types of chemical reactions and solution stoichiometry chapter 4 notes west valley high school ap...
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Types of Chemical Reactions
and Solution Stoichiometry
Chapter 4 Notes
West Valley High School
AP ChemistryMr. Mata
Classification of MatterSolutions are homogeneous mixtures
SoluteA solute is the dissolved substance in a solution.
A solvent is the dissolving medium in a solution.
Solvent
Salt in salt water Sugar in soda drinks
Carbon dioxide in soda drinks
Water in salt water Water in soda
Saturation of Solutions A solution that contains the maximum
amount of solute that may be dissolved under existing conditions is saturated.
A solution that contains less solute than a saturated solution under existing conditions is unsaturated.
A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.
The ammeter measures the flow of electrons (current) through the circuit.
If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting.
Electrolytes vs. Nonelectrolytes
An electrolyte is:
A substance whose aqueous solution conducts an electric current.
A nonelectrolyte is:
A substance whose aqueous solution does not conduct an electric current.
Try to classify the following substances as electrolytes or nonelectrolytes…
Definition of Electrolytes and Nonelectrolytes
1.Pure water2.Tap water3.Sugar solution4.Sodium chloride solution5.Hydrochloric acid solution6.Lactic acid solution7.Ethyl alcohol solution8.Pure, solid sodium chloride
Electrolytes?
ELECTROLYTES: NONELECTROLYTES:
Tap water (weak)
NaCl solution
HCl solution
Lactate solution (weak)
Pure water
Sugar solution
Ethanol solution
Pure, solid NaCl
But why do some compounds conduct electricity insolution while others do not…?
Answers…
Ionic CompoundsDissociate
NaCl(s)
AgNO3(s)
MgCl2(s)
Na2SO4(s)
AlCl3(s)
Na+(aq) + Cl-(aq)
Ag+(aq) + NO3-(aq)
Mg2+(aq) + 2 Cl-(aq)
2 Na+(aq) + SO42-
(aq)Al3+(aq) + 3 Cl-(aq)
The reason for this is the polar nature of the water molecule…
Positive ions associate with the negative end of the water dipole (oxygen).Negative ions associate with the positive end of the water dipole (hydrogen).
Ions tend to stay in solution where they canconduct a current rather than re-forming a solid.
Covalent acids form ions in solution, with the help of the water molecules.
For instance, hydrogen chloride molecules,which are polar, give up their hydrogens towater, forming chloride ions (Cl-) and hydronium ions (H3O+).
Some covalent compounds IONIZE in solution
Other examples of strong acids include:
Sulfuric acid, H2SO4
Nitric acid, HNO3
Hydriodic acid, HI Perchloric acid, HClO4
Strong acids such as HCl are completelyionized in solution.
Many of these weaker acids are “organic” acidsthat contain a “carboxyl” group.
The carboxyl group does not easily give up itshydrogen.
Weak acids such as lactic
acid usually ionize less than 5% of the time.
Other organic acids and their sources include:
o Citric acid – citrus fruito Malic acid – appleso Butyric acid – rancid buttero Amino acids – proteino Nucleic acids – DNA and RNAo Ascorbic acid – Vitamin C
This is an enormous group of compounds; these are only a few examples.
Because of the carboxyl group, organic acids are
sometimes called “carboxylic acids”.
Sugar (sucrose – C12H22O11),
and ethanol (ethyl alcohol – C2H5OH) do notionize - That is why they are nonelectrolytes!
However, most covalent compounds do not ionize
at all in solution.
Molarity
The concentration of a solution measured in moles of solute per liter of solution.
mol = M L
Preparation of Molar Solutions
Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of 0.500 M NaCl solution?
Step #1: Ask “How Much?” (What volume to prepare?)
1.500 L
Step #2: Ask “How Strong?” (What molarity?)
0.500 mol
1 L
Step #3: Ask “What does it weigh?” (Molar mass is?)
58.44 g
1 mol= 43.8 g
Serial DilutionIt is not practical to keep solutions of many different concentrations on hand, so chemists prepare more dilute solutions from a more concentrated “stock” solution.
Serial Dilution
Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution?
MstockVstock = MdiluteVdilute
(11.6 M)(x Liters) = (3.0 M)(0.250 Liters)
x Liters = (3.0 M)(0.250 Liters) 11.6 M
= 0.065 L
Single Replacement Reactions
Replacement of:
Metals by another metal Hydrogen in water by a metal Hydrogen in an acid by a metal Halogens by more active halogens
A + BX AX + B
BX + Y BY + X
The Activity Series of the Metals
Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold
Metals can replace other metalsprovided that they are above themetal that they are trying to replace.
Metals above hydrogen can replace hydrogen in acids.
Metals from sodium upward canreplace hydrogen in water
The Activity Series of the Halogens
Fluorine Chlorine Bromine Iodine
Halogens can replace other halogens in compounds, providedthat they are above the halogenthat they are trying to replace.
2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)
MgCl2(s) + Br2(g) ???No Reaction
???
Double Replacement Reactions
The ions of two compounds exchange places in anaqueous solution to form two new compounds.
AX + BY AY + BX
One of the compounds formed is usually a precipitate (an insoluble solid), an insoluble gas that bubbles out of solution, or a molecular compound, usually water.
Double replacement forming a precipitate…
Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)
Pb2+(aq) + 2 NO3-(aq) + 2 K+(aq) +2 I-(aq) PbI2(s) + 2K+(aq) + 2
NO3-(aq)
Pb2+(aq) + 2 I-(aq) PbI2(s)
Double replacement (ionic) equation
Complete ionic equation shows compounds as aqueous ions
Net ionic equation eliminates the spectator ions
Solubility Rules – Mostly Soluble
Ion Solubility
Exceptions
NO3- Soluble None
ClO4- Soluble None
Na+ Soluble None
K+ Soluble None
NH4+ Soluble None
Cl-, I- Soluble Pb2+, Ag+, Hg22+
SO42- Soluble Ca2+, Ba2+, Sr2+, Pb2+, Ag+,
Hg2+
Solubility Rules – Mostly Insoluble
Ion Solubility
Exceptions
CO32- Insolubl
eGroup IA and NH4
+
PO43- Insolubl
eGroup IA and NH4
+
OH- Insoluble
Group IA and Ca2+, Ba2+, Sr2+
S2- Insoluble
Groups IA, IIA, and NH4+
Oxidation and Reduction (Redox)
Electrons are transferred
Spontaneous redox rxns can transfer energy
Electrons (electricity) Heat
Non-spontaneous redox rxns can be made to happen with electricity
Oxidation and Reduction
Gain Electrons = Reduction
An old memory device for oxidation and reduction goes like this… LEO says GER
Lose Electrons = Oxidation
Oxidation Reduction Reactions(Redox)
11
2
00
22
ClNaClNaEach sodium atom loses one electron:
Each chlorine atom gains one electron:
eNaNa10
10 CleCl
LEO says GER :
eNaNa10
Lose Electrons = Oxidation
Sodium is oxidized
Gain Electrons = Reduction
10 CleCl Chlorine is reduced
Rules for Assigning Oxidation Numbers
Rules 1 & 21. The oxidation number of any
uncombined element is zero
2. The oxidation number of a monatomic ion equals its charge
11
2
00
22
ClNaClNa
Rules for Assigning Oxidation Numbers
Rules 3 & 4
3. The oxidation number of oxygen in compounds is -24. The oxidation number of hydrogen in compounds is +1
2
2
1
OH
Rules for Assigning Oxidation Number Rule 5
5. The sum of the oxidation numbers in the formula of a compound is 02
2
1
OH2(+1) + (-2) = 0 H O
2
122
)(
HOCa(+2) + 2(-2) + 2(+1) = 0 Ca O H
Rules for Assigning Oxidation Numbers
Rule 66. The sum of the oxidation numbers in the formula of a polyatomic ion is equal to its charge
3
2?
ONX + 3(-2) = -1N O
24
2?
OS
X = +5 X = +6
X + 4(-2) = -2S O
Reducing Agents and Oxidizing Agents
The substance reduced is the oxidizing agent The substance oxidized is the reducing agent
eNaNa10
10 CleCl
Sodium is oxidized – it is the reducing agent
Chlorine is reduced – it is the oxidizing agent
Trends in Oxidation and Reduction
Active metals: Lose electrons easily Are easily oxidized Are strong reducing agents
Active nonmetals: Gain electrons easily Are easily reduced Are strong oxidizing agents
Redox Reaction Prediction #1
Important Oxidizers
Formed in reaction
MnO4- (acid solution)
MnO4- (basic solution)
MnO2 (acid solution)
Cr2O72- (acid)
CrO42-
HNO3, concentrated
HNO3, dilute
H2SO4, hot conc
Metallic IonsFree Halogens
HClO4
Na2O2
H2O2
Mn(II)MnO2
Mn(II)Cr(III)Cr(III)NO2
NOSO2
Metallous IonsHalide ionsCl-
OH-
O2
Redox Reaction Prediction #2
Important Reducers Formed in reaction
Halide IonsFree MetalsMetalous IonsNitrite IonsSulfite IonsFree Halogens (dil, basic
sol)Free Halogens (conc, basic
sol)C2O4
2-
HalogensMetal IonsMetallic ionsNitrate IonsSO42-Hypohalite ionsHalate ionsCO2
Not All Reactions are Redox Reactions
Reactions in which there has been no change in oxidation number are not redox rxns.
Examples:
)()()()( 3
2511111
3
251
aqONNasClAgaqClNaaqONAg
)()()()(22
2
1
4
26
2
1
4
26
2
1121
lOHaqOSNaaqOSHaqHONa