More Concentrations ppmppb molarity and dilutions Learning Goals

More Concentrations (ppm/ppb, molarity and dilutions) Learning Goals: I will be able define ppm and ppb units and apply knowledge of them to perform the necessary calculations to solve for very small concentrations I will be able to define what molar concentration (molarity) means, and apply it to solve for the molar concentration of a given solution, as well as unknowns in diluted solutions

Very Small Concentrations (ppm and ppb) Very dilute solutions have concentrations much less than 1% (m/m) Use ppm (parts per million) or ppb (parts per billion) for these 6 mass of solute x 10 ppm= mass of solution 9 mass of solute x 10 ppb= mass of solution

Example: ppb problem Cadmium is a highly toxic metal. The average level of cadmium in the blood of Canadians is about 0. 35 ppb. At this level, what mass of cadmium would be present in 1. 5 kg of blood? (Convert units to grams first!)

Example # 2: ppm problem Health Canada’s guideline for max mercury levels in fish is 0. 5 ppm. When a 1. 6 kg salmon was tested, it was found to contain 0. 6 mg of Hg. Would this salmon be safe to eat? (Convert units to grams first!)

You Try: ppb/ppm problem House paint produced in Canada must contain less than 600 ppm of lead. What is the maximum mass of lead permitted in a can that contains 7. 0 kg of paint? (Convert units to g!)

Molar Concentrations

Molar Concentrations Also known as Molarity: the number of moles of solute that can dissolve in 1 L of solution. Molar concentration (mol/L) = Amount of solute (mol) Volume of solution (L) c= n/v n c V

Example #1: Calculating Molarity What is the concentration, in mol/L, of a solution formed by dissolving 28. 0 g of calcium chloride in enough water to make 225 m. L of solution? (Find n. Ca. Cl 2 first using M, then c)

Example #2: Calculating Molarity How many grams of sodium nitrate would be needed to make 425 m. L of 6. 00 mol/L solution? (Find n first using n=c. V, then m using m=nx. M)

You Try #1: Calculating Molarity What final solution volume would be required to prepare A 0. 100 mol/L solution of Ag. NO 3(aq) if 1. 20 g of the solid salt will be used? (Find n. Ag. NO 3 first, then use V=n/c to find V)

You Try #2: Calculating Molarity A solution of sodium chloride in water contains 14. 0 g of Na. Cl dissolved in 250 m. L of solution. What is the molarity of the solution?

Preparing Solutions in a Lab We can prepare standard solutions (a solution of an accurate, known concentration) from stock solutions (a concentrated solution) by using a volumetric flask (glassware that is used to make a liquid solution with an accurate volume) Watch video on preparing standard solutions using volumetric flasks: http: //www. youtube. com/watch? v=A 2 Yy. Io 8 v. SCA

Preparing Diluted Solutions If dilute solutions are prepared accurately, no mass will be lost, and therefore the amount of moles will stay the same. Using c=n/v, we can rearrange to get n=c. V, and since n is not changing if we dilute a solution, the formula below arises: c 1 V 1=c 2 V 2 Where c 1 = initial concentration of solution before dilution v 1 = volume of solution before dilution c 2 = final concentration of solution after dilution v 2 = volume of solution after dilution

Example #1: Dilution Calculations Your teacher has a stock solution of 12 mol/L HCl (aq). A class experiment requires 2. 0 L of 0. 10 mol/L of hydrochloric acid. What volume of concentrated solution should be used to make the dilute solution for the experiment?

You Try: Dilution Calculations What volume of 1. 25 mol/L KI solution can you make with 125 m. L of 3. 00 mol/L potassium iodide solution?

How did we do? Learning Goals: I will be able define ppm and ppb units and apply knowledge of them to perform the necessary calculations to solve for very small concentrations I will be able to define what molar concentration (molarity) means, and apply it to solve for the molar concentration of a given solution, as well as unknowns in diluted solutions