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MOLARITY, MOLALITY, DILUTIONS & PERCENTS MOLARITY, MOLALITY, DILUTIONS & PERCENTS

Molarity • Molarity involves a molar amount of solute, so if you are given Molarity • Molarity involves a molar amount of solute, so if you are given something like grams, you must convert them into moles first. mols M L • Molarity also involves the volume (in liters) of total solution, so if you are given something like m. L, you must convert them into liters first.

1. Set up a “column of information” that lists the info given in the 1. Set up a “column of information” that lists the info given in the problem, as well as which variable you are solving for (the ? ) 2. Decide which rearrangement of the formula you need to solve the problem 3. Convert units given to those needed to match the units M= in the formula mol 4. Plug in the values and solve! L Ex 1 (Molarity): What is the molarity of 1 mol L 3 PO 4. 554 a 2. 3 H solution 54. 3 g ? = containing 54. 3 g of H 3 POPO 4 mol H 3 4? 54. 3 g → mol. 55 97. 9952 g H 3 PO 4 M = _____ 4 2. 3 L H 3 PO 4 M =. 24 mol = _____ M = mol =. 554 L = _____ L mol 2. 3 L

Dilution When chemists purchase solutions, they generally purchase “stock solutions” which are extremely concentrated Dilution When chemists purchase solutions, they generally purchase “stock solutions” which are extremely concentrated solutions This way a chemist can dilute the strong solution to any concentration that they wish. This stops the chemist from having to buy several concentrations M 1 V 1 = M 2 V 2 There are four parts to the dilution equation: 1. M 1 = Molarity of the diluted (or desired) solution 2. M 2 = Molarity of the concentrated (or stock) solution 3. V 1 = volume of the diluted (or desired) solution 4. V 2 = volume of the concentrated (or stock) solution

1. Set up a “column of information” that lists the info given in the 1. Set up a “column of information” that lists the info given in the problem, as well as which variable you are solving for (the ? ) 2. Decide which rearrangement you need to solve the problem V 2 = M 1 V 1 3. Convert units given to those needed to match the units in M 2 the formula 4. Plug in the values and solve! 3. 8 M Ex 3 (Dilution): How many m. L of 12 M HCl is needed to 12 M V 2 solution V 2 = 3. 8 M)(1. 5 L). 475 L produce 1. 5 L of a = M 1 V 1 that is (3. 8 M? = 1. 5 L = M 1 = _____ M 2 12 M ? M 2 = _____. 475 L 1000 m. L 475 m. L = HCl V 1 = _____ 1 L V 2 = _____

Concentration The amount of solute in a solution. Describing Concentration % by mass - Concentration The amount of solute in a solution. Describing Concentration % by mass - medicated creams % by volume- rubbing alcohol

Percent by Mass Remember … % = part x 100 whole % by mass Percent by Mass Remember … % = part x 100 whole % by mass = mass solute x 100 mass solution

Example What is the % by mass of a solution with 3. 6 g Example What is the % by mass of a solution with 3. 6 g of Na. Cl dissolved in 100. 0 g of water? % = (3. 6 / 103. 6) x 100 = 3. 5% Na. Cl

Percent by Volume u. Remember … u% = part x 100 whole u% by Percent by Volume u. Remember … u% = part x 100 whole u% by volume = volume solute x 100 volume solution

Example u. What is the % by volume of 75. 0 m. L of Example u. What is the % by volume of 75. 0 m. L of ethanol dissolved in 200. 0 m. L of water? u% = (75. 0 / 275. 0) x 100 = 27. 3%