Rates of reaction - kinetics (A2)
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I’ve been given the coursework of working out the orders of reaction between Na2S2O3 and HCl in the presence of water. That's fine, but how do I justify the volumes used? We've been given set concentrations of 0.4M for Na2S2O3 and 2.0
for HCl, but I don’t know how to justify how much is used of each nor the total volume.
Ulex writes
You notice that the HCl concentration is high relative to the thiosulphate concentration. In the first set of experiments (to find the order with respect to thiosulphate) you therefore need to keep the acid concentration constant and vary the initial concentration of thiosulphate.
Aim to mix equal volumes of the two solutions (this makes the arithmetic easier). If you are going to use a boiling tube (150 x 25 mm) , use 10 cm3 of each.
In the first experiment use the two solutions given. In the second use 10 of acid and 9 of thiosulphate + 1 of water (10 altogether), next, use 8 thio + 2 water and so on. If you are going to use some other apparatus, make the total volume greater or lass to match. Don’t forget the subtle point that when you mix equal volumes of two solutions, you effectively halve the concentration of both of them!
In the second set of experiments you keep the thiosulphate constant and of (relatively) high concentration and vary the concentration of the acid.
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updated: 17 December 2003
