Chapter: 8 Acids and Bases Title: Lesson 1 Theories of Acids and Bases Learning Objectives: – Reflect on prior knowledge of acids and bases – Understand the Bronsted-Lowry theory of acidity and identify Bronsted- Lowry acids and bases

Main Menu Solubility of Acids and Alkalis  Most acids are soluble or react strongly with water  Some bases are soluble, some are insoluble  Soluble bases are called ALKALIS All About That Base (No Acid) :)

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 My definition won’t work since it is no longer valid for all acids. I guess I’ll go back to just being a tax collector.

The Arrhenius Theory of Acids and Bases: acids donate H + in sol’n; bases donate OH - Commentary on Arrhenius Theory… One problem with the Arrhenius theory is that it’s not comprehensive enough. Some compounds act like acids and bases that don’t fit the standard definition.

Main Menu Bronsted-Lowry Acids and Bases  It’s all about protons (H + )  Acid: Proton donor  HCl(aq)  H + (aq) + Cl - (aq)  H 2 SO 4 (aq)  2H + (aq) + SO 4 2- (aq)  Base: Proton acceptor  NH 3 (aq) + H 2 O(l)  NH 4 + (aq) + OH - (aq)  OH - (aq)* + H + (aq)  H 2 O(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 Menu Conjugate Acids and Bases  A conjugate acid/base pair are two species that differ by a single proton.  A conjugate base is a species that has one less proton  A conjugate acid is a species that has one more proton  For example:  Hydrochloric acid, HCl  HCl is the acid, Cl - is its conjugate base  The HCl can donate a proton…it is an acid  The Cl - could accept a proton….it is a base  Ammonia, NH 3  NH 3 is the base, NH 4 + is its conjugate acid  The NH 3 can accept a proton….it is a base  The NH 4 + could donate a proton….it is an acid What is the link?

Conjugate Pairs Acids 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 + acid conj. acidbase conj. base

Ex) List the conjugate acid-base pairs in the following reaction: CH 3 COOH(aq) + H 2 O(l)  CH 3 COO - (aq) + H 3 O + (aq) acidconj. acidbaseconj. base conjugate pair

Main Menu Time to practice  Give the formula of the conjugate base for each of the following: 1. HF 2. H 2 SO 4 3. H 3 PO 4 4. CH 3 COOH 5. H 2 O 6. NH 4 +  Give the formula of the conjugate acid for each of the following: 1. OH - 2. SO HPO (CH 3 ) 2 NH 5. H 2 O

Amphoteric / amphiprotic substances Substances 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:” 1)To act as a Bronsted-Lowry acid, they must be able to dissociate and release H +. 2)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: H 2 O + H 2 O  H 3 O + + OH - Water reacting as a base with CH 3 COOH: CH 3 COOH(aq) + H 2 O(l)  CH 3 COO - (aq) + H 3 O + (aq) Water reacting as an acid with NH 3 : NH 3 (aq) + H 2 O(l)  NH 4 + (aq) + OH - (aq) Amphoteric / amphiprotic substances We 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 H 3 O + …

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Solutions

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Key Points  Bronsted-Lowry Theory  Acid is a proton donor  Base is a proton acceptor