Question

Item 20
A chemist has 0.5 liters of an acid solution whose acid concentration is 30%. How many liters of pure water should be added to lower the concentration to 25%?

Answer 1

If the acid concentration of the 0.5 L acid solution is 30%, that means that the amount of acid in the solution is 30% of 0.5, right?
That would be... 0.15 Liters. We want the solution to have 25% acid concentration. Now, 25% is the same as 1/4, so the total volume would have to be 4 times the acid volume of 0.15.
So, what do we need the total volume to be (without changing the amount of acid, of course)? And in that case, how much water should we add?

@vocaloid did I do good?

Answer 2

If added water volume is x then you would have an equation:
0.5*0.3 = (0.5 + x)*0.25
Solve for x to get the answer