Acids and Bases

Chapter 10

Acid-Base Theories

• Properties of Acids and Bases

• Arrhenius Acid-Base Theory

• BrØnsted-Lowry Acid-Base Theory

• strong and weak acids and bases• acid nomenclature review

Properties of Acids and Bases

Acids• taste sour• conduct electricity in aqueous solution• turn litmus red• react with carbonates to produce

CO2(g)• react with active metals to produce

H2(g)

Examples of Acids

• citric acid• ascorbic acid• lactic acid• carbonic acid• muriatic acid (aka:

hydrochloric acid)

Bases

• feel slippery• taste bitter

• turn litmus blue• do not react with carbonates or with active

metals

Examples of Bases• drain cleaner and oven cleaner

(NaOH)• baking soda

(NaHCO3)

• washing soda

(Na2CO3)

• glass cleaner

(ammonia, NH3(aq))

• Na3PO4 (aka “TSP”)

Arrhenius Theory of Acids and Bases

Acids ionize in water to produce hydronium, H3O+(aq), ions.

eg. This is an ionization reaction.

HCl(g) + H2O(l) H3O+(aq) + Cl−(aq)

HCl(aq)

writes this equation as:

HCl(g) H+(aq) + Cl−(aq)

NB. The H+ ion does not exist as such in aq solution.

The hydronium ion is a hydrated proton, H+.

some fine print . . .

Some texts, like ours, abbreviate the hydronium ion, H3O+, as H+, called a hydrogen ion.

This is inaccurate!

H+ is a bare proton—which cannot exist in water. Take a look . . .

the aqueous hydronium ion:

What is the geometry of the hydronium ion?

pyramidal

Bases dissociate in water to produce one or more hydroxide, OH–(aq), ions.

eg. This is a dissociation reaction.

Na(OH)(s) Na+(aq) + OH–(aq)

Ba(OH)2(s) Ba2+(aq) + 2OH–(aq)

Limitations of the Arrhenius Theory

• restricted to acids & bases in aq solution• doesn’t explain behaviour of all acids or

bases• doesn’t explain certain types of

neutralization reactions

NH3(g) + HCl(g)

NH4Cl(s)

BrØnsted-Lowry Acid-Base TheoryAcid: proton (H+) donor

Base: proton (H+) acceptor

not restricted to aq. solutions

Explains

NH3(g) + HCl(g) NH4Cl(s)

(note that N in NH3 has a lone pair of e-s)

In order to qualify as a B-L acid, a compound must contain _____________.

(hydrogen)

In order to qualify as a B-L base, a

compound must contain ______________ .

(lone pair of e–s— or a negative charge)

Some B-L Acids & Bases

HCl(g) + H2O(l) H3O+(aq) + Cl−(aq)

B-L acid B-L base

NH3(aq) + H2O(l) NH4+(aq) + OH−(aq)

B-L base B-L acid

Water can act as either a B-L acid or base; water is amphiprotic.

Conjugate Acid-Base Pairs

HCl(g) + H2O(l) H3O+(aq) + Cl−(aq)

B-L acid B-L base conj acid conj base

NH3(aq) + H2O(l) NH4+(aq) + OH−(aq)

B-L base B-L acid conj acid conj base

How are conjugate acid-base pairs related?

By the transfer of a proton.

(Look again at previous slide.)

Identify conjugate acid-base pairs:

HCN(aq) + H2O(l) H3O+(aq) + CN−(aq)acid base c acid c base

H2PO4−(aq) + OH−(aq) HPO4

2−(aq) + H2O(l)acid base c base c acid

Strong Acids & Bases

A strong acid ionizes 100% in aq soln.eg.

HCl(aq) + H2O(l) H3O+(aq) + Cl−(aq)

HClO4(aq) + H2O(l) H3O+(aq) + ClO4−(aq)

100% rxn indicated by the “”

The “Big Seven” Strong AcidsHCl(aq) hydrochloric acid

HBr(aq) hydrobromic acid

HI(aq) hydriodic acid

HClO4(aq) perchloric acid

HClO3(aq) chloric acid

HNO3(aq) nitric acid

1 mol/L of these ↑ acids = 1 mol/L H3O+(aq)

H2SO4(aq) sulfuric acid

a diprotic acid1 mol/L acid>1 mol/L H3O+

Review of Acid Nomenclature on the next three slides—taken from nomenclature powerpoint

How does the name of each acid correlate to ending of anion name?

HCl(aq)Cl-, chloridehydrochloric acid

H2SO4(aq)SO4

2-, sulfatesulfuric acid

HNO2(aq)NO2

-, nitritenitrous acid

Ending of anion name of aciddetermines name of acid

1. anion ends in “-ide”hydro_____ic acid

[hydrobromic acid, HBr(aq), Br-, bromide]2. anion ends in “-ate”

_______ic acid[phosphoric acid, H3PO4(aq), PO4

3-, phosphate]

3. anion ends in “ite”_______ous acid

[nitrous acid, HNO2(aq), NO2-, nitrite ]

Examples of acidsformula name

HClO2(aq) _______________

chlorous acid

_______________ acetic (ethanoic) acid

HC2H3O2(aq)

H3PO3(aq) _______________

phosphorous acid

_______________ carbonic acid

H2CO3(aq)

Strong Bases

Strong Bases dissociate 100% in aq soln.

Include the soluble ionic hydroxides of alkali metals alkali earth metals

LiOH Sr(OH)2

NaOH Ba(OH)2

KOH Ca(OH)2 low solubility Mg(OH)2

These ionic hydroxides dissociate in water 100%:

NaOH(s)

Na+(aq) + OH−(aq)

Ba(OH)2

Ba2+(aq) + 2OH−(aq)

Concentrated vs Dilute Acids/Bases

Concentrated acids/bases:

lots of mol/L

eg H2SO4 5 mol/L

Dilute acids/bases:

few mol/L, say 0.1 mol/L

Describe each of the following acids as strong/weak and

dilute/conc1. 0.10 mol/L HNO3(aq)

a dilute, strong acid

2. 5% (m/v) CH3COOH(aq)

a dilute, weak acid

3. 10 mol/L H2SO4(aq)

a concentrated, strong acid

Weak Acids and Bases

Ionize less that 100%—usually much less—in aq solution. (eg acetic acid, CH3COOH)

+ H2O H3O+(aq) + CH3CO2

−

(aq)

represents < 100% yield (an equilibrium)

Example of weak base, ammonia:

NH3(aq) + H2O(l) NH4+(aq) + OH−(aq)

• ammonia ionizes only a few % • what does this say about the yield of this

rxn?

(only a few %)

Now indicate conj. acid-base pairs above.

NH3(aq) + H2O(l) NH4+(aq) + OH−(aq)

wk base acid c. acid c. base

Homework

10.1 LC # 1 – 12

RQ # 1 - 16