Calculate the amount of diluent to make 100 ml of a 20% solution from a stock solution that's 80%

75 mL

Step-by-step explanation:

The key point to remember is that the amount of solute is the same in each solution.

amount of solute = concentration

c₁V₁ = c₂V₂    

  V₂= V₁ × c₁/c₂

Data:

V₁ = 100 mL

c₁ = 20 %; c₂ = 80 %

Calculations:

(a) V₂

V₂ = 100 × (20/80) = 25 mL

(b) Added diluent

You have 25 mL of stock solution, and you want 100 mL of dilute solution, so you add 75 mL of diluent.