# What mass of salt must be dissolved in 250 g of water to obtain a 10% solution?

July 29, 2021 | education

| Let’s determine how much salt needs to be added to the solution:

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 (solution) = m (in-va) + m (H2O)

We denote m (in-va) = x, then the mass of the solution:

m (solution) = x + m (H2O) = x + 250

Let’s substitute all this in the formula for determining the mass of a substance:

x = 10 * (x + 250) / 100

x = 0.1 * (x + 250)

x = 0.1 * x + 25

x-0.1x = 25

x * (1-0.1) = 25

x = 25 / 0.9 = 27.8 g

Answer: you need to take 27.8 g of salt.

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