We're being asked to determine the mass of Na_{2}SO_{4} needed to be added to 175 mL of water in order to make a 0.55 m solution

Recall that **molality** can be calculated as:

$\overline{){\mathbf{molality}}{\mathbf{=}}\frac{\mathbf{moles}\mathbf{}\mathbf{solute}}{\mathbf{kg}\mathbf{}\mathbf{solvent}\mathbf{}}}$

We can calculate for the mass of a Na_{2}SO_{4} using a *dimensional analysis* with proper conversion and using the molar mass and density provided.

How many __grams__ of Na _{2}SO_{4} (142.05 g/mol) should be added to 175 mL of water to prepare a 0.555 *m* solution of Na _{2}SO_{4}? Assume the density of water is 1.00 g/mL.

a. 201 g

b. 55.2 g

c. 13.8 g

d. 91.2 g

e. 54.2 g

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