Reminder:
•Memorize complex anions and cations
2/14/19
Ch 4:
Solutions: Homogeneous mixtures of two or more substances
•The solvent is present in greatest abundance
•All other substances are solutes
Dissociation: When an ionic substance dissolves in water, the solvent pulls the individual ions
from the crystal and solvates them
•An electrolyte is a substance into ions when dissolved in water
•A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it
does so
•Soluble ionic compounds tend to be electrolytes
•Molecular compounds tend to be nonelectrolytes, except for acids and bases
•Table 4.3 in the Textbook
•Memorize Table 4.1
Ex.) When soluble ionic compounds dissolve, the ions completely separate from each other
- NaCl(s) => Na+(aq) + Cl-(aq)
- Ca(OH)2(s) => Ca2+(aq) + 2OH-(aq)
- Ca3(PO4)2(s) => 3Ca2+(aq) + 2PO43-(aq)
- PbI2(s) => Not soluble
- Fe(OH)3(s) => Not soluble
Electrolytes:
•A strong electrolyte dissociates completely when dissolved in water
- Strong acids
- Strong bases
- Soluble ionic salts (NaCl, KCl, KNO3)
- Memorize Table 4.2
•A weak electrolyte only dissociates partially when dissolved in water
Precipitation Reactions: When one mixes ions that form compounds that are insoluble (as could
be predicted by solubility guidelines), a precipitate is formed
Metathesis (Exchange) Reactions
•Metathesis comes from the Greek word the means “to transpose”
•It appears as though the ions in the reactant compounds exchange, or transpose, ions:
-AgNO3(aq) + KCl(aq) => AgCl(s) + KNO3(aq)
Solution Chemistry:
•It is helpful to pay attention to exactly what species are present in a reaction
mixture (i.e., solid, liquid, gas, aqueous solution)
•If we are to understand reactivity, we must be aware of just what is changing during
the course of a reaction
Molecular Equations:
•The molecular equation lists the reactants and products in their molecular form:
- AgNO3(aq) + KCl(aq) => AgCl(s) + KNO3(aq)
Ionic Equation
•In the ionic equation all strong electrolytes are dissociated into their ions
•This is more accurately reflects the species that are found in the reaction mixture
Net Ionic Equation:
•To form the net ionic equation, cross out anything that doesn’t change from the left
side of the equation to the right
- Look up rules for crossing out
•The only things left in the equation are those things that change during the course of
the reaction
•Those things that didn’t change (and were deleted from the net ionic equation)
are called specter ions
Writing Net Ionic Equations:
•Write a balanced molecular equation
•Dissociate all strong electrolytes
•Cross out anything that remains unchanged from the left to right
•Write the net ionic equation with the species that remain
3 2 3
More Net Ionic Examples
•Molecular
- Pb(NO3)2(aq) + 2K(aq) => PbI2(s) + 2KNO3(aq)
•Ionic
- Pb2+(aq) + 2NO -(aq) + 2K+(aq) +2I-(aq) => PbI (s) + 2K+(aq) + 2NO -(aq)
•Net
- Pb2+(aq) + 2I-(aq) => PbI2(s)
Acids:
•The Swedish physicist and chemist S.A. Arrhenius defined acids as substances
that increase the concentration of H+ when dissolved in water
•Both the Danish chemist J.N. Brønsted and the British chemist T.M. Lowry defined
them as proton donors
•There are only seven strong acids:
- Hydrochloric acid (HCl)
- Hydrobromic acid (HBr)
- Hydroiodic acid (HI)
- Chloric acid (HClO3)
- Perchloric acid (HClO4)
- Nitric acid (HNO3)
- Sulfuric acid (H2SO4)
Strong vs. Weak Acids:
•HCl(aq) + H2O(l) => H3O-(aq) + Cl-(aq)
Strong 100%
•CH3COOH(aq) + H2O(l) => H3O+(aq) + CH3COOH-
(aq) Weak 0-10%
Bases:
•Arrhenius defined bases as substances that increase the concentration of OH-
when dissolved in water
•Brønsted and Lowry defined them as proton acceptor
Base Examples:
•NH3(aq) + H2O(l) => NH4+(aq) + OH-(aq)
•Adding NH3 to water increases the hydroxide ion concentration, so NH3 is a base
Bases:
•The strong bases are soluble metal salts of hydroxide ion:
- Potassium hydroxide (KOH)
- Sodium hydroxide (NaOH)
- Barium hydroxide (Ba(OH)2)
- Caesium hydroxide (CsOH)
- Strontium hydroxide (Sr(OH)2)
- Lithium hydroxide (LiOH)
- Rubidium hydroxide (RbOH)
Acid-Base Reaction:
•In an acid-base reaction, the acid donates a proton (H+) to the base
Neutralization Reaction:
•Generally, when solutions of an acid and a base are combined, the products are a
salt and water:
- CH3COOH(aq) + NaOH(aq) => CH3COONa(aq) + H2O(l)
- Total Ionic: CH3OOH(aq) + Na+(aq) + OH-(aq) => CH3COO-(aq) + Na+(aq) + H2O(l)
- Net Ionic: Ch3COOH(aq) + OH-(aq) => Ch3COO-(aq) + H2O(l)
•When a strong acid reacts with a strong base, the net ionic equation is
- HCl(aq) + NaOH(aq) => NaCl(aq) + H2O(l)
- H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) => Na+(aq) + Cl-(aq) + H2O(l)
- H+(aq) + OH-(aq) => H2O(l)
Gas-Forming Reactions:
•Some metathesis reactions don’t give the product expected
•In this reaction, the expected product (H2CO3) decomposes to give a gaseous
product (CO2)
- CaCO3(aq) + HCl(aq) => CaCl2(aq) +CO2(g) + H2O(l)
•When a carbonate or bicarbonate reacts with an acid, the products are salt,
carbon dioxide, and water:
- NaHCO3(aq) + HBr(aq) => NaBr(aq) + CO2(g) + H2O(l)
•Similarly, when sulfite reacts with an acid, the products are a salt, sulfur dioxiod,
and water:
- SrSO3(s) + 2HI(aq) => SrI2(aq) + SO2(g) + H2O(l)
•Just as in the precious examples, a gas is formed as a product of this reaction
- Na2S(aq) + H2SO4(aq) => Na2SO4(aq) + H2S(g)
Summary:
•Carbonates and Bicarbonates reacts with acid to form CO2 gas
•Sulfites react with acid to form SO2 gas
•Sulfides react with sulfuric acid to form H2S gas
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Oxidation-Reduction Reaction:
•An oxidation occurs when an atom or ion loses electrons
•A reduction occurs when an atom or ion gains electrons
•One cannot occur without the other
•OIL RIG
3
3
-Oxidation Is Loss of e- Reduction Is Gain of e-
Oxidation Numbers:
•To determine if an oxidation-reduction reaction has occurred, we assign an
oxidation number COMPLETE
•Elements in their elemental form have an oxidation number of 0
•The oxidation number of a monatomic ion is the same as its
charge Ex.) O2(g), Ca(s), Ar(g), Fe(s) all have an Ox # of 0
•Nonmetals tend to have negative oxidation numbers, although sine are positive
in certain compounds or ions
-Oxygen has an Ox # of -2, except in the peroxide ion, in which it has an Ox # -
1 and O2 where it has COMPLETE
•The sum of the Ox # in a neutral compound is 0
•The sum of the Ox # in a polyatomic ion is charge on the ion
- Cl(O-2) - => 3(2-) = 6- => +5 +(6-) = -1
- (K+)Mn(O2-)4 => 4(2-) = 8- => +1 +(8-)= -7
Ox # Example:
•What are the Ox #
- Cu = +1
-COMPLETE
•What is the Ox # of Cl
- Cl(O-2) - => 3(2-) = 6- => +5 +(6-) = -1
- HClO4 => 4(2-)= 8 => +1 +(8-) = +7
Using Ox #:
•What is oxidized and what is reduced in the following reaction
- Zn(s) + 2HCl(aq) => ZnCl2(aq) + H2(g)
- First, determine all the Ox #
Reactants: Zn=0, H=+1, Cl=-
1 Products: Zn=+2, H=0, Cl=-
1
- Second, determine what was oxidized and reduced
-Zn0(s) +2H+1Cl-1(aq) => Zn+2 COMPLETE
Displacement Reactions:
•In displacement reactions, ions oxidize an element
•The ions, then, are reduced
•In this reaction, silver ions oxidize copper metal:
- Cu(s) + 2Ag+(aq) => Cu2+(aq) + 2Ag(s)
- Cu2+(aq) + 2Ag(s) ≠> Cu(s) + 2Ag+(aq)
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Molarity:
•Two solutions can contain the same compounds but be quite different because
the proportions of those compounds are different
•Molarity is one way to measure the concentration of a solution:
- Molarity (M) = moles of solution/solution liter
Ex1.) .34 moles of NaCl is dissolved in water to make a final volume of 2.0 L
.17 mol/L or M
Ex2.) What is the molarity of Na,[Na], COMPLETE
Ex3.) What is the Na2SO4, concentration of a solution prepared by dissolving 3.0 g Na2SO4
in water to make a solution having a total volume of 1.5 L?
.014 mol/L or M
Mixing a Solution:
•To create a solution of known molarity, one weighs out a known mass (and,
therefore, number of moles) of the solute
•The solute is added to a volumetric flask, and solvent is added to the line on the neck
of the flask
Dilution:
•The molarity of the new solution can be determined from the equation:
-Moles=M 1 ∙V 1 = M2 ∙V 2
•Where M1 and M2 are the molarity of the concentrated and dilute solutions,
respectively, and V1 and V2 are the volumes of the two solutions
Ex.) 10.0 mL of a 2.00 M solution is diluted to a total volume of 150.0 mL. What is the
concentration of the resulting solution?
.133 M
Titration:
•Titration is an analytical technique in which one can calcite the concentration of a
solute in a solution
Ex.) HCl (aq) + NaOH (aq) => H2O (l) + NaCl (aq)
A 10.00 mL HCl solution was titrated with 15.00 mL of 0.100 M NaOH solution. What is the
concentration of the acid solution?
Moles= M x V = (0.100 M)(0.01500 L) = 0.00150 moles
.00150 moles NaOH x 1 mol HCl/1 mol NaOH =0.00150 mol
HCl M= moles/liters = 0.00150 mol HCl/0.01 L= 0.015 M
