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Concentration

Concentration. Solution Concentration. Read 509-515. 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,

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Concentration

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  1. Concentration

  2. Solution Concentration Read 509-515. 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 3gH2O2/100mLsolution  3gH2O2/100gsolution

  3. 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.

  4. FORMULAS Molarity = moles solute/liters solution Moles of solute = M1 x V1 = M2 x V2 Percent by volume = volume solute/solution volume x 100% Percent by mass = mass solute/solution volume x 100%

  5. 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.

  6. PROBLEMS FROM CHAPTER 18, SECTION 12 8. 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 0.425 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?

  7. 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?

  8. SOLUTIONS FOLLOW

  9. 36 g/180g/mol/2.0 L = 0.1 M 9. .7 mol x 58.45 g/mol/.25 L/58.45g/mol = 2.8 M 10. .335 L x .425 M/1 L = .142 M 11. .25 L x 2.0 M/1 L = .50 M .50 Mx 110.99 g/mol = 55.5 g 12..76 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. 14. 10 mL/200mL = .05 x 100% = 5% 15. .03 = X/400 mL = 12 mL

  10. 16. .001 = X g/250 mL = .25 g magnesium sulfate 17. 2.7 g/75 mL = 0.036 x100% = 3.6 % copper (II) sulfate

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

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