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Concentration: Determining molarity from grams of solute and volume of solution.


Example 1: Molarity from grams of solute and volume of solution

What is the molarity of a solution made using 45.0 g of NaCl and enough water to give 1 liter of solution? click for answer


Step 1

Write out the definition for molarity. M = moles solute/ liters of solution

Step 2

Tabulate the quantities given in the question

volume of solution

1.00 liter

molar mass of solute

1.00 mol NaCl = 58.5 g NaCl

Step 3

Calculate the mols of solute from grams and molar mass of solute.

moles of solute

(45.0 g NaCl)x(1 mole NaCl / 58.5 g NaCl) = 0.796 mols NaCl

Step 4

Substitute into the definition for molarity. Because the volume is 1 Liter, the molarity and number of mols of solute are the same.

M = 0.796 moles NaCl / 1.00 liters of solution = 0.796 M NaCl

Molarity = [0.796 mols NaCl][1 / 1.00 L ] = 0.796 mols NaCl / L


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