# Chemistry

What is the mass percent of an aqueous sodium hydroxide solution in which the molality of NaOH is 6.25m? The density of the solution is 1.2219 g/mL

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1. molarity is the number of moles per unit volume (L).

6.25 m means 6.25 moles per L of solution, or per 1221.9 g of solution.

Calculate the mass density accordingly.

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2. Do you have a 6.25m or a 6.25M solution? Mathmate's answer and definition is for 6.25M.

The correct answer for 6.25m is below.
m is molality and the problem states molality (not molarity).
molality = mols solute/kg solvent.
6.25m means 6.25 mols NaOH/kg solvent.
g = mols x molar mass = 6.25 x 40 = about 250; therefore, you have a solution of 250g NaOH in (1000 + 250) or 250 g NaOH in 1250 g solution.
mass% = (250/1250)*100 = ?about 20%

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3. Thank you Dr. Bob.

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