A chemist mixes some 20% acid solution with pure 100% acid to increase the concentration. How much pure acid and acid solution should be mixed to form 100 milliliters of 40% acid solution?

Answer 1

Let X be the volume of weak acid and Y be the volume of pure acid

X + Y = 100 (ml)
0.2X + Y = 0.4*100 ml (amount of pure acid in the mixture)

0.8X = 60
X = 75 ml
Y = 25 ml