What volume of water must be added to 0.5 l of 25% potassium hydroxide solution (density 1.25 g / ml) to obtain a 5% solution?

m = ρ x ω x V = 1.25 x 0.25 x 500 = 156.25 g KOH
m (H2O in this solution) = 500 x 1.25 = 625 g – 156.25 = 468.75 g
156.25 – 5%
x – 100%
x = (156.25 x 100) / 5 = 3125 g – total solution
m (water added) = 3125 – 625 = 2500 g or 2500 l.
Answer: 2500 liters of water needs to be added.

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