How to calculate the number of moles of hydrogen peroxide that has reacted? I be

Question

How to calculate the number of moles of hydrogen peroxide that has reacted?

I believe the reaction is H2O2 +2S2O3 -2 + 2H+ -> S4O6 -2 +H2O

Calculate the change in concentration of hydrogen peroxide in each case, i.e., moles of H2O2 reacted per litre of solution.  Hint:   Recall the total volume, and you have calculated the number of moles that reacted, previously

Calculate the rate of the reaction?

The following chart will be helpful as a checklist for the preparation of the solutions which will be used in this experiment: Use pipettes to measure the buffer, Na2S203 and the H202 solutions. Use a burette to measure the KI solution and a graduated cylinder for the distilled water. Use the graduated dropper provided to measure the starch. 0.0200 0.1 M Distilled stilledbuffer 0.300 M starch H202 sol'n H2o mL 164.5 162 158 148 128 (mL) KI (mL) (mL)Na,s,O, (mL) Na2S20; (mL) 10 10 10 10 10 10 10 10 20 40 3.5 10 10 10 10 10 Note that the total volume in each case is 200 mL.

Explanation / Answer

The reaction will be

Na2S2O3(aq) + 4H2O2(aq) Na2SO4(aq) + H2SO4(aq) + 3H2O(l)

So as per the stoichiometry 1 mole of Na2S2O3 will react with 4 moles of H2O2

Moles of  Na2S2O3   molarity X volume = 0.02 X 10 = .2 millimoles

Moles of H2O2 present = 0.1X 10 = 1 millimoles

So moles of H2O2 react will be: 4 X .2 millimoles = 0.8 millimoles

So change in concentration = 1-0.8 / volume = 0.2 / 200 = 0.001 M

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