1. Aim # 44: How do we calculate the concentration of a solution?
H.W. # Study pp (sec. 11.1) Ans. ques. p. 544 # 29,32-35

2. I A solution is a homogeneous mixture e. g
I A solution is a homogeneous mixture e.g. salt water, ethanol + water, acetone + diethyl ether, brass (Cu + Zn), bronze (Cu + Sn)
II Solution components solvent- the component present in the greatest amount solutes)- all other components
III Types of solutions A. gaseous- two or more gases mixed uniformly e.g. air SO2, O2, and SO N2, H2, and NH3

3. B. Liquid- a liquid solvent (e. g. water) with 1. a gaseous solute (e
B. Liquid- a liquid solvent (e.g. water) with a gaseous solute (e.g. CO2) a liquid solute (e.g. ethanol, bromine) a solid solute (e.g. a salt, sucrose)
C. Solid- a solid solvent with a gaseous solute (e.g. H2 in Pd) a liquid solute (e.g. Hg in Ag)
3. a solid solute (e.g. steel, Ag in Au)
IV Solution concentrations- qualitative Dilute- a relatively small amount of solute Concentrated- a relatively large amount of solute

4. Solution concentrations- quantitative A. 1
Solution concentrations- quantitative A mass percent mass percent = mass solute x 100% mass solution
Problem: What is the mass % of sodium chloride in a solution formed by dissolving 25.0 g of NaCl in g of H2O?
Ans: mass% NaCl = x 100% = 4.76% g g

5. 2. parts per million (ppm) ppm = mass solute x mass solution (For the above solution, ppm = x 106 = 4.76 x 104 ppm)
Problem: Commercial bleach contains 3.26% sodium hypochlorite, NaOCl by mass. What is the mass of NaOCl in a bottle containing g of bleach?
Ans: % = mass NaOCl x g
mass NaOCl = 3.26 x = 81.5 g NaOCl

6. B. mole fraction (χ) mole fraction of = χA = moles of component component A total moles of all components
Problem: What is the mole fraction of HCl in a solution of 3.65 g HCl dissolved in 90.0 g H2O?
Ans: nHCl = 3.65 g HCl x 1 mol HCl = mol HCl g HCl nH2O = 90.0 g H2O x 1 mol H2O = 5.00 mol H2O g H2O
χHCl = nHCl = mol ͘ nH20 + nHCl mol mol χHCl = =

7. Ans: mass EtOH = 0.789 g/mL x 10.00 mL = 7.89 EtOH
Problem: An ethanol-water solution is prepared by dissolving mL of ethanol, CH3CH2OH, (density = g/ml) in a sufficient volume of water to produce mL of a solution with a density of g/ml What is the mole fraction of the ethanol in the solution?
Ans: mass EtOH = g/mL x mL = 7.89 EtOH
moles solution = g EtOH = .171 mol EtOH g/mol mass solution = g/ml x mL = 98.2 g solution mass H2O = 98.2 g solution – 7.89 g EtOH = g H2O moles H2O = g H2O = mol H2O g/mol χ = nEtOH = mol = nEtOH + nH2O mol mol

8. C. Molarity (M) M = molarity = moles solute liters solution What is the molarity of the ethanol solution above? M = nEtOH = mol = M Vsol L
D. molality (m)
m = molality = moles solute kg solvent Find the molality of the ethanol solution above Mass H2O = g = kg
m = nEtOH = mol = m kg H2O kg

9. IF YOU KNOW THE MOLARITY OF A SOLUTION YOU CAN CALCULATE THE MOLALITY, MOLE FRACTION, AND MASS % IF YOU ALSO KNOW ITS DENSITY
Problem: The molarity of a glycerol solution (C3H8O3 ) solution is M. if the density of the solution is 1.10 g/mL, calculate the molality, mole fraction, and mass % of the solution.
Ans: Assume you have 1 L of solution mass solution = 1.10 g/mL x 1000 mL = 1100 g solution
moles glycerol = .925 mol/L x 1 L = .925 mol glycerol
mass glycerol = .925 mol x g/mol = g glycerol
mass H2O = 1100 g – g = 1015 g = kg H2O
m = mol glycerol = 9.11 m kg H2O

10. moles H2O = 1015 g x 1 mol = mol g χ = mol = mol mol mass % = g glycerol x 100 = 77.4% g
Problem: Given that the density of a solution of 5.0 g toluene (C7H8) and 225 g of benzene (C6H6) is g/mL, calculate a) the molarity of the solution b) the mass percentage of the solute c) the molality of the solution d) the mole fraction of the solute

11. Ans: a) mass solution = 5. 0 g + 225 g = 230. g Vsol. = 230
Ans: a) mass solution = 5.0 g g = 230. g Vsol. = 230.g x 1 mL = 263 mL g
moles toluene = (5.0 g C7H8)(1 mol C7H8) = mol g C7H M = mol = 0.21 mol/L L
b) moles C6H6 = 225 g x 1mol = mol C6H g
χC7H6 = =
c) molality = mol C7H8 = .24 mol/kg kg C6H6
d) mass % = g C7H x = g x g C7H g C6H g = 2.2 %

12. converting molarity to molality
mass solvent
mass solute molar moles solute mass
mass solution
density
volume solution M

13. Practice Problems
Zumdahl (8th ed.) p. 532 # 36
p. 531 # 13-15
p. 536 # 98