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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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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:

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


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

Group IIA, heavy metals)

Know the strong acids & bases!

3.2


STRONG acids in water:

100% of acid molecules form ions:

HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)

H3O+ is

hydronium ion


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



Oxidation reduction reactions
Oxidation-Reduction Reactions in water.

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 GER in water.OIL 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 in water.

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
N in water.2 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
Fe in water.2O3 + 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) in water.

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


5 in water.. 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? in water.

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 in water.

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 in water.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 in water.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


  • Balance charges with e- in water.

    • 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 Reactions in

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 Reactions in

Simple Redox

Hydrogen displacement Metal displacement

Halogen displacement Combustion

Decomposition

Oxoanions

Table of Common Oxidizing and Reducing Agents


Atypical redox rx
Atypical Redox Rx Reactions in

  • 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 Reactions in

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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