Question

Suppose that you have a 60.0% solution of NaOH. How many milliliters of water must be added to 30.0 mL of this solution to prepare a 35.0% solution of NaOH?15.5 mL21.4 mL51.4 mL72.8 mLCan’t determine the concentration because you need the density of the solution

Answer 1

• 21.4 ml (second choice)

Step-by-step explanation:

1) Data:

a) C₁ = 60.0% (initial solution)

b) V₁ = 30.0 ml (initial solution)

c) C₂ = 0% (pure water)

d) V₂ = ? (pure water)

e) C₃ = 35.0% (final concentration)

2) Formula:

• C₁V₁ + C₂V₂ = C₃V₃
• V₁ + V₂ = V₃ (assuming volume addtivity)

3) Solution:

a) Substitute values in the first formula:

• 60.0% × 30 ml + 0 = 35% (30 ml + V₂)

b) Solve the equation (units are supressed just to manipulate the terms)

• 18 = 10.5 + 0.35V₂

• 0.35V₂ = 18 - 10.5 = 7.5

• V₂ = 7.5 / 0.35 = 21.4 ml ← answer