ch 4 reactions in aqueous solutions. types of equations used to describe reactions in solution...
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CH 4 Reactions in Aqueous Solutions
Types of Equations Used to Describe Reactions in Solution
1. Molecular: overall reaction stoichiometry- not actual forms
MgSO4 (aq) + Na2CO3 (aq) --> MgCO3 (s) + Na2SO4 (aq)
2. Complete Ionic: reactants and products that are strong electrolytes are represented as ions.
Mg2+ + SO42- + 2Na+ + CO3
2- --> MgCO3 (s) + 2Na+ + CO32-
3. Net Ionic: includes only those solution components undergoing a change. Spectator ions not included.
Mg2+ + CO32- --> MgCO3 (s)
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Types of Chemical Reactions Combination (Synthesis) reaction A + B ABDecomposition reactions AB A + BDisplacement reactions AB + C AC + BMetathetical (change of position)
reactions (double-replacement reactions)
AB + CD AD + CBCombustion reactions reactions with oxygen CxHy + nO2 xCO2 + (y/2) H2O04/19/23 3
Combination Reactions (Synthesis): A + B → C
Metals + Oxygen:– Lithium + oxygen →– Magnesium + oxygen →– Gold + oxygen →– Platinum + oxygen →
Remember the diatomicsMetals with multiple charges: choose the one with higher charge; Cu+2 and not Cu+1
Nonmetals + Oxygen (Redox?)Excess carbon with oxygen →Limited amount of carbon with excess of oxygen →Phosphorus + excess oxygen →Phosphorus with limited amount of oxygen →
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Combination Reactions (Synthesis): A + B → C
Metals + nonmetals (Redox?)Cesium metal + iodine →Zinc + sulfur →Magnesium + nitrogen →
Metal Oxides (most are solid) + Water: (Redox?)
Magnesium oxide + water →Lithium oxide + water →Aluminum oxide + water → Iron(III) oxide + water →
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Combination Reactions (Synthesis): A + B → C
Nonmetal Oxides + Water : (Redox?)
solid calcium oxide + water →solid lithium oxide + water →
Can be Redox: 2NO2(g) + H2O (l) → HNO3 (aq) + HNO2(aq)
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Combination Reactions (Synthesis): A + B → C
Metal Oxides + Nonmetal Oxides (Redox?)calcium oxide + silicon dioxide →lithium oxide + tetra phosphorus deca oxide →
Notes: The more electropositive (most metallic) element is always
written firstP4O10; CaO; H2O, CO2
Check Periodic Table
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Decomposition Reactions : C → A + B Reverse of combination (synthesis)
Metallic oxides metal + oxygen
Nonmetallic oxides nonmetal + oxygen
Hydroxide metal oxide + water
Acid nonmetallic oxide + water
Which are Redox and which are not?
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Decomposition Reactions (Special Cases)
Metal carbonates metallic oxide + CO2
Metal bicarbonates: metal oxide + CO2(g) + H2O (l)
Metal sulfite metallic oxide + SO2
Metal chlorate metal chloride + oxygen (O2)
Binary compounds elements
Electrolysis of molten salts (ionic compounds) elements
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Decomposition Reactions : (Special Cases)
Decomposition of peroxides: peroxide water + oxygen (O2)
Ammonium compounds acid + ammonia; the acid may decompose
(NH4)2CO3 (s) 2NH3(g) + CO2(g) + H2O(l)
NH4NO2 (s) N2(g) + 2H2O (l)
NH4NO3(s) N2O (g) + 2H2O(l)
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Types of Equations Used to Describe Reactions in Solution
1. Molecular: overall reaction stoichiometry- not actual forms
MgSO4 (aq) + Na2CO3 (aq) --> MgCO3 (s) + Na2SO4 (aq)
2. Complete Ionic: reactants and products that are strong electrolytes are represented as ions.
Mg2+ + SO42- + 2Na+ + CO3
2- --> MgCO3 (s) + 2Na+ + CO32-
3. Net Ionic: includes only those solution components undergoing a change. Spectator ions not included.
Mg2+ + CO32- --> MgCO3 (s)
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Writing Equations
Write a balanced molecular, ionic and net ionic equations for the following reactions:
1. Solution of silver nitrate was added to a solution of sodium chromate
2. A piece of solid zinc was placed in a solution of Copper(II) chloride
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Single Replacement or Displacement Reactions
A0 + B+C- A+C- + B- ( metals)
A0 + B+C- B+A- + C0 (halogens)
All are Redox
Active metal replaces less active metalActive metal replaces H in water or acidsNonmetal replaces less active nonmetal
Activity series – used to predict RxStandard Reduction Potential Chart and SHE
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Single Replacement Reactions If a < reactive element is combined with a > reactive element in compound form → no Rx
1. Zinc metal reacts with copper (II) sulfate in water solutionMolecular equation:Net Ionic equation :
Redox?
2. zinc metal reacts with hydrochloric acid
3. aluminum metal reacts with sulfuric acid
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Single Replacement Reactions
Write formula and net ionic equations:
sodium metal reacts with cold a water
aluminum reacts with steam
magnesium reacts with hot water
Which metals will replace hydrogen from cold water?
Which metals will replace hydrogen from hot water?
Which metals will replace hydrogen from steam?
Activity series of metals:
http://www.chem.vt.edu/RVGS/ACT/notes/activity_series.html04/19/23 15
Single Replacement Reactions: Halogen Displacement
Write molecular and net ionic equations:
Chlorine gas reacts with aqueous solution with sodium bromide
Activity series:F2 > Cl2 > Br2 > I2
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Double Replacement Reactions orMetathetical Reactions
A+B- + C+D- A+ D- + C+B-
Reactions occur to completion when:Precipitate is producedGas is producedMolecular substance such as H2O, CO2, NH3,
SO2 are produced
Redox or NonRedox ?04/19/23 17
Double Replacement Reactions orMetathetical Reactions
Write the molecular complete ionic
net ionic forms
Aqueous nickel (II) chloride reacts with aqueous sodium hydroxide
Aqueous sodium sulfide reacts with lead (II) nitrate
Aqueous potassium carbonate reacts with barium chloride
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Double Replacement Reactions orMetathetical Reactions
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Predict whether a reaction will occur in each of the following case. If so, write a net ionic equation for the reaction. If no reaction occurs, write NR after arrow.
Al2(SO4)3 + NaOH
K2SO4(aq)+FeBr3(aq)
CdCl2(aq) + (NH4)2S(aq)
Double Replacement: Gas FormationCommon gases formed in DR Rx
S2- + acid → H2S (g)+ salt
CO32- + acid → CO2 (g)+ H2O + salt
SO3- + acid → SO2 (g)+ H2O + salt
NH4+ + OH- + Δ → NH3 g) + H2O + salt
1. Sodium carbonate reacts with hydrochloric acid2. Ammonium chloride reacts with sodium hydroxide3. Magnesium nitride reacts with water 4. Calcium sulfite reacts with hydrobromic acid5. Sodium chloride + sulfuric acid6. Sodium sulfide reacts with hydrochloric acid
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Selective Precipitation
Precipitation reactions allow us to target specific substances, and separate and recover them from a solution.
Example:A solution contains Ca2+, Cu2+, and Pb2+. What
anions can we add, and in what order , to separate and recover each cation?
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Combustion
Write the products and balance the following combustion reaction:
C6H12O6 (s) + O2 →C3H8O3 + O2 →CH3OH + O2
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Acids and Bases: Arrhenius
Acid– Any substance that releases H+ ion in aqueous
solution
Base– Any substance that releases OH- ion in aqueous
solution
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Brønsted-Lowery Acid-Base Definitions
An acid is a substance that donates a proton (H+) to a base
A base is a substance that accepts a proton (H+) from an acid
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conjugate base
conjugate. acid
Brønsted-Lowery Acid-Base Definitions
An acid is a substance that donates a proton (H+) to a base
A base is a substance that accepts a proton (H+) from an acid
Acid-base reactions can be reversible:reactants products or products reactants
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Conjugate acid: ____________
Conjugate base: _________________
Compounds that act as Brönsted Acid and Base
Write equations for the following reactions. Identify the acid, base, conjugated acid and conjugated base:
1. HSO4-(aq) + H2O(l) →
2. HSO4-(aq) + H2O(l) →
3. H2O(l) + H2O(l) →4. HCO3
-1 (aq) + H2O(l)
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Important Acids and Bases
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Strong Acids:
HCl hydrochloric
HBr hydrobromic
HI hydroiodic
HNO3 nitric
H2SO4 sulfuric
HClO4 perchloric
Weak Acid:
CH3CO2H acetic
Strong Bases:
NaOH sodium hydroxide
KOH potassium hydroxide
Ca(OH)2 calcium hydroxide
Weak Base:
NH3 ammonia
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Know the strong Know the strong acids & bases!acids & bases!
Ca(OH)2, Ba(OH)2 and Sr(OH)2
Group IIA, heavy metals)
Ca(OH)2, Ba(OH)2 and Sr(OH)2
Group IIA, heavy metals)
3.2
STRONG acids in water: 100% of acid molecules form ions:
HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
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H3O+ is
hydronium ion
WEAK acids in water: ~5% or less of acid molecules form ions
(acetic, H3PO4, H2CO3)
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Polyprotic Acids: multiple acidic H atoms
H2SO4 H+ + HSO4-
HSO4- H+ + SO4
2-
Not all H’s are acidic: CH3CO2H
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If H3PO4 reacts as an acid, which of the following can it not make?
1. H4PO4+
2. H2PO4-
3. HPO42-
4. PO43-
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Reactions Involving Weak Bases
HCl(aq) + NH3(aq) NH4+(aq) + Cl-(aq)
Net-Ionic Equation:
NH3(aq) + H+(aq) NH4+(aq)
Spectator Ion?
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Acid-Base Reactions: Neutralization
The “driving force” is the formation of water.The “driving force” is the formation of water.NaOH(aq) + HCl(aq) NaOH(aq) + HCl(aq) → → NaCl(aq) + HNaCl(aq) + H22O(liq)O(liq)
Net ionic equationNet ionic equation OHOH--(aq) + H(aq) + H++(aq) (aq) →→ H H22O(liq)O(liq)
““Spectator Ions”? __________________________Spectator Ions”? __________________________
This applies to ALL reactions of STRONG acids This applies to ALL reactions of STRONG acids
and bases.and bases.
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Acid-Base Neutralization RxPolyprotic acids
H2SO4 (SA)or H3PO4 (WA)
H2SO4 : First H+ is ionized completely
H2SO4 → H+ + HSO4 -
1. If base is excess: all H+ form H2O
2. If equimolar acid + base: only 1 H+ ionizes3. Acidic anhydrides (NMO) + Basic anhydrides (MO) :
react with H2O before acid or base
CH3CO2H(aq) + NaOH(aq)
Choose the correct answer:1. CH3CO2H2
+(aq) + NaO(aq)2. CH3CO2
-(aq) + H2O(l) + Na+(aq)3. CH4(g) + CO2(g) + H2O(l)
Complete Ionic equation:
CH3COOH(aq) + OH-(aq) → CH3COO-(aq) + H2O(l)
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HCN(aq) + NH3(aq)
Answer?1. NH4
+(aq) + CN-(aq)
2. H2CN+(aq) + NH2-(aq)
3. C2N2(s) + 3 H2(g)
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Hydrolysis Rx- Reverse NeutralizationSalt + H2O → molecular species
Formation of a weak acid and/or weak baseNH4
+ + Cl- + H2O → H+ + Cl- + NH4OH
NH4Cl : salt from SA (HCl) + WB (NH3 )
Forms acidic solution due to: NH4+> OH-
*Salts of SA + WB → Acidic Solution*Salts of SA + WB → Basic Solution
*Salts of SA + SB → Neutral Solution*Salts of WA + SB → ?? Check Ka and Kb
1. Aqueous potassium fluoride undergoes hydrolysis when placed in water.
2. Sodium chloride and water are mixed together.
3. Ammonium fluoride and water are mixed together.
Oxidation-Reduction Reactions
Redox reactions: involve a transfer of electrons.
Assigning oxidation states to an element in a molecule:
K2CrO4 LiSCN
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LEO GER: Leo the Lion Says GEROIL RIG
Loss of Electrons is OxidationGain of Electrons is Reduction
Oxidation Involves LossReduction Involves Gain
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Determination of Oxidation States
Fe2O3 + 2Al → Al2O3 + 2Fe
Iron (III) gains 3 electrons to become elemental iron.
Elemental aluminum lost 3 electrons to become the aluminum ion.
Write the half reactions:
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N2 H4 + N2O4 → N2 + H2O
The combustion of hydrazine with dinitrogen tetroxide helps to keep the space shuttle in Earth Orbit.
Is it a Redox reaction? Explain.
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Fe2O3 + 2Al → Al2O3 + 2Fe
Iron (III) ion gained electrons. It has been reduced.
The aluminum lost electrons. It has been oxidized.
The oxidizing agent is the species that is reduced (Iron (III)).
The reducing agent is the species that is oxidized (aluminum).
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Rules for Assigning Oxidation States (OS)1. OS of an atom in an element is 0.
Na (s), O2 (g)2. OS of a monatomic ion is the same as its charge.
Na+ OS = +1, Cl- OS = -13. In its covalent compounds with nonmetals, hydrogen is
assigned an OS of +1. HCl, NH3, H2O.
4. Oxygen is assigned an OS of -2 in its covalent compounds.
CO, CO2, SO2, SO3
The exception to this rules occurs in peroxides (compounds contains the O2
2- group), where each oxygen is assigned an OS of -1.
H2O204/19/23 46
5. In binary compounds the element with the greater attraction for the electrons in the bond is assigned a negative OS equal to its charge in its ionic compounds.
HF, NH3, H2S, HI
6. The sum of the oxidation states must be zero for an electrically neutral compound and must be equal to the overall charge for an ionic species.
NH4+, CO3
2-
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Which Atoms Undergo Redox?
2H2 (g) + O2 (g) → 2H2O (g)
Zn (s) + Cu2+(aq) → Zn2+ (aq) + Cu(s)
2AgCl (s) + H2 (g) → 2H+ (aq) + 2Ag(s) + 2Cl- (aq)
2MnO4- (aq) + 16H+ (aq) + 5C2O4
2- (aq) → 2Mn2+(aq) + 10 CO2 (g) + 8 H2O (l)
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Methods for Balancing Redox Reactions
1. Oxidation states methodCdS + I2 + HCl → CdCl2 + HI + S
(1, 1, 2, 1, 2, 1)Cl2 + Ca(OH)2 → CaCl2 + Ca(ClO3) + H2O
( 6, 6, 5, 1, 6)
2. Half reaction method
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Balancing a Redox Equation by the Oxidation States Method
1. Assign the oxidation states of all atoms.2. Decide which element is oxidized and determine the
increase in oxidation state.3. Decide which element is reduced and determine the
decrease in oxidation state.4. Choose coefficients for the species containing the atom
oxidized and the atom reduced such that the total increase in oxidation state equals the total decrease in oxidation state.
5. Balance the remainder of the equation by inspection.
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The Half-Reaction or Ion-electron Method for Balancing Redox Reactions in Acidic Solutions
1. Split Rx into Half Reactions 2 parts of a REDOX RX- pick 1 to start then repeat oxidation - RA
reduction – OA2.Balance # of atoms first– not O or H3.Balance O by + H2O to side deficient in O
4.+ H+ to balance H5.Mass balance achieved
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6. Balance charges with e-7. Be sure # e- lost = #e- gained8. Cancel common terms on opposite side of →9. Σ the half Rx10. Check to make sure the Rx balances
Balance the equation in acid solution using the half reaction method
Cu(s) + HNO3 (aq) --> Cu2+ (aq) + NO(g)
The Half-Reaction or Ion-electron Method for Balancing Redox Reactions in Basic Solutions
1. Follow the same procedure as in acidic solutions2. +OH- to both sides to cancel out the H+
3. Make H2O from the OH- and H+
4. Cancel out H2O that is common to both sides
5. Be sure #e-lost = #e- gained6. Cancel common terms on opposite side of →7. Σ the half Rx8. Check to make sure the Rx balances
Balancing by Half Reaction Method
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Balance in acidic environment:
Cr2O72- (aq) + NO (g) → Cr +3 (aq) + NO3
- (aq)
Balance in basic environment:
Cr2O72- (aq) + NO (g) → Cr +3 (aq) + NO3
- (aq)
Cr2O72-(aq) + 2NO (g) + 6H+ (aq) → 2Cr3+ (aq) + 2NO3- (aq) + 3H2O (l)
Cr2O72-(aq) + 2NO (g) + 3 H2O --> 2Cr3+ (aq) + 2NO3- (aq) + 6OH- (aq)
Predicting Types of Redox RxSimple Redox
Hydrogen displacement Metal displacementHalogen displacement Combustion
DecompositionOxoanions
Table of Common Oxidizing and Reducing Agents
Atypical Redox Rx
1. Hydrogen + MO (hot) → M + HOH
2. MS + O2 → MO + SO2
3. Cl2 (g) + NaOH(dilute) → NaClO + NaCl + HOH
4. Cu + H2SO4 (conc) → CuSO4 + SO2 + HOH
5. Cu + HNO3 (dilute) → CuNO3 + NO + HOH
6. Cu + HNO3 (conc) → CuNO3 + NO2 + HOH
Disproportionation Reactions
Simultaneous oxidation and reduction of one species.
3NO2 + H2O → 2H+ + 2NO3- + NO
2H2O2(aq) → 2H2O(l) + O2(g)
Cl2(g) + 2OH-(aq) → ClO-(aq) + Cl-(aq) + H2O(l)
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