Rates of reaction - kinetics (A2)
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I am investigating the rate of reaction between potassium manganate(VII) (from 0.005 to 0.001 M) and oxalic acid (0.05 to 0.01 M). When adding it to the colorimeter, do I add a ratio of 1:1 and how would I measure this out... burette, pipette filler?
220908
Corrie writes .....
I would use burettes or pipettes to measure the out the solutions, depending on the total volume of the reaction mixture you require - probably 10 cm3 in total will be enough to fill a 1 cm colorimeter cell. There is no requirement to mix the solutions in a 1:1 ratio, but it makes it easier to work out the actual concentration of each substance in the mixture. Presumably you will do a series of experiments with a fixed concentration of potassium manganate(VII) and varying concentrations of oxalic acid, and vice versa, in order to find out the effect of these two substances on the rate - and hence deduce the orders?
One problem that arises when using colorimetry to study reactions involving manganate(VII) ions is their intense colour. You must use concentrations of potassium manganate(VII) (and an appropriate filter or wavelength setting - depending on what type of colorimeter you have) in the reaction mixture that have an absorbance of about 1 (i.e. 10% transmission) in a 1 cm colorimeter cell. If the potassium manganate(VII) is too concentrated, all the light will be absorbed and you will see no change until sufficient reaction has occurred to reduce the absorbance value to below 2. However, if the concentration of potassium manganate (VII) is very low then the reaction will be very slow. A further warning: this reaction is very slow (initially) at room temperature unless a catalyst is present.
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updated: 23 September 2008
