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Solutions Notes
Words to Know• Solution – homogenous mixture• Solvent – substance present in the largest amount• Solutes – substance present in the smallest amount• Aqueous solution – solutions with water as the
solvent• Concentration – the amount of solute in a given
volume of solution• Concentrated – large amount of solute dissolved in
solvent• Dilute – small amount of solute dissolved in solvent
• Saturated – a solution that contains as much solute as will dissolve at that temperature
• Unsaturated – a solution that hasn’t reached that limit of solute that will dissolve
• Supersaturated - a solution that contains more solute than should dissolve at that temperature
Effect of Temperature on Solubility
• Increasing the temperature of a solution, increases the amount of solute that can be dissolved
• Decreasing the temperature of a solution, causes the solute to recrystallize
Learning Check
1. How many grams of NaCl will dissolve in 100 g of H2O at 90°C?
2. 50 g of KCl is dissolved in 100 g of water at 50°C. Is the solution saturated, unsaturated or supersaturated?
Effect of Pressure on Solubility
• Pressure has a major effect on the solubility of gas-liquid systems
• An increase in pressure increases the solubility of a gas in the liquid
• Polar molecules dissolve other polar molecules and ionic compounds.
• Nonpolar molecules dissolve other nonpolar molecules.
• Alcohols, which have characteristics of both polar & nonpolar, tend to dissolve in both types of solvents, but will not dissolve ionic solids.
“Like dissolves like” – a solvent usually dissolves solutes that have polarities similar to itself
SOLUTES
SOLVENTSWater CCl4 Alcohol
NaCl
I2
C3H7OH
benzene
(nonpolar)
Br2
KNO3
toluene (polar)
Ca(OH)2
methanol
NH3
CO2
polar non polar alcohol
Alcohols are organic, covalent molecules with an –OH group. Alcohol names end with “-ol.”
ionic
polar
non polar
non polar
non polar
ionic
ionic
alcohol
alcohol
and alcohols
and alcohols
and other alcohols
Colligative propertiesColligative properties - the physical changes that result from adding solute to a solvent. Colligative Properties depend on how many solute particles are present as well as the solvent amount, but they do NOT depend on the type of solute particles.
• Boiling Point Elevation• Freezing Point Depression• Osmotic Pressure Increasing• Vapor Pressure Lowering• Conductivity Increasing
More particles/ions = greater change
Learning Check1. Which substance will provide the greatest change in freezing point of water?
A.NaCl B. CaCl2 C. C6H12O6 D. H2O
2. Which of the following reflect colligative properties? (I) A 0.5 m NaBr solution has a higher vapor pressure than a 0.5 m BaCl2 solution.
(II) A 0.5 m NaOH solution freezes at a lower temperature than pure water
(III) Pure water freezes at a higher temperature than pure methanol.
A. only I B. only II C. only III D. I and II E. I and III
2 ions 3 ions 1 particle no change in H2O
2 ions 3 ions
= vapor pressure lowering (more ions lower pressure)
2 ions 0 ions
= freezing point depression
Freezing point is a physical property, not a colligative property
3. A student measured the conductivity in water, of unlabeled liquids, after each added drop. The following graph was produced...
a. Identify the line that represents:– aluminum chloride – water– magnesium chloride – sugar– sodium chloride
b.Which line could
also represent
potassium iodide?
# of Drops
Co
nd
uct
ivity
(µ
s/cm
)
AlCl3, 4 ions
H2O, no change in H2O
MgCl2, 3 ions
C6H12O6, 1 particle
NaCl, 2 ions
H2O
C6H12O6
NaCl
MgCl2
AlCl3
KI, 2 ions = same as NaCl
Solution Composition - Mass Percent
Mass percent – describes a solution’s composition expresses the mass of solute present in a given mass of solution
Mass Percent = mass of solute x 100% mass of solution*
* mass of solution = mass of solute + mass of solvent
Example – A solution is prepared by mixing 1.00g of C2H5OH, with 100.0g of H2O. Calculate the mass percent of ethanol.
Given
mass of solute = 1.00 g
mass of solution = 100.0 g + 1.00 g = 101.0 g
Mass Percent = mass of solute x 100% mass of solution
Mass % = 1.00 g x 100 %101.0 g
Mass % = 0.990 %
Solution Composition – MolarityMolarity – measure of concentration - number of moles of solute per volume of solution in liters
Molarity = moles of solute = mol = M L of solution L
Example – Calculate the molarity of a solution prepared by dissolving 11.5 g NaOH in enough water to make 1.50L solution.
=x __________1
1.50 L NaOH
x ___________mol NaOH
40.00
1
g NaOH
11.5 g NaOH 0.192 M
Ex: Calculate the mass of solid AgCl formed when 1.50L of a 0.100M AgNO3 solution is reacted with excess NaCl.
NaCl + AgNO3 AgCl + NaNO3
1.50 L0.100 M
? g
1.50 L AgNO3 x ______________ L AgNO3
mol AgNO30.100
1 x ____________
mol AgNO3
mol AgCl
1
1
mol AgCl
g AgCl
1
x ____________143.32 = 21.5 g
Example – How many moles of Ag+ ions are present in 25mL of a 0.75M Ag2SO4 solution?
Ag2SO4 2 Ag+1 + SO4-2
25 mL Ag2SO4 L Ag2SO4
mL Ag2SO41000
1 x _____________ x ______________ L Ag2SO4
mol Ag2SO4
1
0.75 x ______________ mol Ag2SO4
mol Ag+12
1=
0.038 mol Ag+1
Learning check
Calculate the molarity of a solution prepared by dissolving 25.6 g NaC2H3O2 in enough water to make 200.0 mL solution.
Standard Solution• Standard Solution – a solution whose
concentration is accurately known
Example – A chemist needs 1.0 L of a 0.200M K2Cr2O7 solution. How much solid K2Cr2O7 must be weighed out to make this solution?
x ______________g K2Cr2O7
mol K2Cr2O7
294.20
1
x ________________mol K2Cr2O7
1
0.200
L K2Cr2O7
1.0 L K2Cr2O7 =
59 g K2Cr2O7
DilutionDilution – process of adding more solvent to a solutionMoles of solute before dilution = Moles of solute after dilution
M1V1 = M2V2
Example: What volume of 16M H2SO4 must be used to prepare 1.5L of a 0.10M H2SO4 solution?
Given
V1 = ?
M1 = 16 M
V2 = 1.5 L
M2 = 0.10 M
V1 = M2V2
M1
_____ V1 = (0.10 M)(1.5 L)____________16 M
V1 = 0.0094 L
Given
V1 = 500.0 mL
M1 = 1.00 M
M2 = 17.5 M
V2 = ?
V2 = M1V1
M2
_____ V2 = (1.00 M)(500.0 mL)_______________17.5 M
V2 = 28.6 mL
Example: Prepare 500.0mL of 1.00 M HC2H3O2 from a 17.5 M stock solution. What volume of the stock solution is required?
Learning Check
Notes-Acids and Bases
Acids and Bases
Arrhenius ACIDS – produces hydrogen ions in aqueous solutions, sour taste, low pH, and the fact that they turn litmus paper red
HCl (aq) H+ (aq) + Cl- (aq)
Arrhenius BASES – produces hydroxide ions in aqueous solutions, bitter taste, slippery feel, high pH, and the fact that they turn litmus paper blue
NaOH (aq) Na+ (aq) + OH- (aq)
Arrhenius definition – limits the concept of a base
Bronsted – Lowry definition – gives a broader definition of a base Bronsted – Lowry ACID – a proton (H+) donor Bronsted – Lowry BASE – a proton (H+) acceptor
General Reaction –
HA (aq) + H2O (l) H3O+ (aq) + A- (aq)
Acid Base Conjugate Conjugate Acid Base
Conjugate Base – everything that remains of the acid molecule after a proton is lost
Conjugate Acid – the base with the transferred proton (H+)Conjugate Acid – Base Pair – two substances related to
each other by the donating and accepting of a single proton
proton donor
proton acceptor
Examples: Finish each equation and identify each member of the conjugate acid –base pair.
H2SO4 (aq) + H2O (l) HSO4-1
(aq) + H3O+ (aq)
Acid Base Conjugate Base
Conjugate Acid
CO32- (aq) + H2O (l) HCO3
-1(aq) + OH-
(aq)
Base Acid Conjugate Acid
Conjugate Base
The hydronium ion, H3O+, forms when water behaves as a base. This happens when the two unshared pairs of electrons on O bond covalently with the H+.
Learning checkWrite the conjugate ACID
a.NH3
b.HCO3-1
Write the conjugate BASE
a.H3PO4
b.HBr
Finish each equation and identify each member of the conjugate acid –base pair.
a. H2SO3 (aq) + H2O (l)
b. SO4-2
(aq) + H2O (l)
Water as an Acid and a Base
Amphoteric – a substance that can behave as either an acid or a base
- water is the most common amphoteric substance
Ionization of Water –
H2O (l) + H2O (l) H3O+ (aq) + OH- (aq)
In the shorthand form:
H2O (l) H+ (aq) + OH- (aq)
Ion-product constant – Kw refers to the ionization of water
Kw = [H+][OH-]
At 25C, Kw = [H+][OH-] = [1.0 x 10-7] [1.0 x 10-7] = 1.0 x 10-14
If [H+] increases, the [OH-] decreases, so the products of the two is still 1.0 x 10-14.
There are three possible situations –1. A neutral solution, where [H+] = [OH-]2. An acidic solution, where [H+] [OH-]3. A basic solution, where [H+] [OH-]
[ ] = concentration[H+] = hydrogen ion concentration in M[OH-] = hydroxide ion concentration in M
Example: Calculate [H+] or [OH-] as required for each of the following solutions at 25C, for each solution state whether it is neutral, acidic, or basic.
a. 1.0 x 10-5 M OH- b. 10.0 M H+
Kw = [H+][OH-]
1 x 10-14 = [H+][1.0 x 10-5 M]
[H+] = 1.0 x 10-9 M
BASIC
Kw = [H+][OH-]
1 x 10-14 = [10.0 M][OH-]
[OH-] = 1.00 x 10-15 M
ACIDIC
pH scalepH scale – because the [H+] in an aqueous solution is
typically small, logarithms are used to express solution acidity
pH = -log [H+] pOH = -log [OH-]
Graphing calculator Non graphing calculator1. Press the +/- key 1. Enter the [H+]2. Press the log key 2. Press the log key3. Enter the [H+] 3. Press the +/- key
Significant Figure Rule – The number of places to the right of the decimal for a log must be equal to the number of significant figures in the original number.
pH pH ScalScal
ee
Example – Calculate the pH or pOH
a. [H+] = 5.9 x 10-9 M b. [OH-] = 2.4 x 10-6 M
pH = - log [H+]
pH = - log (5.9 x 10-9 M)
pH = 8.23
pOH = - log [OH-]
pOH = - log (2.4 x 10-6 M)
pOH = 5.62
Since Kw = [H+][OH-] = 1.0 x 10-14 ,
pH + pOH = 14.00
Example - The pH of blood is about 7.4. What is the pOH of blood?
pH + pOH =14.00
7.4 + pOH = 14.00
pOH = 6.6
In order to calculate the concentration from the pH or pOH,
[H+] = 10-pH [OH-] = 10-pOH
Graphing calculator Non-graphing calculator1. Press the 2nd 1. Enter the pH
function, then log 2. Press the +/- key2. Press the +/- key 3. Press the
inverse3. Enter the pH log key
Example - The pH of a human blood sample was measured to be 7.41. What is the [H+] in blood?
[H+] = 10-pH
[H+] = 10-7.41
[H+] = 3.9 x 10-8 M
Example – The pOH of the water in a fish tank is found to be 6.59. What is the [H+] for this water?
[OH-] = 10-pOH
[OH-] = 10-6.59
[OH-] = 2.6 x 10-7 M
Kw = [H+][OH-]
1 x 10-14 = [H+][2.6 x 10-7 M]
[H+] = 3.8 x 10-8 M
Learning check
• Determine the pH of a solution with a hydrogen ion concentration of 3.2 x10-12 M.
• What is the [OH-] concentration of a solution with a hydrogen ion concentration of 8.9x10-4M?
• What is the pH of a solution with a hydroxide ion concentration of 5.7x10-10 M?
How Do We Measure pH?
• For less accurate measurements, one can use– Litmus paper
• “Red” paper turns blue above ~pH = 8
• “Blue” paper turns red below ~pH = 5
– An indicator
How Do We Measure pH?
For more accurate measurements, one uses a pH meter, which measures the voltage in the solution.
Strong Acids
• seven strong acids are HCl, HBr, HI, HNO3, H2SO4, HClO3, and HClO4.
• These are, by definition, strong electrolytes and exist totally as ions in aqueous solution.
Strong Bases
• Strong bases are the soluble hydroxides, which are the alkali metal and heavier alkaline earth metal hydroxides (Ca2+, Sr2+, and Ba2+).
• Again, these substances dissociate completely in aqueous solution, strong electrolytes
Strong, Weak, or Nonelectrolyte• Electrolytes are substances which, when dissolved in water, break up into
cations (plus-charged ions) and anions (minus-charged ions). We say they ionize. Strong electrolytes ionize completely (100%), while weak electrolytes ionize only partially (usually on the order of 1–10%). The ions in an electrolyte can be used to complete an electric circuit and power a bulb.
• Strong electrolytes fall into three categories: strong acids, strong bases, and soluble salts.
• The weak electrolytes include weak acids, weak bases and insoluble salts.
• Molecules are nonelectrolytes.Substance Classification - Strong acid, weak
acid, strong base, weak base, soluble salt, insoluble salt, molecule
Strong electrolyte, weak electrolyte, nonelectrolyte
sodium
hydroxide
acetic acid
potassium
nitrate
hydrobromic
acid
silver chloride
Carbon dioxide
strong base strong electrolyte
weak acid weak electrolyte
soluble salt strong electrolyte
strong acid strong electrolyte
insoluble salt weak electrolyte
molecule nonelectrolyte
Learning checkSubstance Classification - Strong
acid, weak acid, strong base, weak base, soluble salt, insoluble salt, molecule
Strong electrolyte, weak electrolyte, nonelectrolyte
chloric acid
barium carbonate
nitric acid
sulfurous acid
strontium sulfate
ethanol
octane (gasoline)
Titration
A known concentration of base (or acid) is slowly added to a solution of acid (or base).
Titration
A pH meter or indicators are used to determine when the solution has reached the equivalence point, at which the stoichiometric amount of acid equals that of base.
Titration of a Strong Acid with a Strong Base
From the start of the titration to near the equivalence point, the pH goes up slowly.
Titration of a Strong Acid with a Strong Base
Just before and after the equivalence point, the pH increases rapidly.
Titration of a Strong Acid with a Strong Base
At the equivalence point, moles acid = moles base, and the solution contains only water and the salt from the cation of the base and the anion of the acid.
Titration of a Strong Acid with a Strong Base
As more base is added, the increase in pH again levels off.
Neutralization
Neutralization Reaction =
Acid + Base Salt + Water
Salt – ionic compound containing a positive ion other than H+ and a negative ion other than OH-
Buffered solutions – resists a change in its pH even when a strong acid or base is added to it
- A solution is buffered in the presence of a weak acid and its conjugate base
pH and pOH Calculations
H + O H -
pH pO H
[O H -] = 1 x 10 - 1 4
[H + ]
[H + ] = 1 x 10 - 1 4
[O H -]
p O H = 14 - p H
p H = 14 - p O H
pOH
= -l
og[O
H- ]
pH =
-log
[H+
]
[OH
- ] = 1
0-pO
H
[H+
] = 1
0-pH