Other Ways of Expressing the Concentration of Solutions percent concentration, ppm, ppb

Percentage Concentration Can be expressed as: 1.% mass/volume, or % m/v; 2.% mass/mass, or % m/m; 3.% volume/volume, or % v/v.

1. % mass/volume, or % m/v % m/v =mass of solute (g) 100 mL solution 1 —or— mass of solute (g) * 100% vol of solution (mL) 1 solution = solute + solvent

sample problem 1 What is the % concentration when 4.52 g KNO 3 is dissolved in 250 mL of solution? Answer: (4.52 g/250 mL) * 100% = 1.81% —or— 4.52 g=? g. 250 mL100 mL ? = 1.81 g/100 mL or 1.81 %

sample problem 2 Na 3 PO 4 is sold in hardware stores under the (incorrect) name “Trisodium phosphate”, or TSP. A 1.7% (m/v) solution of TSP is recommended for cleaning walls before painting or putting up wallpaper. What mass of TSP is needed to make 2.0 L of solution?

Answer: 1.7% (m/v) means 1.7 g per 100 mL or ? g per 2000 mL cross-multiplying gives ? =(1.7 g * 2000 mL)/100 mL =34 g Use 34 g TSP to make 2.0 L of cleaning sol’n. NB. Solutions of TSP are VERY BASIC. Wear Gloves!!

2. % mass/mass, or % m/m % m/m =mass of solute (g) 100 g solution 1 —or— mass of solute (g) * 100% mass of solution (g) 1 solution = solute + solvent

sample problem 3 CaCl 2 is often used as an ice-melter. If 45.3 g of slush (snow, ice, CaCl 2 ) was evaporated to yield 6.37 g CaCl 2, calculate the % m/m CaCl 2 in the slush. Here, the slush represents the solution. Answer: % CaCl 2 = (6.37 g CaCl 2 /45.2 g slush)*100% CaCl 2 = 14.1 % (m/m)

3. % volume/volume, or % v/v % v/v = volume of solute (mL) 100 mL solution 1 —or— volume of solute (mL) * 100% volume of solution (mL) 1 solution = solute + solvent

sample problem 4 Rubbing alcohol is a 70% (v/v) solution of isopropyl alcohol in water. What volume of isopropyl alcohol is required to prepare 350 mL of rubbing alcohol? Answer: 70 mL isopropyl alcohol=? mL 100 mL rubbing alcohol350 mL ? = (70 mL * 350 mL)/100 mL = 245 mL isopropyl alcohol in 350 mL

Practical Application The concentration of alcohol (ethanol) in alcoholic beverages is stated as % (v/v). Regular beer is 5.0% (v/v) ethanol; “lite” beer is 4.0% (v/v). Express the % ethanol in “lite” beer as % (m/v). What information do you need? Density of ethanol = 0.80 g/mL.

Answer: 4.0% (v/v) = 4.0 mL ethanol/100 mL We need to convert 4.0 mL ethanol  mass. 4.0 mL*(0.80 g·mL -1 ) = 3.2 g ethanol/100 mL % ethanol (m/v) in “lite” beer = 3.2% If you were the brewer, would you label % ethanol in “lite” beer as m/v or v/v?

ppm concentration* ppm =mass of solute * 10 6 mass of solution or mass of solute =. ? g. mass of solution10 6 g solution (*parts per million—10 6 )

ppb concentration* ppb =mass of solute * 10 9 mass of solution or mass of solute =. ? g. mass of solution10 9 g solution (*parts per billion—10 9 )

sample problem 5 Symptoms of mercury poisoning become apparent after the ingestion of more than 20 mg of Hg. For a 70 kg person, convert this to a)% m/m b)ppm c)ppb

Answer: a)% m/m = (20 x g/70 x 10 3 g) * 100% = 2.9 x is percent Hg in body b) ppm = (20 x g/70 x 10 3 g) * 10 6 = 0.29 ppm Hg c) ppb = (20 x g/70 x 10 3 g) * 10 9 = 2.9 x 10 2 ppb Hg

HW P 371 to 377, do several problems from each set.