Ch 4 reactions in aqueous solutions
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CH 4 Reactions in Aqueous Solutions. Types of Equations Used to Describe Reactions in Solution. Molecular : overall reaction stoichiometry - not actual forms MgSO 4 ( aq ) + Na 2 CO 3 ( aq ) --> MgCO 3 (s) + Na 2 SO 4 ( aq )

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CH 4 Reactions in Aqueous Solutions

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Ch 4 reactions in aqueous solutions

CH 4 Reactions in Aqueous Solutions


Types of equations used to describe reactions in solution

Types of Equations Used to Describe Reactions in Solution

  • 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+ + CO32- --> MgCO3 (s) + 2Na+ + CO32-

    3. Net Ionic: includes only those solution components undergoing a change. Spectator ions not included.

    Mg2+ + CO32- --> MgCO3 (s)


Types of chemical reactions

Types of Chemical Reactions

Combination (Synthesis) reaction

A + B  AB

Decomposition reactionsAB  A + B

Displacement reactions

AB + C  AC + B

Metathetical (change of position) reactions (double-replacement reactions)

AB + CD  AD + CB

Combustion reactions reactions with oxygen

CxHy + nO2  xCO2 + (y/2) H2O


Combination reactions synthesis a b c

Combination Reactions (Synthesis): A + B → C

Metals + Oxygen:

  • Lithium + oxygen →

  • Magnesium + oxygen →

  • Gold + oxygen →

  • Platinum + oxygen →

    Remember the diatomics

    Metals 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 →


Combination reactions synthesis a b c1

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 →


Combination reactions synthesis a b c2

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)


Combination reactions synthesis a b c3

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 first

P4O10; CaO; H2O, CO2

Check Periodic Table


Decomposition reactions c a b

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?


Decomposition reactions special cases

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


Decomposition reactions special cases1

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)


Types of equations used to describe reactions in solution1

Types of Equations Used to Describe Reactions in Solution

  • 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+ + CO32- --> MgCO3 (s) + 2Na+ + CO32-

    3. Net Ionic: includes only those solution components undergoing a change. Spectator ions not included.

    Mg2+ + CO32- --> MgCO3 (s)


Writing equations

Writing Equations

Write a balanced molecular, ionic and net ionic equations for the following reactions:

  • Solution of silver nitrate was added to a solution of sodium chromate

  • A piece of solid zinc was placed in a solution of Copper(II) chloride

3.1


Single replacement or displacement reactions

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 metal

Active metal replaces H in water or acids

Nonmetal replaces less active nonmetal

Activity series – used to predict Rx

Standard Reduction Potential Chart and SHE


Single replacement reactions

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 solution

Molecular equation:

Net Ionic equation :

Redox?

2. zinc metal reacts with hydrochloric acid

3. aluminum metal reacts with sulfuric acid


Single replacement reactions1

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.html


Single replacement reactions halogen displacement

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


Double replacement reactions or metathetical reactions

Double Replacement Reactions orMetathetical Reactions

A+B- + C+D- A+D- + C+B-

Reactions occur to completion when:

Precipitate is produced

Gas is produced

Molecular substance such as H2O, CO2, NH3, SO2 are produced

Redox or NonRedox ?


Double replacement reactions or metathetical reactions1

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


Double replacement reactions or metathetical reactions2

Double Replacement Reactions orMetathetical Reactions

  • 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 formation

Double Replacement: Gas Formation

Common 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 acid

2. Ammonium chloride reacts with sodium hydroxide

3. Magnesium nitride reacts with water

4. Calcium sulfite reacts with hydrobromic acid

5. Sodium chloride + sulfuric acid

6. Sodium sulfide reacts with hydrochloric acid


Selective precipitation

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?


Combustion

Combustion

Write the products and balance the following combustion reaction:

C6H12O6 (s) + O2 →

C3H8O3 + O2 →

CH3OH + O2


Acids and bases arrhenius

Acids and Bases: Arrhenius

Acid

  • Any substance that releases H+ ion in aqueous solution

    Base

  • Any substance that releases OH- ion in aqueous solution


Br nsted lowery acid base definitions

Brønsted-Lowery Acid-Base Definitions

Anacid is a substance that donates a proton (H+) to a base

A baseis a substance that accepts a proton (H+) from an acid

conjugate base

conjugate. acid


Br nsted lowery acid base definitions1

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

Conjugate acid: ____________

Conjugate base: _________________


Compounds that act as br nsted acid and base

Compounds that act as Brönsted Acid and Base

Write equations for the following reactions. Identify the acid, base, conjugated acid and conjugated base:

  • HSO4-(aq) + H2O(l) →

  • HSO4-(aq) + H2O(l) →

  • H2O(l) + H2O(l) →

  • HCO3-1 (aq) + H2O(l)


Important acids and bases

Important Acids and Bases

Strong Acids:

HClhydrochloric

HBrhydrobromic

HIhydroiodic

HNO3nitric

H2SO4sulfuric

HClO4perchloric

Weak Acid:

CH3CO2Hacetic

Strong Bases:

NaOHsodium hydroxide

KOH potassium hydroxide

Ca(OH)2calcium hydroxide

Weak Base:

NH3ammonia


Ch 4 reactions in aqueous solutions

Ca(OH)2, Ba(OH)2 and Sr(OH)2

Group IIA, heavy metals)

Know the strong acids & bases!

3.2


Ch 4 reactions in aqueous solutions

STRONG acids in water:

100% of acid molecules form ions:

HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)

H3O+ is

hydronium ion


Ch 4 reactions in aqueous solutions

WEAK acids in water:

~5% or less of acid molecules form ions

(acetic, H3PO4, H2CO3)


Polyprotic acids multiple acidic h atoms

Polyprotic Acids: multiple acidic H atoms

H2SO4 H+ + HSO4-

HSO4-  H+ + SO42-

Not all H’s are acidic:

CH3CO2H


If h 3 po 4 reacts as an acid which of the following can it not make

If H3PO4 reacts as an acid, which of the following can it not make?

1. H4PO4+

2. H2PO4-

3. HPO42-

4. PO43-


Reactions involving weak bases

Reactions Involving Weak Bases

HCl(aq) + NH3(aq)  NH4+(aq) + Cl-(aq)

Net-Ionic Equation:

NH3(aq) + H+(aq)  NH4+(aq)

Spectator Ion?


Acid base reactions neutralization

Acid-Base Reactions: Neutralization

The “driving force” is the formation of water.

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(liq)

Net ionic equation

OH-(aq) + H+(aq) → H2O(liq)

“Spectator Ions”? __________________________

This applies to ALL reactions of STRONG acids and bases.


Acid base neutralization rx

Acid-Base Neutralization Rx

Polyprotic acids

H2SO4 (SA)or H3PO4 (WA)

H2SO4 : First H+ is ionized completely

H2SO4 → H+ + HSO4-

  • If base is excess: all H+ form H2O

  • If equimolar acid + base: only 1 H+ ionizes

  • Acidic anhydrides (NMO) + Basic anhydrides (MO) : react with H2O before acid or base


Ch 3 co 2 h aq naoh aq

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)


Hcn aq nh 3 aq

HCN(aq) + NH3(aq) 

Answer?

1. NH4+(aq) + CN-(aq)

2. H2CN+(aq) + NH2-(aq)

3. C2N2(s) + 3 H2(g)


Hydrolysis rx reverse neutralization

Hydrolysis Rx- Reverse Neutralization

Salt + H2O → molecular species

Formation of a weak acid and/or weak base

NH4+ + 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


Ch 4 reactions in aqueous solutions

  • 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

Oxidation-Reduction Reactions

Redox reactions:

involve a transfer of electrons.

Assigning oxidation states to an element in a molecule:

K2CrO4 LiSCN


Leo ger leo the lion says ger oil rig

LEO GER: Leo the Lion Says GEROIL RIG

Loss of Electrons is Oxidation

Gain of Electrons is Reduction

Oxidation Involves Loss

Reduction Involves Gain


Determination of oxidation states

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:


N 2 h 4 n 2 o 4 n 2 h 2 o

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.


Fe 2 o 3 2al al 2 o 3 2fe

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).


Rules for assigning oxidation states os

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 = -1

3. 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 O22- group), where each oxygen is assigned an OS of -1.

H2O2


Ch 4 reactions in aqueous solutions

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+, CO32-


Which atoms undergo redox

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) + 5C2O42- (aq) → 2Mn2+(aq) + 10 CO2 (g) + 8 H2O (l)


Methods for balancing redox reactions

Methods for Balancing Redox Reactions

1. Oxidation states method

CdS + 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


Balancing a redox equation by the oxidation states method

Balancing a Redox Equation by the Oxidation States Method

  • Assign the oxidation states of all atoms.

  • Decide which element is oxidized and determine the increase in oxidation state.

  • Decide which element is reduced and determine the decrease in oxidation state.

  • 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.

  • Balance the remainder of the equation by inspection.


The half reaction or ion electron method for balancing redox reactions in acidic solutions

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 – OA

  • Balance # of atoms first– not O or H

  • Balance O by + H2O to side deficient in O

  • + H+ to balance H

  • Mass balance achieved


Ch 4 reactions in aqueous solutions

  • Balance charges with e-

    • Be sure # e- lost = #e- gained

    • Cancel common terms on opposite side of →

    • Σ the half Rx

    • 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

The Half-Reaction or Ion-electron Method for Balancing Redox Reactions in Basic Solutions

  • Follow the same procedure as in acidic solutions

  • +OH- to both sides to cancel out the H+

  • Make H2O from the OH- and H+

  • Cancel out H2O that is common to both sides

  • Be sure #e-lost = #e- gained

    6. Cancel common terms on opposite side of →

    • Σ the half Rx

    • Check to make sure the Rx balances


Balancing by half reaction method

Balancing by Half Reaction Method

Balance in acidic environment:

Cr2O72- (aq) + NO (g) → Cr +3 (aq) + NO3- (aq)

Cr2O72-(aq) + 2NO (g) + 6H+ (aq) → 2Cr3+ (aq) + 2NO3- (aq) + 3H2O (l)

Balance in basic environment:

Cr2O72- (aq) + NO (g) → Cr +3 (aq) + NO3- (aq)

Cr2O72-(aq) + 2NO (g) + 3 H2O --> 2Cr3+ (aq) + 2NO3- (aq) + 6OH- (aq)


Predicting types of redox rx

Predicting Types of Redox Rx

Simple Redox

Hydrogen displacementMetal displacement

Halogen displacementCombustion

Decomposition

Oxoanions

Table of Common Oxidizing and Reducing Agents


Atypical redox rx

Atypical Redox Rx

  • Hydrogen + MO (hot) → M + HOH

  • MS + O2 → MO + SO2

  • Cl2(g) + NaOH(dilute) → NaClO + NaCl + HOH

  • Cu + H2SO4(conc) → CuSO4 + SO2 + HOH

  • Cu + HNO3(dilute) → CuNO3 + NO + HOH

  • Cu + HNO3 (conc) → CuNO3 + NO2 + HOH


Disproportionation reactions

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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