# What mass of a solution with a mass fraction of potassium hydroxide of 20% should be added to 1 kg of a solution

August 17, 2021 | education

| **What mass of a solution with a mass fraction of potassium hydroxide of 20% should be added to 1 kg of a solution with a mass fraction of KOH of 50% to obtain a solution with a mass fraction of KOH of 25%?**

Given:

ω1 (KOH) = 20%

m2 solution (KOH) = 1 kg

ω2 (KOH) = 50%

ω3 (KOH) = 25%

To find:

m1 solution (KOH) -?

1) To solve such a problem, the most optimal would be to use the cross rule (mixing rule, diagonal model of the “Pearson envelope”)

2) Calculate the mass of a 20% KOH solution, making the proportion:

5 kg of 50% KOH solution – 25 kg of 20% KOH solution;

1 kg of 50% KOH solution – x kg of 20% KOH solution;

m1 solution (KOH) = x = 1 * 25/5 = 5 kg.

Answer: The mass of the KOH solution is 5 kg.

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