Calculate the masses of potassium hydroxide and water that are required to prepare a solution

| September 6, 2021 | education

Calculate the masses of potassium hydroxide and water that are required to prepare a solution weighing 80 grams with a mass fraction of alkali of 20%.

To begin with, we write down an expression to determine the mass fraction of a substance in a solution:
w (in-va) = (m (in-va) / m (solution)) * 100%
Let us express the mass of a substance from this expression:
m (in-va) = (w (in-va) * m (solution)) / 100%
m (KOH) = (w (KOH) * m (solution)) / 100%
Let’s calculate the mass of alkali in the solution:
m (KOH) = (w (KOH) * m (solution)) / 100% = 20 * 80/100 = 16 g.
Let’s find the mass of water:
m (solution) = m (water) + m (H2O)
m (solution) = m (KOH) + m (H2O)
m (H2O) = m (solution) -m (KOH) = 80-16 = 64 g.
Answer: you need to take 16 g of alkali and 64 g of water.



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