Molarity

Molarity: What it is and how to calculate it

Textbook: page 481Molarity is a unit of concentration; it is a numerical way of saying exactly how much solute is present in a solvent Molarity is equal to the number of moles of solute divided by the liters of solution…

M = Moles of SoluteLiters of Solution

Example: What is the molarity of a solution that contains 5.5 moles of sodium chloride in 10.5 liters of solution?

Rules for finding Molarity of a Solute1. If you are given “grams”, use the molar mass of the compound to convert them to moles. 1 mole = # of g/mol2. If you are given a unit of volume; L, mL, cm 3 etc... just move the decimal to the left to convert from mL to Liters.

Example: If I have 3.5g of NaCl in 1250mL of a solution, what’s the molarity?

Rule 1 To convert g to mol, use the mole roadRule 2 To find molarity, convert g to mol and mL to L

M = 5.5 moles10.5 liters = .52 Molar

Rule 1

3.5g x 1mol = .060 mol 1 58.5g/mol

Rule 2 1250 mL = 1.25 litersNext… M= .060 mol = .048 M 1.25 L

Molarity

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