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Types of Chemical Types of Chemical ReactionsReactions
and Solution and Solution StoichiometryStoichiometry
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Classification of MatterClassification of MatterSolutions are homogeneous mixtures
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SoluteSoluteA solute is the dissolved substance in a solution.
A solvent is the dissolving medium in a solution.
SolvenSolventt
Salt in salt water Sugar in soda drinks
Carbon dioxide in soda drinks
Water in salt water Water in soda
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Saturation of SolutionsSaturation of Solutions A solution that contains the maximum A solution that contains the maximum
amount of solute that may be dissolved amount of solute that may be dissolved under existing conditions is under existing conditions is saturatedsaturated. .
A solution that contains less solute than A solution that contains less solute than a saturated solution under existing a saturated solution under existing conditions is conditions is unsaturatedunsaturated. .
A solution that contains more dissolved A solution that contains more dissolved solute than a saturated solution under solute than a saturated solution under the same conditions is the same conditions is supersaturatedsupersaturated..
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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. Electrolytes vs. NonelectrolytesNonelectrolytes
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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 Definition of Electrolytes and NonelectrolytesNonelectrolytes
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1.Pure water 2.Tap water 3.Sugar solution 4.Sodium chloride solution 5.Hydrochloric acid solution 6.Lactic acid solution 7.Ethyl alcohol solution 8.Pure, solid sodium chloride
Electrolytes?Electrolytes?
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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 in solution while others do not…?
Answers…Answers…
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Ionic Compounds DissociateIonic Compounds Dissociate
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)
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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.
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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 to water, forming chloride ions (Cl-) and hydronium ions (H3O+).
Some covalent compounds IONIZE in solution
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Other examples of strong acids include:
Sulfuric acid, H2SO4
Nitric acid, HNO3
Hydriodic acid, HI Perchloric acid, HClO4
Hydrobromic acid, HBr Chloric acid, HClO3
Periodic acid, HIO4
Strong acids such as HCl are completelyionized in solution.
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Many of these weaker acids are “organic” acids that contain a “carboxyl” group.
The carboxyl group does not easily give up its hydrogen.
Weak acids such as lactic
acid usually ionize less than 5% of the time.
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Other organic acids and their sources include:
o Citric acid – citrus fruit o Malic acid – apples o Butyric acid – rancid butter o Amino acids – protein o Nucleic acids – DNA and RNA o 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”.
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Sugar (sucrose – C12H22O11),
and ethanol (ethyl alcohol – C2H5OH) do not ionize - That is why they are nonelectrolytes!
However, most covalent compounds do not ionize
at all in solution.
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MolarityMolarity
The concentration of a solution measured in moles of solute per liter of solution.
mol = M L
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Preparation of Molar Preparation of Molar SolutionsSolutions
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
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Serial DilutionSerial Dilution
It is not practical to keep solutions of many different concentrations on hand, so chemists prepare more dilute solutions from a more concentrated “stock” solution.
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
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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
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The Activity Series of the Metals
Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Hydrogen Bismuth Copper Mercury Silver Platinum Gold
Metals can replace other metals provided that they are above the metal that they are trying to replace.
Metals above hydrogen can replace hydrogen in acids.
Metals from sodium upward can replace hydrogen in water
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The Activity Series of the Halogens
Fluorine Chlorine Bromine Iodine
Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace.
2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)
MgCl2(s) + Br2(g) ???No Reaction
???
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Double Replacement Reactions
The ions of two compounds exchange places in an aqueous 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.
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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)
PbPb2+2+(aq) + 2 I(aq) + 2 I--(aq) (aq) PbIPbI22(s)(s)
Double replacement (ionic) equation
Complete ionic equation shows compounds as aqueous ions
Net ionic equation eliminates the spectator ions
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Solubility Rules – Mostly Solubility Rules – Mostly SolubleSoluble
Solubility Rules – Mostly Solubility Rules – Mostly SolubleSolubleIonIon SolubilitSolubilit
yyExceptionsExceptions
NONO33-- SolubleSoluble NoneNone
ClOClO44-- SolubleSoluble NoneNone
NaNa++ SolubleSoluble NoneNone
KK++ SolubleSoluble NoneNone
NHNH44++ SolubleSoluble NoneNone
ClCl--, I, I-- SolubleSoluble PbPb2+2+, Ag, Ag++, Hg, Hg222+2+
SOSO442-2- SolubleSoluble CaCa2+2+, Ba, Ba2+2+, Sr, Sr2+2+, Pb, Pb2+2+, Ag, Ag++, ,
HgHg2+2+
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Solubility Rules – Mostly Solubility Rules – Mostly InsolubleInsoluble
IonIon SolubilitSolubility y
ExceptionsExceptions
COCO332-2- InsolubleInsoluble Group IA and NHGroup IA and NH44
++
POPO443-3- InsolubleInsoluble Group IA and NHGroup IA and NH44
++
OHOH-- InsolubleInsoluble Group IA and CaGroup IA and Ca2+2+, Ba, Ba2+2+, , SrSr2+2+
SS2-2- InsolubleInsoluble Groups IA, IIA, and NHGroups IA, IIA, and NH44++
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Oxidation and Reduction (Redox)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
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Oxidation and ReductionOxidation and Reduction
GGainain EElectronslectrons = = RReductioneduction
An old memory device for An old memory device for oxidation and reduction goes oxidation and reduction goes like this…like this… LEOLEO says says GERGER
LLoseose EElectronslectrons = = OOxidationxidation
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Oxidation Reduction ReactionsOxidation Reduction Reactions(Redox)(Redox)
11
2
00
22
ClNaClNaEach sodium atom loses one electron:
Each chlorine atom gains one electron:
eNaNa10
10 CleCl
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LEO says GERLEO says GER : :
eNaNa10
Lose Electrons = Oxidation
Sodium is oxidized
Gain Electrons = Reduction
10 CleCl Chlorine is reduced
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Rules for Assigning Oxidation Rules for Assigning Oxidation NumbersNumbers
Rules 1 & 2Rules 1 & 2
1. 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
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Rules for Assigning Oxidation Rules for Assigning Oxidation NumbersNumbers
Rules 3 & 4Rules 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
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Rules for Assigning Oxidation Rules for Assigning Oxidation Number Rule 5Number 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
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Rules for Assigning Oxidation Rules for Assigning Oxidation NumbersNumbers
Rule 6Rule 66. The sum of the oxidation numbers in the formula of a polyatomic ion is equal to its charge
3
2?
ONX + 3(-2) = -1 N O
24
2?
OS
X = +5 X = +6
X + 4(-2) = -2 S O
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Reducing Agents and Oxidizing Reducing Agents and Oxidizing AgentsAgents
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
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Trends in Oxidation and ReductionTrends 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
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Redox Reaction Prediction #1
Important Oxidizers Formed in reaction
MnO4- (acid
solution) MnO4-
(basic solution) MnO2 (acid solution) Cr2O7
2- (acid) CrO4
2- HNO3, concentrated HNO3, dilute H2SO4, hot conc Metallic Ions
Free Halogens HClO4
Na2O2
H2O2
Mn(II) MnO2
Mn(II) Cr(III) Cr(III) NO2
NO SO2
Metallous Ions Halide ions Cl-
OH-
O2
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Redox Reaction Prediction #2
Important Reducers Formed in reaction
Halide IonsFree MetalsMetalous Ions Nitrite Ions Sulfite IonsFree Halogens (dil, basic sol) Free Halogens (conc, basic sol) C2O4
2-
Halogens Metal Ions Metallic ions Nitrate Ions SO42- Hypohalite ions Halate ions CO2
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Not All Reactions are Redox Not All Reactions are Redox ReactionsReactions
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