Solution ConcentrationSolution ConcentrationRead 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 concentrations1) % 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/L3 g H2O2/100 mL solution 3 g H2O2/100 g solution

Solution ConcentrationSolution Concentration2) Expressing concentrations in parts per million

(ppm) requires the unit on top to be 1,000,000 times smaller than the unit on the bottomE.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 = M1 x V1 = M2 x V2

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 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?

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 M9. .7 mol x 58.45 g/mol/.25 L/58.45g/mol = 2.8 M10. .335 L x .425 M/1 L = .142 M11. .25 L x 2.0 M/1 L = .50 M .50 M x 110.99 g/mol = 55.5 g12. .76 M x .25 L/4 M = .0475 L or 47.5 mL13. 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

16. .001 = X g/250 mL = .25 g magnesium sulfate

17. 2.7 g/75 mL = 0.036 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 practiceMore practice1. 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?