Concentration

Concentration – amount of solute per quantity of solvent Ways to express the concentration of a solution Concentration as a Mass/Volume Percent Concentration as a Mass/Mass Percent Concentration as a Volume/Volume Percent Concentration as ppm Concentration as ppb Concentration as molarity (mols/L)

Mass/Volume Percent Mass of solute dissolved in a volume of solution, expressed as a % Mass/volume percent = x 100% Example: Saline solution contains 0.9g of sodium chloride dissolved in 100 mL of solution or 0.9% Mass of solute (in g) Volume of solution (in mL)

What is the percent (m/v) of the solution? A pharmacist adds 2.00 mL of distilled water to 4.00g of a powdered drug. The final volume of the solution is 3.00 mL. What is the percent (m/v) of the solution? Mass/volume percent= x 100% = x 100% mass of solute (in g) Volume of solution (in mL) 4.00 g 3.00 mL = 133%

Many people use a solution of trisodium phosphate to clean walls before putting up wall paper. The recommended concentration is 1.7% (m.v). What mass of TSP is need to make 2.0 L solution? Mass of solute (g) Volume of solution (in mL) (m/v) percent = x 100% rearrange the equation to solve for mass of solute Mass of solute= = (m/v) percent x volume of solution 100% 1.7% x 2000 mL 100% = 34 g

Concentration as a Mass/Mass percent Mass/mass percent gives the mass of a solute divided by the mass of a solution also referred to as percent (m/m) Mass/mass percent = x 100 % Mass of solute (in g) Mass of solution (in g)

Calcium chloride can be used instead of road salt to melt the ice on roads during the winter. To determine how much calcium chloride had been used on a road, a student took a sample of slush to analyze. The sample had a mass of 23.47 g. When the solution was evaporated, the residue had a mass of 4.58 g. What was the mass/mass percent of calcium chloride in the slush? Mass of solute (in g) Mass of solution (in g) Mass/mass percent = x 100% = x 100% = The mass/mass percent was 19.5% (m/m) 19.5 g of calcium chloride was dissolved in 100 g of solution 4.58 g 23.47 g 19.5 %

Concentration as a Volume/Volume Percent Volume/volume percent gives the volume of solute divided by the volume of solution Also referred to as percent (v/v), volume percent concentration Volume/volume percent = x 100% volume of solute (in mL) Volume of solution (in mL)

Volume/volume % x volume of solution 100% Rubbing alcohol is commonly used as an antiseptic for small cuts. It is sold as 70% (v/v) solution of isopropyl alcohol in water. What volume of isopropyl alcohol is used to make 500 mL of rubbing alcohol? Using this equation, Volume/volume percent = x 100 % Rearrange to solve for volume of solute: Volume of solute = = 350 mL of isopropyl alcohol is used to make 500 mL of 70% (v/v) rubbing alcohol. volume of solute Volume of solution Volume/volume % x volume of solution 100% 70% x 500 mL 100% = 350 mL

Concentration in parts per million or parts per billion ppm – parts per million (106)(one part solute per million parts of solution) ppb – parts per billion (109)(one part solute per billion parts of solution) Usually mass/mass relationships ie. The mass of solute compared with the mass of solution. ppm = x 106 OR mass of solute (g) Mass of solution (g) x g 106 g of solution Mass of solute Mass of solution =

Mercury poisoning becomes apparent when a person build up more than 20 Mercury poisoning becomes apparent when a person build up more than 20.mg of Mercury in their body. Express this amount as ppm for a 60.kg person You must first convert everything into grams 20mg/1000g = 2.0 x 10-2 g 60kg/1000g = 6.0 x 104 g Ppm = mass solute x 106 mass solution = 2.0 x 10-2 g x 106 6.0 x 104 g = (3.33 x 10-7g) x 106 = .33 ppm

Homework 8.6 Homework- molarity 8.7 Homework % concentration