Question

1 5 mL of 3% H2O2 & 10 mL of 0.60M KI

5 mL of 3% H2O2 & 10 mL of 0.30M KI

5 mL of 2.25% H2O2 & 10 mL of 0.60 M KI

What is the Concentration of H2O2 in each one?

Answer 1

Calculate the strength , and Molarity of 3% H2O2

Since 3% H2O2 means 10 volumes of H2O2, so 1 litre of H2O2 will give 10L of oxygen at STP

2H2O2(l)------------> O2(g) + 2H2O(l)

2 x34=68g...................22.4 L at STP

Thus 22.4 L of O2 is produced from H2O2 = 68 g

therefore 10 L---------------------------------------={ (68 x 10 ) /22.4 } g.

.............................................................. ........= 30.36 g / L

Hence , strength of H2O2 in 3% H2O2 is 30.36 g / L

& Molarity of 3% H2O2 = ( 30.36 / 34 ) = 0.8929 M

Now 15 ml this solution ie 0.8929M H2O2 is mixed with 10ml of 0.6M KI

Apply the relation M_H2O2 x V_H2O2  = M_KI  x V_KI ,to find out equivalence in volume of H2O2

0.8929 x V_H2O2   = 0.6 x 10

..................V_H2O2 = 6.72 ml

Thus , 6.72 ml of 0.8929M H2O2 is used up in the reaction with 10 ml of 0.6M KI solution,

volume of unused 0.8929 H2O2 present in 25 ml of reaction mixture = (15 -6.72 ) = 8.28 ml

So, Molarity of H2O2 in solution = (8.28 x 0.8929) /25

.....................................................= 0.2957M

Similarly, for Case II concentration of H2O2 can also be calculated to get-

Concentration of H2O2 when 5ml of 3%H2O2 is mixed with 10 ml of 0.3M KI solution = 0.0976M

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The third question can also be solved the same way , after calculating the moarity of 2.25% H2O2.

However,glad to help .

Please post the third question separately as fresh question for detailed work outs.