- #1
Titan97
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Homework Statement
To a 25ml H2O2 solution, excess acidified solution of potassium iodide is added. The libereated iodine required 20ml of 0.3N sodium thiosulphate solution. Calculate the volume strength of H2O2.
Homework Equations
Normality = n-factor × Molarity
Volume strength = Molarity × 11.2
The Attempt at a Solution
I will use moles and not equivalence. But to do that, I need to convert normality to molarity.
For the reaction of sodium thiosulphate with iodine, n-factor is 2 for sodium thiosulphate.
Hence M = N/n = 0.15.
So number of milli moles of thiosulphate is 3.
$$I_2 + 2Na_2S_2O_3 \rightarrow 2Na_2S_4O_6 + 2NaI$$
So number of millimoles of iodine is ##\frac{3}{2}##.
$$2H^+ + H_2O_2 + 2KI \rightarrow 2H_2O+I_2+2K^+$$
Hence millimoles of hydrogen peroxide is ##\frac{3}{2}##
So molarity of hydrogen peroxide is ##\frac{3}{50}##
So volume strength = ##\text{M}\times 11.2 = 0.672##
But the answer given is double of what I got.