How many grams of water do you need to evaporate from 300 g of a 15% potassium hydroxide solution to double its concentration?

ω = m (substance) / m (solution)
Find the mass of alkali
m = 300 * 0.15 = 45 g
ω = m (substance) / m (solution), let x be the mass of water that needs to be evaporated, then:
0.3 = 45 / (300 – x)
90 – 0.3x = 45
x = 150 g

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