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# ... Watch

1. nm
2. The concentration remains the same, there's just less of it.
3. (Original post by bzzz)
I’m writing up the method for an experiment I’m doing where I measure the rate of decomposition of hydrogen peroxide using different catalysts, different concentrations of peroxide/catalyst etc etc.

The first thing I want to do is to prepare different concentrations of peroxide by dilution – I think the most concentrated I’m going to get is 5 volume or something (this means 1 volume of peroxide produces 5 volumes of oxygen). This translates to a certain concentration in terms of moldm-3, but I don’t think it’s a very even number. I want to use about 8 different concentrations, so should I dilute it using the volume measurement of concentration (4.5, 4, 3.5…) or dilute the 5 volume peroxide to a nice number of moles, and then dilute from there?

Another thing I want to do is measure the order of the catalysed reaction with respect to peroxide. I want to plot graphs of

a) the volume of peroxide against time,
b) the concentration of hydrogen peroxide against time (the gradients of different tangents will, I think, give me the reaction rate at each time), and
c) the reaction rate against the concentration.

For a), I’m going to use a burette to measure the volume of oxygen produced at set times. I was originally going to use this to calculate the moles of hydrogen peroxide (convert volume of oxygen -> moles of oxygen -> moles of peroxide) and then convert that to the volume of peroxide. I need to use the formula moles = concentration x volume, but as the hydrogen peroxide decomposes, won’t the concentration change? I don’t know how to get the concentration.

I could also use the initial concentration (e.g. 5 volume) – if I start out with 20cm3 of peroxide and get 10cm3 of oxygen at a certain time, I’ll know 2cm3 hydrogen peroxide has been used up, so perhaps there’s 18cm3 left? Does the concentration change?

if anyone could shed some light on this it would be great...
The hydrogen peroxide you are using is a solution in water. As it reacts the concentration decreases, but the volume remains the same.
4. (Original post by bzzz)
Won't some of it be lost as oxygen?
Such a tiny amount as to be absolutely insignificant

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Updated: December 29, 2010
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