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Question

What volume of 0.10 𝑀 H2SO4 must be added to 50 𝑚𝐿 of a 0.10 𝑀 𝑁𝑎𝑂𝐻 solution to make a solution in which the molarity of H2SO4 is 0.050 𝑀?
  1. 50 mL
  2. 400 mL
  3. 150 mL
  4. 100 mL

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Solution

The correct option is D 100 mL
The reaction of H2SO4 reacting with 𝑁𝑎𝑂𝐻 is as follows:
H2SO4+2NaOHNa2SO4+2H2O

For a neutralization reaction,
Milliequivalents of 𝑁𝑎𝑂𝐻 = Milliequivalents of
H2SO4
Volume of 𝑁𝑎𝑂𝐻 × Normality of 𝑁𝑎𝑂𝐻
= Volume of H2SO4 × Normality of H2SO4
We know that,
Normality=Molarity×nfactor

Volume of 𝑁𝑎𝑂𝐻 × Molarity of 𝑁𝑎𝑂𝐻 ×
𝑛 − 𝑓𝑎𝑐𝑡𝑜𝑟 = Volume of H2SO4 × Molarity of
H2SO4×nfactor
50 mL×0.1M×1=y mL×0.1M×2
y=25 ml

So, for complete reaction with 50 𝑚𝐿 𝑜𝑓 0.10 𝑀 𝑁𝑎𝑂𝐻, 25 𝑚𝐿 of 0.1 𝑀 H2SO4 is required.

Thus, the total volume of the solution after neutralization will be 50 𝑚𝐿 +25𝑚𝐿 = 75 𝑚L
To obtain 0.05 𝑀 H2SO4 , more volume of 0.10 𝑀 H2SO4 must be added.
Suppose the volume of 0.1 𝑀 H2SO4 to be added to this solution to make the molarity of sulphuric acid equal to 0.05 𝑀, is 𝑥 𝑚𝐿,
Then,
𝑉1 = Extra volume of H2SO4 needed = 𝑥 𝑚𝐿
𝑀1 = Molarity of H2SO4 = 0.10 𝑀
𝑉2 = Total volume of the resultant solution
after adding extra H2SO4 = (75 + 𝑥) 𝑚𝐿
𝑀2 = Molarity of the resultant solution
= 0.05 𝑀

We know that M1V1=M2V2
x×0.10M=(75+x)×0.05 M
0.10x=3.75+0.05x
0.05x=3.75
x=3.750.05=75 mL

Thus, the total volume of 0.10M H2SO4
required = 25 𝑚𝐿 (for neutralizing
50 𝑚𝐿 𝑜𝑓 0.10 𝑀 𝑁𝑎𝑂𝐻) + 75 𝑚𝐿 (for
attaining the 0.05 𝑀 concentration)
= 100 𝑚𝐿
So, option (C) is the correct answer

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