Question

20 ml of H2SO4 sol neutralises 21.2ml of 3% sol. of Na2CO3
How much water should be added to each 100ml of the
sol. to bring down its strength to decinormal.​

Answer 1

Explanation:

Here is (one way) how to figure out this kind of problem, explained for future use:

The number of moles in the concentrated solution you add is the same as the number of moles in the final solution: n1 = n2

To get the number of moles, we can multiply our concentration by our volume: C1V1 = C2V2

And rather than having a molar concentration, you have a percent - so the easiest thing is to consider that as a fraction:

C1 = 98% = 0.98

C2 = 1,5% = 0.015

Using this and the known final volume (V2 = 200 ml), you can calculate the volume of concentrated acid to add:

V1 = 3.06 ml

Which is added to (200 - 3.06 =) 196.94 ml of water

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