Transcript Chapter 11: Solutions and Their Properties

Chapter 11b: Solutions and Their
Properties
Introduction
1. A mixture is any intimate combination of two or more pure
substances
2. Can be classified as heterogeneous or homogeneous
Heterogeneous
-The mixing of components is visually
nonuniform and have regions of different
composition
Homogenous
-Mixing is uniform, same composition
throughout
-Can be classified according to the size of their
particles as either solutions or colloids
What is a solution?
Sugar + water
Solution Formation
Solute
• Dissolved substance, or smaller quantity substance
Solvent
• Liquid dissolved in, larger quantity substance
Saturated solution
• Contains the maximum amount of solute that will
dissolve in a given solvent.
Solution Formation
Unsaturated
Contains less solute than a solvent has the capacity
to dissolve.
Supersaturated
Contains more solute than would be present in a
saturated solution.
Crystallization
The process in which dissolved solute comes out of
the solution and forms crystals.
Units of Concentration
Molarity; Mole Fraction; Mass percentage; Molality.
Units of Concentration
Molarity (M)
M = mole of solute / Liter of solution
Molality (m)
m = moles of solute/mass of solvent (kg)
Mole Fraction (x)
X = mole of component / total moles
Units of Concentration
Mass Percent (mass %)
Mass % =
(mass of component / total mass of sol’n) x 100%
Parts per million, ppm =
(mass of component / total mass of solution) x 106
Parts per billion, ppb =
(mass of component / total mass of solution) x 109
Molarity (M)
Advantage:
amounts of solute can be measured by volume rather than by
mass.
Disadvantage:
Exact concentration depends on temperature
Because the volume of a solution expands or contracts as the
temperature changes.
• Mass percentage:
Mass% =
mass of component
-----------------------x 100%
total mass of solution
What is the mass percentage of glucose in a solution
prepared by dissolving 10g of glucose into 100g of
water?
10 g
Mass % glucose = -------------- x 100% = 9.09 mass%
10g + 100g
For traces:
Parts per million ppm
mass of component
ppm =
---------------------------total mass of solution
1 ppm = 1 mg/L
x 106
Parts per billion ppb
ppb
=
mass of component
---------------------------total mass of solution
1 ppb = 1 mg/L or 1 mg/1000L
x 109
Molality (m)
moles of solute
m = ----------------------mass of solvent (kg)
For a 1 m solution of KBr dissolve 1 mol KBr (119g) in
1 kg water.
Advantage:
Disadvantage:
only masses, independent on temp.
amounts must be measured by mass
and not by volume
What is the molality of a solution prepared by
dissolving 0.385 g of cholesterol, C27H46O in
40.0 g of chloroform, CHCl3?
Cholesterol = 386.7 amu ; chloroform = 119.4 amu
What is the mole fraction of cholesterol
in the solution?
What is the molality of a solution prepared by
dissolving 0.385 g of cholesterol, C27H46O in
40.0 g of chloroform, CHCl3?
Cholesterol = 386.7 amu ; chloroform = 119.4 amu
moles cholesterol
0.385g / 386.7
Molality = ---------------------------- = ----------------------- = 0.0249 mol/kg
kg chloroform
0.04 kg
What is the mole fraction of cholesterol
in the solution?
0.385g / 386.7
Xchloroform = -------------------------------- = 2.96 x 10-3
0.385g/386.7 + 40/119.4
Assuming that seawater is an aqueous solution of NaCl
what is its molarity? The density of seawater is 1.025 g/mL
at 20C and the NaCl concentration is 3.50 mass %
Assuming that seawater is an aqueous solution of NaCl
what is its molarity? The density of seawater is 1.025 g/mL
at 20C and the NaCl concentration is 3.50 mass %
3.5 mass% = 35 g NaCl in 1 kg solution
1 kg solution = m/d = 1000/1.025 = 975.6 mL
35 g / (23+35.5) 0.598
Molarity = --------------------- = ----------- = 0.61 mol/L = 0.61 M
0.9756 L
0.9756
Example 3
What is the mass % concentration of a saline sol’n
prepared by dissolving 1.00 mol of NaCl in 1.00
L of water? DensityH2O=1.00 g/mL MMNaCl =
58.443 g/mol
Ans: 5.52%
Example 4
Assuming that seawater is an aqueous solution of
NaCl what is its molarity? The density of
seawater is 1.025 g/mL at 20C and the NaCl
concentration is 3.50 mass %
• Assume 1 L to make easier, 1000 mL
• Ans: 0.615M
Example 5
What is the molality of a solution prepared by
dissolving 0.385 g of cholesterol, C27H46O in 40.0
g of chloroform, CHCl3? What is the mole
fraction of cholesterol in the solution?
• Ans: m = 0.0249m , X = 2.96 x 10-3
Example 6
What mass in grams of a 0.500 m solution of sodium acetate,
CH3CO2Na, in water would you use to obtain 0.150 mol
of sodium acetate?
• Assume 1 kg
Example 7
The density at 20°C of a 0.258 m solution of
glucose in water is 1.0173 g/mL and the molar
mass of glucose is 180.2 g/mol. What is the
molarity of the solution?
• Assume 1 kg
Example 8
The density at 20°C of a 0.500 M solution of acetic
acid in water is 1.0042 g/mL. What is the
concentration of this solution in molality? The
molar mass of acetic acid, CH3CO2H, is 60.05
g/mol.
• Assume 1 L
• 1.36 g of MgCl2 are dissolved in 47.46 g of
water to give a solution with a final volume
of 50.00 mL. Calculate the concentration of
the solution in mass %, ppm, mole fraction,
molarity, and molality.
• Hydrochloric acid is sold as a concentrated
aqueous solution. The concentration of
commercial HCl is 11.7 M and its density is
1.18 g/mL. Calculate the mass percent of
HCl in the solution. Calculate the molality
of the solution.
• Concentrated sulfuric acid has a density of
1.84 g/mL and is 18 M. What is the mass %
H2SO4 in the solution? What is the molality
of H2SO4 in the solution?