I. The Nature of Solutions
Solutions
A. Definitions
Solution - homogeneous mixture
Solvent - present in greater amount (usually liquid, like H20)
Solute - substance being dissolved
A. Definitions
Solute - KMnO4 Solvent - H2O
B. Solvation
Solvation – the process of dissolving
solute particles are separated and pulled into solution
solute particles are surrounded by solvent particles
B. Solvation
StrongElectrolyte
Non-Electrolyte
solute exists asions only
- +
salt
- +
sugar
solute exists asmolecules
only
- +
acetic acid
WeakElectrolyte
solute exists asions and
molecules DISSOCIATION IONIZATION
View animation online.
B. Solvation
Dissociation› separation of an ionic
solid into aqueous ions
NaCl(s) Na+(aq) + Cl–(aq)
B. Solvation
Ionization› breaking apart of
some polar molecules into aqueous ions
HNO3(aq) + H2O(l) H3O+(aq) + NO3–(aq)
B. Solvation
NONPOLAR
NONPOLAR
POLAR
POLAR
“Like Dissolves Like”“Like Dissolves Like”
B. Solvation
Soap/Detergent› polar “head” with long nonpolar “tail”› dissolves nonpolar grease in polar water
C. Solubility
SATURATED SOLUTION
no more solute dissolves
UNSATURATED SOLUTIONmore solute dissolves
SUPERSATURATED SOLUTION
becomes unstable, crystals form
concentration
C. Solubility
Solubility› maximum grams of solute that will dissolve
in 100 g of solvent at a given temperature› varies with temp› based on a saturated solution
C. Solubility
Solubility Curve› shows the
dependence of solubility on temperature
C. Solubility
Solids are more soluble at...› high temperatures.
Gases are more soluble at...
low temperatures &high pressures (Henry’s
Law).EX: nitrogen narcosis,
the “bends,” soda
II. Concentration
Solutions - Part II
A. Concentration
The amount of solute in a solution.
How can we describe or communicate concentration?› Qualitatively through words
(“black” coffee vs. “a light amber shade”)
› Quantitatively through numbers(2 sugars & 1 cream)
A. Calculating Concentration
With Percent (%) % by mass
› Medicated creams› Proactiv contains 2.5%
benzoyl peroxide by mass
% by volume› Usually used when
both solute & solvent are liquids
› Gasoline can contain up to 10% ethanol by volume
With Moles* Molarity (M) Molality (m) Mole Fraction (X)
** Most often used by chemists **
Parts› ppm, ppb - water
contaminants
(don’t talk about in here)
B. Formulas
solution of L
solute of moles(M)molarity
(mL) solution ofvolume
(grams)solute of massm/v %
(grams) solution of mass
(grams)solute of massm/m %
solution ofvolume total
solute ofvolume v/v %
solution of Moles
solute of MolesionMole Fract
Remember to multiply the % formulas by 100 OR move decimal two spots left
B. Formulas
solvent ofkg
solute of moles(m)molality
2211 VMVM
mass of solvent only
1 kg water = 1 L
water
kg 1
mol0.25 0.25m
C. Practice Problems (Molality)
Find the molality of a solution containing 75 g of MgCl2 in 250 mL of water.
75 g MgCl2 1 mol MgCl2
95.21 g MgCl2
= 3.2m MgCl2
0.25 kg water
kg
molm
C. Practice Problems (Molality)
How many grams of NaCl are req’d to make a 1.54m solution using 0.500 kg of water?
0.500 kg water
1.54 mol NaCl
1 kg water
= 45.0 g NaCl
58.44 g NaCl
1 mol NaCl
kg 1
mol1.5 1.5m
C. Practice Problems{Concentration by Percent (%)}
At a restaurant I saw a man put 7 packets of sugar into his cup of coffee. What is the percent by mass of sugar in this poor man’s coffee?› 1 packet of sugar = 4 grams› 1 cup of coffee = 180 grams
28 g sugar
(180 + 28) g= 13.5% sugar
C. Practice Problems (Mole Fraction (X) Example)
Find the mole fraction of sugar in the coffee of that now comatose man who has just come down off his 7 sugar packet high.› 0.08 moles sugar› 10 moles coffee
0.08 moles sugar
(10 + 0.08) total molesXsugar =
= 0.0079
Xcoffee = 1 – Xsugar = 1 – 0.0079 = 0.9921
C. Practice Problems (Mole Fraction (X) Example)
What is the mole fraction of each component in a solution in which 3.57 g of sodium chloride, NaCl, is dissolved in
25.0 g of water?
First, convert from mass of NaCl to moles of NaCl. 3.57 g NaCl x 1 mole NaCl = 0.0610857139 mole NaCl
58.44247 g NaClNext, convert from mass of water to moles of water.
25.0 g H2O x 1 mole H2O = 1.387710877 mole H2O 18.01528 g H2O
Substitute these two quantities into the defining equation for mole fraction.
XNaCl = 0.0610857139 mole NaCl = 0.0421630713 ~ 0.042 (0.0610857139 + 1.387710877) mol solution
Xwater = 1.387710877 mole H20 = 0.9578369287 ~ 0.96 (0.0610857139 + 1.387710877) mol solution
** Note the sum of the mole fractions for a solution will equal 1. **
2211 VMVM
D. Dilution Preparation of a desired solution by
adding water to a concentrate. Moles of solute remain the same.
D. Dilution Example
What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution?
GIVEN:
M1 = 15.8M
V1 = ?
M2 = 6.0M
V2 = 250 mL
WORK:
M1 V1 = M2 V2
(15.8M) V1 = (6.0M)(250mL)
V1 = 95 mL of 15.8M HNO3
E. Preparing Solutions 500 mL of 1.54M
NaCl
500 mLwater
45.0 gNaCl
mass 45.0 g of NaCl add water until total
volume is 500 mL mass 45.0 g of NaCl add 0.500 kg of water
500 mLmark
500 mLvolumetric
flask
1.54m NaCl in 0.500 kg of water
E. Preparing Solutions
250 mL of 6.0M HNO3 by dilution› measure 95 mL
of 15.8M HNO3
95 mL of15.8M HNO3
water for
safety
250 mL mark
combine with water until total volume is 250 mL
Safety: “Do as you oughtta, add the acid to the watta!”
Solution Preparation Lab Turn in one paper per team. Complete the following steps:
A) Show the necessary calculations.
B) Write out directions for preparing the solution.
C) Prepare the solution.
For each of the following solutions:1) 100.0 mL of 0.50M NaCl
2) 0.25m NaCl in 100.0 mL of water
3) 100.0 mL of 3.0M HCl from 12.1M concentrate.
III. Colligative Properties Solutions – Part III
A. Definition
Colligative Property› property that depends on the
concentration of solute particles, not their identity
B. Types
Freezing Point Depression (tf)› f.p. of a solution is lower than f.p. of the
pure solvent
Boiling Point Elevation (tb)› b.p. of a solution is higher than b.p. of the
pure solvent
B. Types
View Flash animation.
Freezing Point Depression
B. Types
Solute particles weaken IMF in the solvent.
Boiling Point Elevation
B. Types
Applications› salting icy roads› making ice cream› antifreeze
cars (-64°C to 136°C) fish & insects
C. Calculations
t:change in temperature (°C)k: constant based on the solvent
(°C·kg/mol)m: molality (m)n: # of particles
t = k · m · n
C. Calculations # of Particles
› Nonelectrolytes (covalent) remain intact when dissolved 1 particle
› Electrolytes (ionic) dissociate into ions when dissolved 2 or more particles
C. Calculations At what temperature will a solution that is
composed of 0.73 moles of glucose in 225 g of phenol boil?
m = 3.2mn = 1tb = kb · m · n
WORK:
m = 0.73mol ÷ 0.225kg
GIVEN:b.p. = ?tb = ?
kb = 3.60°C·kg/moltb = (3.60°C·kg/mol)(3.2m)(1)
tb = 12°C
b.p. = 181.8°C + 12°C
b.p. = 194°C
C. Calculations Find the freezing point of a saturated
solution of NaCl containing 28 g NaCl in 100. mL water.
m = 4.8m
n = 2
tf = kf · m · n
WORK:
m = 0.48mol ÷ 0.100kg
GIVEN:
f.p. = ?
tf = ?
kf = 1.86°C·kg/mol
tf = (1.86°C·kg/mol)(4.8m)(2)
tf = 18°C
f.p. = 0.00°C - 18°C
f.p. = -18°C
IV. Total and Net Ionic Equations
Solutions – Part IV
Total Ionic Equations
Once you write the molecular equation (synthesis, decomposition, etc.), you should check for reactants and products that are soluble or insoluble (determine states of matter, which stay the same throughout reaction).
Use a solubility table to tell us what compounds are aqueous (dissolved in water), solids, liquids, and/or gases
We usually assume the reaction is in water If the compound is soluble (does dissolve in
water), the the compound splits into its ions If the compound is insoluble (does NOT dissolve
in water), then it remains as a compound
Steps to Writing Net Ionic Equations
1. Write a balanced chemical (molecular) equation2. Consult the solubility rules (along with strong acids
and strong bases) and assign the correct state of matter symbol annotation
3. Write the Total Ionic Equation (T.I.E)a. All compounds that are annotated (aq) break up into
individual cations and anions in that order
4. Eliminate spectator ionsa. Spectator ions-those ions that do not participate in the
chemical reaction but are present in the reaction mixtureb. Spectator ions are in the same form on each side of the
equation arrow
5. Write the Net Ionic Equation (N.I.E)a. The convention is to write the cation first followed by the
anion on the reactants side
Strong Acids and Strong Bases
Strong Acids› Hdrochloric acid -
HCl› Nitric acid - HNO3
› Sulfuric acid - H2SO4
› Hydrobromic acid - HBr
› Hydroiodic acid - HI› Chloric acid - HClO3
› Perchloric acid - HClO4
A strong acid is an acid that ionizes completely in water; weak ones DO NOT ionize!
Strong Bases› Lithium Hydroxide –
Li(OH)› Sodium Hydroxide –
Na(OH)› Potassium Hydroxide –
K(OH)› Calcium Hydroxide –
Ca(OH)2
› Rubidium Hydroxide – Rb(OH)
› Strontium Hydroxide – Sr(OH)2
› Cesium Hydroxide – Cs(OH)
› Barium Hydroxide – Ba(OH)2
Solubility Table
Solubility Rules
Total Ionic Equations
Molecular Equation:K2CrO4 + Pb(NO3)2 PbCrO4 + 2 KNO3
Soluble Soluble Insoluble Soluble
Total Ionic Equation:2 K+ + CrO4 -2 + Pb+2 + 2 NO3
- PbCrO4 (s) + 2 K+ + 2 NO3
-
Net Ionic Equation:CrO4 -2 + Pb+2 PbCrO4 (s)
Potassium chromate mixes with lead (II) nitrate
More ExamplesBalanced Chemical Equation:
Pb(NO3)2(aq) + 2NaI(aq) PbI2(s) + 2NaNO3(aq)
“Complete Ionic” Equation:Pb2+
(aq) + 2NO3-(aq) + 2Na+
(aq)+ 2I-(aq) PbI2(s) + 2Na+
(aq) +
2NO3- (aq)
Cancel the “spectator ions” that appear on both sides of the arrow
Pb2+(aq) + 2NO3
-(aq) + 2Na+
(aq)+ 2I-(aq) PbI2(s) + 2Na+
(aq) +
2NO3- (aq)
“Net Ionic” Equation:Pb2+
(aq) + 2I-(aq) PbI2(s)
Tips/Hints
States of matter assigned in the molecular equation stay the same throughout the T.I.E. and the N.I.E.
Solids, liquids, and gases DO NOT ionize
Gases keep their subscript (it doesn’t become a coefficient like other compounds)› For example: H2, Br2, Cl2, etc. stay like this
They don’t become 2H-1, 2Br -1, 2Cl -1