Answer
12.5 ml of acid must be added in the solution.
Work Step by Step
Let X represent the amount of acid to be added in the 100ml solution.
After this amount is added, we obtain a solution with a 20% acid concentration.
We use the following guideline to solve this problem:
Amount of pure acid in original solution + Amount of pure acid to be added = Amount of pure acid in final solution.
So: 10% $\times$ 100ml + X = 20% $\times$ (100+X)
.1 x 100mL+X= .2 x (100+X)
10 + X = 20 + $\frac{X}{5}$
10 = X - $\frac{X}{5}$
10 = $\frac{4X}{5}$
Multiply both sides by 5
50 = 4X
Divide both sides by 4
X = 12.5 ml
12.5 ml of acid must be added in the solution.
