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Question

25mL of 0.50 M H2O2 solution is added to 50 mL of 0.20 M KMnO4 in acid solution. Which of the following statements are true?

A
0.010 mole of oxygen is liberated
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B
0.030 g atom of oxygen gas is evolved
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C
0.005 mole of KMnO4 is left
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D
0.0025 mole of H2O2 does not react with KMnO4
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Solution

The correct option is C 0.005 mole of KMnO4 is left
Finding the limiting reagent

The reaction involved is:

KMnO4+H2O2Mn2++H2O+O2

The balanced reaction is:

2KMnO4+5 H2O2 5O2+2MnO+2KOH+4H2O

Moles of KMnO4 taken

= Molarity × Volume (in L)

=0.20×501000=0.01 mol

Moles of H2O2 taken

=Molarity×Volume (in L)

0.50×251000

0.0125

From the balanced chemical equation, 2 mol of KMnO4 reacts with 5 mol of H2O2.

1 mol of KMnO4 reacts with 2.5 mol of H2O2. 0.01 mol of KMnO4 will react with 0.025 mol of H2O2.

But the total moles of H2O2 present is 0.0125.

Hence, H2O2 is the limiting reagent.

Analysing the option

Option (A):

5 mol of H2O2 produces 5 mol of O2
Therefore, 0.0125 mol of H2O2 will produce 0.0125 mol of O2.

Option (B):

5 mol of H2O2 react with 2 mol of KMnO4

1mol of H2O2 react with 25 mol of KMnO4

0.0125 moles of H2O2 will react with 0.005 moles of KMn04.

So, the moles of KMnO4 left

=0.010.005=0.005 mol

Option (C):

Moles of oxygen evolved =0.0125 mol
Mass of oxygen evolved = Number of moles × Molar mass

=0.0125 mol×32 g mol1=0.4 g

Option (D):

Since H2O2 is the limiting reagent, so all of H2O2 reacts.

So, option (B) is the correct answer.

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