Chapter 7

Reactions in Aqueous Solutions

Chemistry B2A

Reactions in Aqueous Solutions

Ionic compounds

Aqueous solution: solvent is water

Reactions in Aqueous Solutions

In our body reactions occur in the aqueous solution.

Chemical reactions that occur in water.

Water in our body

1. About 60% of our body.

2. Most of the reactions occur in aqueous solution.

3. Participates in many biochemical reactions.

4. Transports reactants and products from one place in our body to another.

5. Eliminates the waste materials from cells and our body (urine).

Why does a chemical reaction occur?

1. Formation of a solid

2. Formation of water

3. Transfer of electrons

4. Formation of a gas

Several driving forces:

Why does a chemical reaction occur?

Several driving forces:

1. Formation of a solid

2. Formation of water

3. Transfer of electrons

4. Formation of a gas

Formation of a solid

Precipitation reactions

Precipitate

KI + Pb(NO3)2 ?

Ions Hydrated by H2OHydration

Ionic Compounds

When an ionic compound dissolves in water, ions are produced.

Ionic Compounds

1. Soluble solid: it completely dissolves in water (ions are formed).

2. Slightly soluble solid: it partially dissolves in water.

3. Insoluble solid: it does not dissociate in water (almost).

Ionic compounds = Salts

Ionic Compounds

Most chlorides (Cl-) and sulfates (SO42-) are soluble in water.

(except AgCl, PbCl2, BaSO4, CaSO4, PbSO4)

Most carbonates (CO32-), phosphates (PO4

3-), Sulfide (S2-), and hydroxides (OH-) are insoluble in water.

(except NaOH, KOH, Ba(OH)2, Ca(OH)2, and NH4OH)

All nitrates (NO3-) and acetate (CH3COO-) are soluble in water.

Most salts of Na+, K+, and NH4+ are soluble in water.

+ -electrolyte

Na+Cl-

bulb

Electrolytes

Electrolyte: conducts an electric current.

Ionization (Dissociation)

NaCl → Na+ + Cl-

strong electrolytes: molecules dissociate completely into ions (NaCl).

weak electrolytes: molecules dissociate partially into ions (CH3COOH).

nonelectrolytes: molecules do not dissociate into ions (DI water).

Formation of a solid

Precipitation reactions

Precipitate

KI + Pb(NO3)2 ?

Aqueous Solution (ionic compounds)

KI(s) K+(aq) + I-(aq) Dissociation(Ionization)

aqueous solution: solvent is water

H2OKI

Pb(NO3)2

K+

Pb(NO3)2(s) Pb2+(aq) + 2NO3-(aq)

H2O

I-

Pb2+

NO3-

NO3-

2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)

Aqueous Solution (ionic compounds)

KI Pb(NO3)2

K+

I- Pb2+

NO3-

2K+(aq) + Pb2+(aq) + 2I-(aq) + 2NO3-(aq) PbI2(s) + 2K+(aq) + 2NO3

-(aq)

CompleteIonic equation:

Molecular equation:

2As3+(aq) + 3s2-(aq) As2S3(s)

total charge on left side = total charge on right sidebalanced equation

2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)

2K+(aq) + Pb2+(aq) + 2I-(aq) + 2NO3-(aq) PbI2(s) + 2K+(aq) + 2NO3

-(aq)

Pb2+(aq) + 2I-(aq) PbI2(s)Net ionic equation:

Spectator ions

Why does a chemical reaction occur?

1. Formation of a solid

2. Formation of water

3. Transfer of electrons

4. Formation of a gas

Several driving forces:

Acids and Bases

Acids: sour

Bases: bitter or salty

Acids and Bases

NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

Acid: produces H3O+ (H+) in water.

Base: produces OH- in water.

Arrhenius definition:

CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)

H3O+ (Hydronium ion): H+(aq) + H2O(l) H3O+(aq)

NaOH(s) Na+(aq) + OH-(aq)H2O

Acids and Bases

Weak acid and base: it is partially ionized in aqueous solution.

CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)

Strong acid and base: it is completely ionized in aqueous solution.

HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq)

NaOH(aq) + H2O(l) Na+(aq) + OH-(aq)

NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

produces less H+ and OH-

produces more H+ and OH-

Acid-Base Reactions

Neutralization

A strong acid and a strong base react together to produce a salt and water.

NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) + Na+(aq) + Cl-(aq) + H2O(l)

H+(aq) + OH-(aq) H2O(l)

The only chemical change is the formation of water.

Why does a chemical reaction occur?

1. Formation of a solid

2. Formation of water

3. Transfer of electrons

4. Formation of a gas

Several driving forces:

Na → Na+ + e-

Cl + e- → Cl-

Oxidation and Reduction reactions (redox)

2Na(s) + Cl2(g) 2NaCl(s)

e-

Metal + Nonmetal : Transfer of electrons

Oxidation and Reduction reactions (redox)

Oxidation and Reduction reactions (redox)

Zn(s) Zn2+(aq) + 2e- Zn is oxidized (reducing agent)

Cu2+(aq) + 2e- Cu(s) Cu2+ is reduced (oxidizing agent)

oxidation: it is the loss of electrons.reduction: it is the gain of electrons.

Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) redox reaction

Oxidation and Reduction reactions (redox)

oxidation: is the gain of oxygen / loss of hydrogen.reduction: is the loss of oxygen / gain of hydrogen.

CH4(s) + 2O2(g) CO2(g) + 2H2O(g) redox reaction

C gains O and loses His oxidized

(reducing agent)

O gains HIs reduced

(oxidizing agent)

single replacement reaction and combustion reactions redox reactions

double replacement reactions non redox

Classification of chemical reactions

Chemical reactions

PrecipitationReactions

Oxidation-ReductionReactions

Acid-BaseReactions

CombustionsReactions

Synthesis (combination)Reactions

(Reactants are elements.)

Decomposition (Analysis)Reactions

(Products are elements.)