The determining of a rate equation from the reaction of sodium thiosulphate with hydrochloric acid - page 1
Keywords: The determining of a rate equation from the reaction of sodium thiosulphate with hydrochloric acid
By Carlitob10 on 04/11/2006 11:57:07
Level: A Level (Year 13)
Page Number: 1 of 8 pages: 1 2 3 4 5 6 7 8
The determining of a rate equation from the reaction of sodium thiosulphate with hydrochloric acid
Planning
Background knowledge
Sodium thiosulphate and hydrochloric acid react according to the stoichiometric equation
2HCl (aq) + Na2S2O3 (aq) 2NaCl (aq) + SO2 (g) + S (s) + H2O (l)
The rate equation in respect to the reaction in this experiment is in the form:
Rate = k [Na2S2O3]s [HCl]t
Where k is the rate constant, s is the order of reaction with respect to sodium thiosulphate and t is the order of reaction with respect to hydrochloric acid.
I will be determining the order of reaction for each reactant by varying the concentration of each species in turn, keeping the others constant.
The reaction can be followed using the precipitated sulphur which causes the solution to become opaque. The rate can be determined by measuring the time taken for an ‘X’ drawn on a tile and placed under the reaction vessel to become obscured.
Collision Theory:
The rate at which a reaction occurs depends on three factors
1. How frequently do reactions collision occur
2. What fraction of the collisions have sufficient energy for the reaction to occur
3. What fractions of the reactions have the correct orientation for the reaction to occur
Increasing the concentration of the reactants often increases the rate of the reaction by increasing the frequency at which collisions occur
For a chemical reaction, we often determine the order with respect to a reagent by determining the initial rate. When more than one reactant is involved, we vary the concentrations in a systematic way so that the effect of concentration of one of the reactants can be measured. This, in broad terms, is what I will be doing in this series of experiments.
Preliminary Work
Prior to my investigation, my teacher performed a trial run of the experiment where he mixed together 50 cm3 of sodium thiosulphate (0.4 mol dm-3) with 5.0 cm3 of hydrochloric acid (2.0 mol dm-3) diluted with 20 cm3 of water in a conical flask. This was placed on a tile marked with an ‘X’ so the time for production of sulphur could be timed using a stopwatch. The time it took for the ‘X’ to disappear was timed at 15.86 seconds.
Concentrations of reagents
As I am studying the effect of concentration on the reaction between
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