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Chapter: 8 Acids and BasesTitle: Lesson 1 Theories of Acids and BasesLearning Objectives:Reflect on prior knowledge of acids and bases

Understand the Bronsted-Lowry theory of acidity and identify Bronsted-Lowry acids and bases

1Solubility of Acids and AlkalisMost acids are soluble or react strongly with water

Some bases are soluble, some are insoluble

Soluble bases are called ALKALISAll About That Base (No Acid) :)

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I hereby define acids as compounds of oxygen and a nonmetal. (1777)In fact, I just named the newly discovered gas oxygen, which means acid-former.Antoine-Laurent de Lavoisier (1777)

Actually, one of the acids you worked with is composed entirely of hydrogen and chlorine (HCl). Humphry Davy (1818)

Antoine-Laurent de Lavoisier (1777)Awwwe SNAP! My definition wont work since it is no longer valid for all acids. I guess Ill go back to just being a tax collector.

The Arrhenius Theory of Acids and Bases: acids donate H+ in soln; bases donate OH-

Commentary on Arrhenius TheoryOne problem with the Arrhenius theory is that its not comprehensive enough. Some compounds act like acids and bases that dont fit the standard definition. Bronsted-Lowry Acids and BasesIts all about protons (H+)

Acid: Proton donorHCl(aq) H+(aq) + Cl-(aq)H2SO4(aq) 2H+(aq) + SO42-(aq)

Base: Proton acceptorNH3(aq) + H2O(l) NH4+(aq) + OH-(aq)OH-(aq)* + H+(aq) H2O(l)

*From any soluble hydroxide or other alkali

If we mention acid/base without mentioning the type, we generally mean a Bronsted-Lowry one.

Main MenuConjugate Acids and BasesA conjugate acid/base pair are two species that differ by a single proton.A conjugate base is a species that has one less protonA conjugate acid is a species that has one more proton

For example:Hydrochloric acid, HClHCl is the acid, Cl- is its conjugate baseThe HCl can donate a protonit is an acidThe Cl- could accept a proton.it is a base

Ammonia, NH3NH3 is the base, NH4+ is its conjugate acidThe NH3 can accept a proton.it is a baseThe NH4+ could donate a proton.it is an acid

What is the link?Main MenuConjugate PairsAcids react to form bases and vice versa. The acid-base pairs related to each other in this way are called conjugate acid-base pairs.They differ by just one proton.

HA + B A- + BH+acidconj. acidbaseconj. baseEx) List the conjugate acid-base pairs in the following reaction: CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)acidconj. acidbaseconj. baseconjugate pairconjugate pair

Amphoteric / amphiprotic substancesSubstances which can act as Bronsted-Lowry acids and bases, meaning they can either accept or donate a proton (capable of both).

The following features enable them to have this double-identity:

To act as a Bronsted-Lowry acid, they must be able to dissociate and release H+.To act as a Bronsted-Lowry base, they must be able to accept H+, which means they must have a lone pair of electrons.

Water is a prime example it can donate H+ and it has two lone pairs of electrons.Auto-ionization of water: H2O + H2O H3O+ + OH-

Water reacting as a base with CH3COOH:CH3COOH(aq) + H2O(l) CH3COO- (aq) + H3O+(aq) Water reacting as an acid with NH3: NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

Amphoteric / amphiprotic substancesWe think of water as a neutral substance but according to Bronsted-Lowry theory it can behave as an acid or as a base...A note on H+ and H3O+

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Solutions

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Main MenuKey PointsBronsted-Lowry TheoryAcid is a proton donorBase is a proton acceptor

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