Acids and Bases

Hydrogen fluoride

 Hydrochloric acid

Ammonium ion

Acetic acid

Sulphuric acid

Sodium hydroxide

Potassium hydroxide

 Acetate ion

Ammonia

Ammonium Hydroxide

Types of acids & bases

Arrhenius definition

acids are hydrogen-containing compounds that dissociate in water to give H+ ions or protons, while bases are hydroxide compounds that dissociate to give OH– ions

H+(aq)  + OH-(aq)  ⟶   H2O(l)

Li(aq) + F-(aq) ⟶   LiF(aq)

HF(aq) + LiOH(aq)  ⟶  H2O(l) + LiF(aq)

Arrhenius acid increases H+ conc

HF(aq)  ⇌  H+(aq) +  F-(aq)

LiOH(aq)  ⟶  Li+(aq)  +  OH-(aq)

Arrhenius base increases OH- conc

Neutralisation reaction

Examples:

Arrhenius acids

Arrhenius bases

Brønsted–Lowry definition

An acid is a species that donates a proton, while a base is one that accepts it

In this reaction, HCl donates a proton to NH3 and hence they act as Brønsted–Lowry acid and base respectively. According to Arrhenius theory, the above reaction would not be an acid-base reaction because neither species is forming H+ or OH- in water, but the chemistry involved is very similar to what would occur in aqueous phase

Brønsted–Lowry acids & bases

Brønsted–Lowry acids & bases

Lewis definition

A Lewis acid accepts an electron pair and Lewis base donates an electron pair.

The Lewis definition focuses on the movement of electrons rather than protons. AlCl3 and BCl3 are two examples of species that come under Lewis acids and none of the others, as they do not have protons to donate in a reaction.

BF3    +    NH3  ⟶  BF3NH3

Lewis acid

Lewis base

Acid-base adduct

Lewis acids & bases

Acids:

• Boron trihalides (ex BF3, BCl3)
• Organoboranes (ex B(OCH3)3 [trimethyl borate])
• RMgX (C6H5-Mg-Br, [phenylmagnesium bromide])
• AlX3 (ex AlCl3, AlH3, AlF3)

Bases:

• X- (ex F-, Br-, Cl-)
• PR3 (ex P(C6H5)3)
• Ethers (CH3–CH2–O–CH3 [methoxyethane])
• Thioethers ((CH3)2S [dimethylsulfide])
• Amines (C6H5NH2 [Aniline])
• Phosphine
• Compounds of O, S, Se and Te in oxidation state 2- (H2O)
• Simple & complex anions (H-, F-, SO2 4-)
• Lone-pair containing species (NH3, HO−, and CH3−)
• electron-rich π-system Lewis bases (ethyne, ethene, and benzene)

HSAB concept

HSAB concept - acids

HSAB concept - bases

pH scale

Measure of Hydrogen ion concentrations at logarithmic scale

Hydrogen ions concentrations in solutions are often very small, but can quickly change at an exponential rate hence a logarithmic scale is useful in quantifying these changes.

Similarly, hydroxide can be measured on a pOH scale:

Testing pH values

pH indicators are dyes that change colour at different concentrations of hydronium

Red litmus paper turns blue when exposed to a basic solution

Blue litmus paper turns red when exposed to an acidic solution

Ka, pKa, Kb, and pKb

Ka, pKa, Kb, and pKb are most helpful when predicting whether a species will donate or accept protons at a specific pH value.

Unlike pH, which depends on hydronium ion concentration, these are constant for a given acid or base

Ka = [H+][A-]/[HA]

pKa = - log Ka

Kb = [HA][OH-]/[A-]

pKb = -log Kb

Ka * Kb = Kw

Acid properties

Base properties

Acid vs Bases

1. Tastes sour

2. Turns blue litmus red

3. ph < 7

4. Can conduct electricity in solutions

5. React with active metals to produce H2

6. Arrhenius acids release H+ ions in solution

7. Brønsted–Lowry acids are H+ donors

8. Lewis acids are e- pair acceptors

1. Tastes bitter and feels slippery

2. Turns red litmus blue

3. ph > 7

4. Can conduct electricity in solutions

5.

6. Arrhenius bases release OH- ions in solution

7. Brønsted–Lowry bases are H+ acceptors

8. Lewis bases are e- pair donors

List of Inorganic Acids

List of Organic Acids

List of Bases