chemical reactions goals: 1.write balanced equations for simple chemical reactions. 2.understand the...
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Chemical ReactionsChemical Reactions
Goals:
1. Write balanced equations for simple chemical reactions.
2. Understand the nature of ionic compounds dissolved in water.
3. Recognize common acids and bases and understand their behavior in aqueous solution.
4. Recognize and write equations for the common types of reactions in aqueous solution and net-ionic equations.
5. Recognize common oxidizing and reducing agents and identify oxidation-reduction reactions.
Chemical ReactionsChemical Reactions
• A stream of chlorine gas is directed onto solid phosphorus.
• The mixture bursts into flame, and a chemical reactions produces liquid phosphorus trichloride.
What are Chemical Equations?What are Chemical Equations?
Depict the kind of reactants and products and their relative amounts in a reaction.
P4 (s) + 6 Cl2 (g) - - - > 4 PCl3 (l)
The numbers in the front are called
stoichiometric coefficients.The letters (s), (g), and (l) are the
physical states of compounds.
reactants products
Chemical EquationsChemical Equations
P4 (s) + 6 Cl2 (g) - - - > 4 PCl3 (l)
This equation means1 molecule of solid phosphorus (P4) reacts with 6 molecules of chlorine gas producing 4 molecules of phosphorus trichloride.
or___ mol of phosphorus reacts with ___ moles of chlorine producing ___ moles of phosphorus trichloride.
What is the Law of What is the Law of Conservation of Matter?Conservation of Matter?
• Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change.
• Because of the principle of the Because of the principle of the conservation of matter, an conservation of matter, an equation must be balanced.equation must be balanced.It must have the same number It must have the same number of atoms of the same kind on of atoms of the same kind on both sides.both sides. Lavoisier, 1788Lavoisier, 1788
Law of Conservation of Law of Conservation of MatterMatter
We must lay it down as an incontestable axiom, that in all the operations of art and nature, nothing is created; an equal quantity of matter exists both before and after the experiment. …. Upon this principle, the whole art of performing chemical experiments depends.– Lavoisier’s Traité Élémentaire de Chimie.
Law of Conservation of Matter Law of Conservation of Matter and Chemical Equationsand Chemical Equations
P4 (s) + 6 Cl2 (g) - - - > 4 PCl3 (l)
• The numbers in front of each formula – stoichiometric coefficients - in a balanced chemical equation are required by the law of conservation of matter.
Students should become familiar with writing and balancing chemical
equations.
6 x 2 = 12 Cl atoms4 x 3 = 12 Cl atoms
4 P atoms 4 P atoms
Write a reaction for Iron reacting with Chlorine producing Iron (III) chloride
Notice the Notice the stoichiometric stoichiometric coefficientscoefficients and the physical and the physical states of the reactants and states of the reactants and
products.products.
Visualizing Chemical Visualizing Chemical ReactionsReactions
• The reaction between reactant A (red) and reactant B (blue) is shown in the diagram:
Based on this diagram, which equation best describes the reaction?
a) A2 + B A2B b) 2 A + B4 2 AB2
c) A2 + 4 B 2 AB2 d) A + B2 AB2
What is an Aqueous What is an Aqueous Solution?Solution?
• Aqueous solution:Aqueous solution: an homogenous mixture where the solvent is water.
KMnOKMnO44 in water in water KK++(aq) + MnO(aq) + MnO44--(aq)(aq)
How can Water be a solvent for How can Water be a solvent for Ionic Compounds?Ionic Compounds?
Water is a polar molecule: it has a ___________ (one side of the molecule is +, the other is -).This is due to the difference in _________________ (the ability of an atom in a molecule to attract electrons to itself) between oxygen and hydrogen.
O is more electronegative than H: O appears partially ________ charged (), and H partially __________ charged (+).
How do we know ions are How do we know ions are present in aqueous present in aqueous
solutions?solutions?The solutions The solutions conduct _______________!!
The The substances that provide ions in an aqueous solution are calledare called ____________________________________..
HCl, CuClHCl, CuCl22, and NaCl are, and NaCl are_____ _________. _____ _________.
What is a Strong Electrolyte?What is a Strong Electrolyte?
They They ionizeionize or or dissociatedissociate completely completely (or nearly so) into (or nearly so) into ionsions..
HCl, CuClHCl, CuCl22, and NaCl are , and NaCl are strong strong electrolytes.electrolytes.
HCl (aq) H+(aq) + Cl-(aq)
What is a Weak Electrolyte?What is a Weak Electrolyte?
Acetic acid ionizes only to a small extent, so it is a
weak electrolyte.weak electrolyte.CH3CO2H(aq)
CH3CO2-(aq) +
H+(aq)
What is a Nonelectrolyte?What is a Nonelectrolyte?
Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes.nonelectrolytes.Examples include:Examples include:
sugarsugarethanolethanol
ethylene glycolethylene glycol
Summary of the Electrolytic Summary of the Electrolytic BehaviorBehavior
of Common of Common Soluble IonicSoluble Ionic and andMolecular CompoundsMolecular Compounds
Strong Weak Electrolyte Electrolyte
Nonelectrolyte
Ionic
Molecular
All
All others
None
Strong acids
None
Weak acidsandWeak bases(NH3)
Which Ionic Compounds are Which Ionic Compounds are Soluble in Water?Soluble in Water?
If one ion from the “Soluble If one ion from the “Soluble Compd.” list is present in a Compd.” list is present in a
compound, the compound is compound, the compound is water soluble.water soluble.
Book Ed 7:
Figure 3.10 (p. 126)
Book Ed 6:
Figure 5.3 (p. 179)
Learn this
table!
Solubility of Ionic Solubility of Ionic CompoundsCompounds
What is an Acid?What is an Acid?
An acid - - -> HAn acid - - -> H++ (in (in water)water)
Some Some strongstrong acidsacids(completely ionized) are:(completely ionized) are:HClHCl hydrochlorichydrochloric
HH22SOSO44 sulfuricsulfuric
HClOHClO44 perchloricperchloric
HNOHNO33 nitricnitric
HNOHNO33
PROTONBecause a hydrogen atom is one proton and one electron, a hydrogen ion (H+) is simply a proton.
What is an Acid?What is an Acid?
An acid ---> HAn acid ---> H++ in water in waterAn acid ---> HAn acid ---> H++ in water in water
HCl(aq) H+(aq) + Cl-(aq)
What is the Hydronium Ion?What is the Hydronium Ion?
HCl
H2O
Cl-
H3O+
hydronium ion
HCl(aq) H+(aq) + Cl-(aq)
Bronsted – Lowry Theory:An acid donates a proton
What is a Weak Acid?What is a Weak Acid?
WEAK ACIDS (only partially WEAK ACIDS (only partially ionizedionized))= weak electrolytes= weak electrolytes
CHCH33COCO22HH acetic acidacetic acid
HH22COCO33 carbonic acidcarbonic acid
HH33POPO44 phosphoric acidphosphoric acidHFHF hydrofluoric acidhydrofluoric acid
CHCH33COCO22H H (aq) H+(aq) + CHCH33COCO22- (aq)
Weak AcidWeak Acid
What is a Base?What is a Base?
Base ---> OHBase ---> OH-- in water in waterBase ---> OHBase ---> OH-- in water in water
NaOH(aq) ---> NaNaOH(aq) ---> Na++(aq) + OH(aq) + OH--
(aq)(aq)
NaOH is NaOH is a a strong strong basebase
HYDROXIDE
How is it that Ammonia, NHHow is it that Ammonia, NH33 is a base?is a base?
Bronsted – Lowry Theory:A base accepts a proton
Acids and BasesAcids and Bases
Students should become familiar with identifying acids and
bases.
Book Ed 7: p. 132
Book Ed 6: p. 187
Representative Trends in Strength of Binary Representative Trends in Strength of Binary Acids (containing only H atoms and a Acids (containing only H atoms and a
nonmetal)nonmetal)
Smaller atom bonded to HShorter bondWeaker acid
Larger atom bonded to HLonger bondStronger acid
Higher electronegativity difference of atoms - more polar bond
baseneutral
weak acid
strong acid
The Bronsted-Lowry TheoryThe Bronsted-Lowry Theory
• 1923 – J. N. Bronsted and T. M. Lowry:
• Acids – a proton (H+) ________.
• Bases – a proton (H+) _________.
HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq)
• A reaction between an acid and a base consists of a proton transfer from an acid to a base.
Conjugate PairsConjugate Pairs• The products of an acid-base reaction are also an acid
and a base. The overall reaction consists of two combinations of acids and bases – conjugates pairs.
CH3COOH + H2O CH3COO- + H3O+
• The acid-base conjugate pairs differs in structure only by a proton (H+):– The conjugate acid of a specie is that specie plus _______.– The conjugate base of a specie is that specie minus
__________.
acid (1) base (2) acid (2)base (1)
Conjugate PairsConjugate Pairs
NH3 + H2O NH4+ + OH-
Ammonia (NH3) acts as a base by accepting a proton from H2O. In the reverse reaction, ammonium ion (NH4
+) acts as acid by losing a proton to OH-.
Amphiprotic – a substance that can act ________ __________________________
acid (2)base (1) acid (1) base (2)
Dual Role of WaterDual Role of Water
• Amphiprotic – a substance that can act either as an acid or a base – like H2O.
pair of e- in bond are kept by O atom
lone pair of e- forms new bond
Water EquilibriumWater Equilibrium
• Self-ionization of water: about 1 water molecule in 500 million transfer a proton to another water molecule:
H2O + H2O H3O+ + OH-
• Water is in equilibrium with a hydronium ion and a hydroxide ion (or using our convention with a hydrogen ion and a hydroxide ion).
H2O H+ + OH-
Water EquilibriumWater Equilibrium• Equilibrium lies far to the left (it is mostly
water molecules). Experimentally determined concentrations of ions (25oC) in molarity (moles per liter) are:
[H+] = [OH-] = 1.0 x 10-7 M (= 0.0000001 M)
• Ion product of water (Kw) – product of the concentrations of H+ and OH-, at 25oC is:
Kw = [H+] [OH-] = (1.0 x 10-7) (1.0 x 10-7) = 1.0 x 10-14
• The ion product relationship applies to all aqueous solutions (acids, bases, salts).
What are Basic Oxides?What are Basic Oxides?(Basic Anhydrides)(Basic Anhydrides)
Metal Metal oxides react with water to form bases
CaO(s) + H2O(liq) -- > Ca(OH)2(aq)
CaO in water. Indicator shows solution is basic.
What are Acidic Oxides?What are Acidic Oxides?(Acidic Anhydrides)(Acidic Anhydrides)
NonmetalNonmetal oxides react with water to form acids
CO2(aq) + H2O(l) ---> H2CO3(aq)
SO3(aq) + H2O(l) ---> H2SO4(aq)
And can come from burning coal and oil.
= ACID RAIN
What is a Net Ionic What is a Net Ionic Equation?Equation?
Mg(s) + 2 HCl(aq) --> HMg(s) + 2 HCl(aq) --> H22(g) + MgCl(g) + MgCl22(aq)(aq)
We really should writeWe really should write
Mg(s) + 2 HMg(s) + 2 H++(aq) + 2 Cl(aq) + 2 Cl--(aq) ---> (aq) ---> HH22(g) + Mg(g) + Mg2+2+(aq) + 2 Cl(aq) + 2 Cl--(aq)(aq)
The two Cl- ions are ____________ IONS____________ IONS — they do not participate (could have used NO3
-).We leave the spectator ions out — to write aNET IONIC EQ:
Mg(s) + 2 H+(aq) ---> H2(g) + Mg2+(aq)
Review in Exp 8: Six bottles experiment
Which Which Types of ReactionsTypes of Reactions occur in occur in Aqueous Solution?Aqueous Solution?
• EXCHANGE REACTIONSEXCHANGE REACTIONSThe anions exchange placesbetween cations:
Precipitation
Acid-base; neutralization
Gas-forming
• OXIDATION-REDUCTION REACTIONSOXIDATION-REDUCTION REACTIONSElectron Transfer.
Driving forceFormation of ________
compound Formation of _____ and ______; proton transfer
Evolution of _____________________
What are Precipitation Reactions?What are Precipitation Reactions?
The “driving force” is the The “driving force” is the formation of an insoluble formation of an insoluble compound — a compound — a precipitateprecipitate..
Pb(NOPb(NO33))22(aq) + 2 KI(aq)(aq) + 2 KI(aq)
-----> 2 KNO-----> 2 KNO33(aq) + PbI(aq) + PbI22(s)(s)
Net ionic equation: Net ionic equation:
Net Ionic EquationNet Ionic Equation
Complete formula equation:Complete formula equation:
Pb(NOPb(NO33))2 2 (aq)(aq) + 2 KI + 2 KI (aq)(aq)
-----> 2 KNO-----> 2 KNO3 3 (aq)(aq) + + PbIPbI2 2 (s)(s)
Ionic equation:
Net ionic equation:Net ionic equation:
What are Acid-Base Reactions?What are Acid-Base Reactions?
• The “driving force” is the formation of water.The “driving force” is the formation of water.
NaOH(aq) + HCl(aq) ---> NaCl(aq) + NaOH(aq) + HCl(aq) ---> NaCl(aq) + HH22O(liq)O(liq)
• Net ionic equationNet ionic equation
OHOH--(aq) + H(aq) + H++(aq) ---> H(aq) ---> H22O(liq)O(liq)
This applies to ALL reactions ofThis applies to ALL reactions of
STRONG STRONG acids and bases.acids and bases.
Acid-Base ReactionsAcid-Base Reactions
Complete formula equation:HCl (aq) + NaOH (aq)
Ionic equation:
Net ionic equation:
products do not have characteristics of acid or base.
For strong acids and bases write the ionic form.
Write the equations for ammonia added to Write the equations for ammonia added to phosphoric acid to make ammonium phosphoric acid to make ammonium
phosphate.phosphate.
Complete formula equation:3 NH3 (aq) + H3PO4 (aq)
Ionic equation:
Net ionic equation:
For weak acids and bases do not write the ionic form.
Acid-Base ReactionsAcid-Base Reactions
• Acid-Base reactions are sometimes called
NEUTRALIZATIONS because the solution is
neither acidic nor basic at the end.
• The other product of Acid-Base reactions is a
SALT, with general formula: MX.
HX + MOH ---> MX + H2O
Mn+ comes from base & Xn- comes from acid
This is one way to make compounds!
Salt Water
What are Gas-Forming Reactions?What are Gas-Forming Reactions?
This is primarily the chemistry of metal carbonates.
CO2 and water ---> H2CO3
H2CO3(aq) + Ca2+ ---> 2 H+(aq) +
CaCO3(s) (limestone)
Adding acid reverses this reaction.
MCO3 + acid ---> CO2 + H2O + salt carbonates carbon dioxide
Gas-Forming ReactionsGas-Forming Reactions
CaCO3(s) + H2SO4(aq) --->
2 CaSO4(s) + H2CO3(aq)
Carbonic acid is unstable and forms CO2 & H2O
H2CO3(aq) ---> CO2+ H2O
(Antacid tablethas citric acid + NaHCO3)
PracticePractice
• Write down the complete formula, ionic, and net ionic equations for:Sulfuric acid reacts with calcium carbonate.
Students should become familiar with writing ionic and net
equations.
Gas-Forming ReactionsGas-Forming Reactions
Book Ed 7. p. 140
Book Ed 6: p. 194
Students should become familiar with identifying the several types of
reactions and predicting products of the reactions.
Redox ReactionsRedox Reactions
FuelsFuelsFuelsFuels
CorrosionCorrosionCorrosionCorrosion
BatteriesBatteriesBatteriesBatteries
Manufacturing metalsManufacturing metalsManufacturing metalsManufacturing metals
PhotosynthesisPhotosynthesis
6 CO2 + 6 H2O C6H12O6 + 6 O2
Combustion, respiration/metabolism
C6H12O6 + 6 O2 6 CO2 + 6 H2O
Oxidation and ReductionOxidation and Reduction
• Oxidation is a ________________.• Reduction is a __________________.
LEO says GER
Mg + Cl2 Mg2+ + 2 Cl-
Mg atom _____________; it is __________.
Cl atoms _____________; Cl2 is ___________.
What are Redox Reactions?What are Redox Reactions?
• An oxidation-reduction reaction - must always have both an oxidation and a reduction.Oxidation process – the oxidation number of one or more elements ___________.Reduction process – and the oxidation number of one or more elements _________.
Mg (s) + Cu2+(aq) Mg2+
(aq) + Cu (s)
Half- ReactionsHalf- Reactions
• A redox reaction is two half-reactions that occur simultaneously.
Mg (s) + Cu2+(aq) Mg2+
(aq) + Cu (s)
0 +2 +2 0
Oxidation half-reaction:Mg atoms lose 2 e-
Reduction half-reaction:Cu2+ ions gain 2-
Mg (s) Mg2+(aq) + _____
Cu2+(aq) + _____ Cu (s)
oxidation
reduction
Hydrogen-Oxygen Fuel CellHydrogen-Oxygen Fuel Cell
Hydrogen-Oxygen Fuel CellHydrogen-Oxygen Fuel Cell
• Fuel cellFuel cell - reactants are supplied - reactants are supplied
continuously from an external continuously from an external
source.source.• Cars can use electricity generated Cars can use electricity generated
by Hby H22/O/O22 fuel cells. fuel cells.
• HH22 carried in tanks or generated carried in tanks or generated
from hydrocarbons– (if possible from hydrocarbons– (if possible
solar)solar)
2 H2 + O2 2 H2O
2 H2 4 H+ + 4 e-
O2 + 4 e- 2 O-2
4 H+ + 2 O-2 2 H2O
2 H2 + O2 2 H2O
Identifying Redox ReactionsIdentifying Redox Reactions
• Look for a change in the oxidation number of an element in the course of the reaction.
What are oxidation numbers?
Is the charge an atom has, or appears to have, as determined by the following guidelines for assigning oxidation numbers.Students should become familiar
with assigning OXIDATION NUMBERS – learn the rules.
(Page 200)
Oxidation Numbers in HF: Animation
Follow the Follow the rulesrules for Oxidation Numbers for Oxidation Numbers1. Each atom in a pure element has an oxidation
number of zero. Cu, I2, S8.2. For monoatomic ions, the oxidation number is equal
to the charge on the ion. NaBr, MgBr2.3. Fluorine always has an oxidation number of -1 in
compounds with all other elements.4. Cl, Br, and I always have oxidation number of -1 in
compounds, except when combined with oxygen or fluorine. NaCl, ClO-.
5. The oxidation number of H is +1 and of O is -2 in most compounds. Exceptions: H in a binary compound with a metal, CaH2. O in peroxides can have an oxidation number of -1, H2O2.
6. The algebraic sum of the oxidation numbers for atoms in a neutral compound must be zero; in a polyatomic ion, the sum must be equal to the ion charge. HClO4
Give the Oxidation Number of each Element Give the Oxidation Number of each Element in the following:in the following:
Br2
Na2SO4
CaH2
Fe2O3
P4
H2O2
KMnO4
What is Oxidizing Agent?What is Oxidizing Agent?What is Reducing Agent?What is Reducing Agent?
• OXIDIZING AGENT:The substance that accepts electrons in an oxidation-reduction reaction and gets reduced.
• REDUCING AGENT:The substance that donates electrons in an oxidation-reduction reaction and gets oxidized.
Oxidizing and Reducing AgentsOxidizing and Reducing Agents
K (s) + H2O (l) KOH (aq) + H2 (g)2 2 2
Common Oxidizing and Common Oxidizing and Reducing Agents (Table 5.4, p. Reducing Agents (Table 5.4, p.
203)203)
HNOHNO33 is an is an
oxidizing agentoxidizing agent
2 K + 2 H2 K + 2 H22O --> 2 KOH + HO --> 2 KOH + H22
MetalsMetals (Na, (Na, K, Mg, Fe) K, Mg, Fe) are are reducing reducing agentsagents
Metals Metals (Cu) (Cu) are reducing are reducing agentsagents
Cu + HNOCu + HNO33 --> Cu --> Cu2+2+ + NO + NO22
Students should be familiar with common oxidizing and reducing
agents.
O2, F2, Cl2, Br2, I2, Cr2O2-, MnO4
- H2, Na, K, Fe, Al, C
• Oxygen - Oxidizes coal in electric power plants, gasoline in automobiles, “burns” the food we eat.
• Potassium dichromate - Lab: aldehydes to ketones; ethanol to acetaldehyde.
• Potassium permanganate - Lab: color test for many oxidizable substances (purple color disappears).
• Halogens and Peroxides– Antiseptics – substance applied to living tissue to kill
microorganisms or prevent their growth: Iodine, Hydrogen peroxide (3% sol), Benzoyl peroxide.
– Disinfectants – substance that is applied to nonliving tissue to kill microorganisms: Chlorine from [Ca(OCl)2].
Oxidizing AgentsOxidizing Agents
MnO4- + 5 Fe2+ + 8 H+ Mn2+ + 5 Fe3+ + 4 H2O
Cr2O72- + 3 C2H5OH + 8 H+ 2 Cr3+ + 3 C2H4O + 7 H2O
acetaldehyde
Reducing AgentsReducing Agents• Carbon - To obtain free metals from their ores.
• Metals - To obtain free metals from their ores.
• Hydrogen - To obtain free metals from their ores and to reduce many kinds chemical compounds.
• Organic Compounds– Hydroquinone: it reduces silver ions in photographic films
– Antioxidants – in food chemistryVitamin C (ascorbic acid) prevents the browning of fruit by inhibiting air oxidation.Vitamin E (tocopherol) - Both vitamins retard oxidation reactions that damage
vital components of living cells.
SnO2 (s) + 8 C (s) Sn (s) + CO2 (g)
Cr2O3 (s) + 2 Al (s) Al2O3 (s) + 2 Cr(s)
WO3 (s) + 3 H2 (g) W (s) + 3 H2O
N2 (g) + 3 H2 (g) 2 NH3 (g)Fe
C6H4(OH)2 (aq) + 2 Ag+ (aq) C6H4O2 (aq) + 2 Ag (s) + 2 H+
RememberRemember
• Go over all the contents of your textbook.
• Practice with examples and with problems at the end of the chapter.
• Practice with OWL tutor.• Work on your assignment for OWL
Chapters 4, 5.• Practice with the quiz on CD of
Chemistry Now.