume against the reciprocal of the time it takes for the ppt to form. Preliminary work: The demonstration done by my teacher show that 50 cm3 of thiosulphate and 20 cm3 of deionised water mixed with 5cm3 of hydrochloric acid took 14.93 seconds to form the ppt. ...read more.

Middle

* One 250 cm3 conical flask into which I will mix my reagents * Two funnels to full my burettes, which I will remove before looking at the meniscus. * I will be supplied with deionised water, HCl and Na2S2O3 Concentrations: Run 1 Run 2 Run 3 Run 4 Run 5 Na2S2O3 (cm3) 50 45 40 35 30 Deionised Water (cm3) 20 35 30 35 40 Variables: Fixed Independent Dependent Temperature: the experiment will be done at room temperature. I will control the temperature because changing the temperature changes the rate which will affect me results. Concentration of HCl: I will keep this constant because I can only change the concentration of one reagent to see the effect this has on the rate. If I change both reagents I will not be able to tell the order of the reaction is with respect to which reagent. The white tile and cross: changing this might affect my visibility of the cross and the time. Total volume: I will keep this the same to ensure a fair experiment and the same visibility due to smaller volumes being more shallow and I might see the ppt at different times. ...read more.

Conclusion

this will go along my y-axis. The volume of the sodium thiosulphate will go along the x-axis. Based on the shape of my graph I will then decide what the order of the reaction is with respect to the sodium thiosulphate. Safety: Chemical Hazards HCl Solutions equal to or stronger than 2 mol dm-3 but weaker than 6.5 mol dm-3 are IRRITANT. Na2S2O3 Sodium thiosulphate may be harmful if you swallow it. It may also irritate the eyes or lungs. Eye contact: Flush the eye with plenty of water. If irritation persists, call for medical help. Skin contact: Wash off with water. If swallowed: If the amount swallowed is not trivial, call for medical help. SO2 Major hazard : Inhalation Odour : Pungent and Irritating S Contact with the eyes can cause irritation. The solid may also irritate the lungs if breathed in. Sulphur burns to give toxic gases, so should not be burnt in the open laboratory. Wear safety glasses. Solid sulphur should pose only minor hazards unless heated to a temperature at which it will burn. Safety glasses required. NaCl May cause eye irritation. Reference: http://www.cartage.org.lb/en/themes/sciences/Chemistry/Miscellenous/Helpfile/Kinetics/Rateorder.htm Chemistry 2 Cambridge Advanced Sciences Endorsed by OCR page 109 http://physchem.ox.ac.uk/~hmc/hsci/chemicals/sodium_thiosulphate.html ?? ?? ?? ?? Chemistry Plan Alota boka ...read more.

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