Assign.# 13.4

Acids/ Bases

Neutralization ReactionsRecall, one of the most common types of

reactions are acid/base reactions or neutralization reactions

We have various definitions of acids and bases, but they all react with characteristic properties.

NOTE – We will review some of the material from last year, but it is expected that you study all material previously taught.

Arrhenius Acid/BaseArrhenius’ theory of

acids/bases focuses on what molecules contain

An Arrhenius acid contains a H+

An Arrhenius base contains an OH-

Bronsted – Lowry Acid/BaseWhen Arrhenius’ definition

covers many acids/bases, acid/base reactions are not about containing H+ or OH-

A Bronsted-Lowry acid is any compound that gives H+ during the reaction

A Bronsted-Lowry base is any compound that accepts H+ during the reaction.

We will use this definition most of the time in this class

Lewis Acid/BaseUltimately, acid/base

reactions are not about H+, but about the accepting or donating of electron pairs.

A Lewis acid is an electron pair acceptor

A Lewis base is an electron pair donor

Every acid/base in the previous two categories are also acids/bases in this category

Broadest definition

Class ExampleIdentify the acid/base as Arrhenius, Bronsted –

Lowry, and/or Lewis:

Table TalkIdentify the acid/base as Arrhenius, Bronsted –

Lowry, and/or Lewis:

Strong vs. Weak Acid/Base• Acids/Bases can be classified as strong or

weak based on how much it disassociates.• Disassociate – To break apart• Acids/Bases that completely dissociate are

called strong acids/bases• Acids/Bases that only partially dissociate are

called weak acids/bases. These are in equilibrium with one another

Dissociation

Strong Acids/Strong Bases to Memorize

1. LiOH2. NaOH3. KOH4. RbOH5. CsOH6. Ca(OH)2

7. Sr(OH)2

8. Ba(OH)2

1. HBr2. HCl3. HI4. HNO3

5. H2SO4

6. HClO3

7. HClO4

Strong Bases

Strong Acids

The concentrations of acids and bases are often very low.

We use the pH scale to convey the concentration of H+

The pH scale is 0-14. Acid = pH 0-7Base = pH 7-14Neutral chemicals = pH

of 7.

I. pH

pH/pOHWe calculate the pH by:

pH=-log([H+])We calculate pOH by:

pOH=-log([OH-]) For strong acids and bases,

the concentration of the compound is the [H+] or [OH-]

For bases, we only know [OH-], so we need to first calculate pOH and then convert to pH using the equation:

pH = 14 – pOH

Class ExampleWhat is the pH of a 0.231 M solution of NaOH?

Table TalkWhat is the pH of a 0.512 M solution of HNO3?

Conjugate Acid/Base PairsAs with any reaction, there is a forward and

reverse reaction for acid/base reactions.Consider the following example:

HX + H2O H3O+ + X-

In the forward reaction HX is the acid because it donates H+ and H2O is the base because it accepts H+.

In the reverse reaction, H3O+ is now the acid and X- is now the base.

The pair of HX and X- are known as an conjugate acid-base pair

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Conjugate Acid/Base PairsEvery acid has a conjugate base that is

formed when a proton (H+) is removedEvery base has a conjugate acid that forms

when a proton is added

Class ExampleIdentify the acid, base, conjugate acid, and

conjugate base in the following reaction. Identify the acid/base as Arrhenius, Bronsted – Lowry, and/or Lewis:

NH3 + H2O NH4+ + OH-

Table TalkIdentify the acid, base, conjugate acid, and

conjugate base in the following reaction. Identify the acid/base as Arrhenius, Bronsted – Lowry, and/or Lewis:

HSO3- + H2O SO32- + H3O+