**Lesson 3&4 - % and Molar Concentrations of Solutions** • Concentration • Volume/volume percent • Mass/volume percent • Ppm • Ppb • Mass/mass percent

**Concentration** • The amount of solute per quantity of solvent • Eg. Beer = 5-9% alcohol, spirits = 40%, Everclear is a colorless and flavorless type of grain alcohol= 95% = illegal in Canada and most States. • Phenol = as little as 1g can be fatal, although it is found in low concentrations in throat spray and lotions to relieve itching.

**Ppm and Ppb** • Ppm – • Ppb – • 1ppm = 1ml of something per 1000L of water • 1ppm = 1mg of something per 1kg of soil • 1ppb = 1ml of something per 1 000 000L of water or 1mg of something per 1000Kg of soil

**Examples** • Lead in drinking water – anything greater than 15ppb is considered hazardous. • Ozone can harm lungs at anything over 0.12ppm

**Mass/Volume Percent** • Unsaturated solutions are often expressed as the mass of solute dissolved per volume of solvent. • Mass/volume percent gives the mass of solute dissolved in a volume of solution, expressed in percent.

**Sample Problem Mass/Volume** • A pharmacist adds 2.0mL of distilled water to 4.00g of a powered drug. The final volume of the solution is 3.00mL. What is the concentration of the drug in g/100mL of solution? What is the percent (m/v) of the solution?

**Sample Problem (m/v)** • Many people use a solution of trisodium phosphate, Na3PO4, (TSP) to clean walls before putting up wall paper. The recommended concentration is 1.7%(m/v). What mass of TSP is needed to make 2.0L of solution?

**Concentration as a Mass Percent** • The concentration of a solution that contains a solid solute dissolved in a liquid solvent can also be expressed as a mass of solute dissolved in a mass of solution. • A mass/mass percent gives the mass of a solute divided by the mass of a solution, expressed as a percent

**Sample Problem mass/mass %** • Calcium chloride, CaCl2, can be used instead of road salt to melt ice on roads. To determine how much calcium chloride was on the road, a student took a sample to analyze. The sample had a mass of 23.47g. When the solution was evaporated, the residue had a mass of 4.58g. What was the mass/mass percent of calcium chloride in the slush? How many grams of CaCl2 were present in 100g of solution?

**Concentration as a volume/volume %** • When mixing two liquids to form a solution, it is easier to measure their volumes than their masses • v/v % gives the volume of solute divided by the volume of the solution, expressed as a percent.

**Sample Problem v/v%** • Rubbing alcohol is commonly used as an antiseptic for small cuts. It is sold as a 70% (v/v) solution of isopropyl alcohol in water. What volume of isopropyl alcohol is used to make 500mL of rubbing alcohol?

**Molar Concentrations of Solutions** • Molar concentration = the number of moles of solute in 1L of solution, also known as molarity. • Molar concentration (mol/L) = amount of solute (mol) / volume of solution (L)

**Review! Grams to Moles!** • Convert 100g of Ca(OH)2 to moles

**Sample Problem** • What is the concentration in moles per litre of a solution containing 0.65mol of NaNO3 in 2500mL of solution? • Given: 0.65 mol NaNO3, 2500mL = 2.5L • Required: mol/L

**Sample Problem** • What is the concentration in moles per litre of a solution containing 49g of sulfuric acid (H2SO4) dissolved in 3.0L of solution? • ANS = 0.17mol/L

**Sample Problem** • A saline solution contains 0.90g of sodium chloride dissolved in 100mL of solution. What is the molar concentration of the solution? • ANS = 0.15mol/L

**Last Sample Problem** • At 20DC a saturated solution of calcium sulphate, CaSO4, has a concentration of 0.0153mol/L. A student takes 65mL of this solution and evaporates it. What mass (g) is left in the evaporating dish?