Question

Calculate the mass of sodium sulphate required to prepare its 20% solution in hundred grams of water

Answer 1

Hello!  

We have the following data:

% m / m (mass percentage of solute per mass of solution) = 20

m1 (solute mass) = ? (in grams)

m2 (mass of the solvent) = 100 g

m (mass of solution)

It is known that the mass of solution is equal to the sum of the mass of the solute (m1) with the mass of the solvent (m2)  

We apply the data to the formula of the mass percentage of solute per mass of solution, see:

$\%\:m/m = \dfrac{m_1}{m}*100$

$\%\:m/m = \dfrac{m_1}{m_1+m_2}*100$

$20 = \dfrac{m_1}{m_1+100}*100$

$20*(m_1+100) = m_1*100$

$20\:m_1 + 2000 = 100\:m_1$

$2000 = 100\:m_1 - 20\:m_1$

$2000 = 80\:m_1$

$80\:m_1 = 2000$

$m_1 = \dfrac{200\diagup\!\!\!\!0}{8\diagup\!\!\!\!0}$

$\boxed{\boxed{m_1 = 25\:grams\:of\:sodium\:sulphate}}\Longleftarrow(solute\:mass)\end{array}}\qquad\checkmark$

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I Hope this helps, greetings ... Dexteright02! =)