Solution Concentration Read Try practice problems 8-17 (show work) Concentration = quantity of solute quantity of solution (not solvent) There are 3 basic ways to express concentration: 1) percentages, 2) very low concentrations, and 3) molar concentrations 1) % concentration can be in V/V, W/W, or W/V Like most %s, V/V and W/W need to have the same units on top and bottom. W/V is sort of in the same units; V is mostly water and water’s density is 1 g/mL or 1 kg/L 3 g H 2 O 2 /100 mL solution  3 g H 2 O 2 /100 g solution

Solution Concentration 2)Expressing concentrations in parts per million (ppm) requires the unit on top to be 1,000,000 times smaller than the unit on the bottom E.g. 1 mg/kg or  g/g Multiples of 1000 are expressed in this order  _, m_, _, k_ (“_” is the base unit, e.g. g, L) Notice that any units expressed as a volume must be referring to a water solution (1L = 1kg) For parts per billion (ppb), the top unit would have to be 1,000,000,000 times smaller 3)Molar concentration is the most commonly used in chemistry. Ensure that units are mol/L.

FORMULAS Molarity = moles solute/liters solution Moles of solute = M 1 x V 1 = M 2 x V 2 Percent by volume = volume solute/solution volume x 100% Percent by mass = mass solute/solution volume x 100%

Please attempt to work the following problems out before you look at the answers. REMEMBER: only practice will help you get better at Chemistry, so, don’t cheat yourself out of the opportunity to earn a better grade.

PROBLEMS FROM CHAPTER 18, SECTION A solution has a volume of 2 L & contains 36 g of glucose. What is the molarity of the solution? 9. A solution has a volume of 250 mL & contains 0.7 mol NaCl. What is its molarity? 10. How many moles of ammonium nitrate are in 335 mL of M solution? 11. How many moles of solute are in 250 mL of 2 M calcium chloride? How many grams of calcium chloride is this? 12. How many mL of a stock solution of 4 M KI would be needed to prepare 250 mL of 0.76 M KI? 13. You need 250 mL of 0.2 M NaCl, but all you have is a 1 M solution. How do you prepare the required solution?

14. If 10 mL of acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume in the solution? 15. A bottle of hydrogen peroxide is labeled 3%. How many mL of hydrogen peroxide is in a 400 mL bottle? 16. Calculate the grams of solute to make 250 mL of 0.1% magnesium sulfate. 17. A solution contains 2.7 grams of copper(II) sulfate in 75 mL of solution. What is the percent of the solution?

SOLUTIONS FOLLOW

8.36 g/180g/mol/2.0 L = 0.1 M 9..7 mol x g/mol/.25 L/58.45g/mol = 2.8 M L x.425 M/1 L =.142 M L x 2.0 M/1 L =.50 M.50 M x g/mol = 55.5 g M x.25 L/4 M =.0475 L or 47.5 mL 13. Use a pipette to transfer 50 mL of 1.0 M solution to a 250 mL volumetric flask, then fill with distilled water. 250 mL x.2 M = 50 mL mL/200mL =.05 x 100% = 5% = X/400 mL = 12 mL

= X g/250 mL =.25 g magnesium sulfate g/75 mL = x100% = 3.6 % copper (II) sulfate

10 g / 260 g = 3.8 % 30 mL / 280 mL = 11% (in reality may be off) 8.0 g / 100 g = 8% More practice 1.What is the % of copper in an alloy when 10 g of Cu is mixed with 250 g of Zn? 2.What is approximate % if 30 mL of pure ethanol is added to 250 mL of water? 3.What is the % if 8.0 g copper is added to enough zinc to produce 100 g of an alloy?