Answer:
22.86 ml.
Step-by-step explanation:
Let x ml of 5% sulfuric solution must Molly add to 20ml of 20% solution to get a 12% solution.
Now, x ml of 5% sulfuric acid solution has pure acid of [tex]\frac{5x}{100} = 0.05x[/tex] ml.
Again, 20 ml of 20% sulfuric acid solution has pure acid of [tex]\frac{20 \times 20}{100} = 4[/tex] ml.
Therefore, we can write the equation as
[tex]\frac{0.05x + 4}{20 + x} = \frac{12}{100} =0.12[/tex]
⇒ 0.05x + 4 = 2.4 + 0.12x
⇒ 0.07x = 1.6
⇒ x = 22.86 ml. (Answer) (Approximate value)
