Acids & Bases

Arrhenius acid

is a substance that dissociates in water to produce H⁺ ions

Examples of Arrhenius acid

HCL —→ H⁺ + CL^- = monobasic

H₂SO₄ —→ 2H⁺ +SO₄^2- = Dibasic

H₃PO₄ —→ 3H⁺ + PO₄^3- = Tribasic

What does Strong Arrhenius acids

dissociate fully in water

What does Weak Arrhenius acids

dissociate partially in water

Example of Strong Arrhenius acids

HCL

Example of Weak Arrhenius acids

Ethanoic

Arrhenius base

is a substance that dissociates in water to produce OH ions

Examples of Arrhenius base

NaOH —→ Na⁺ + OH^-

Mg(OH)₂ —→ Mg²⁺ + 2OH^-

Ca(OH)₂ —→ C²⁺ + 2OH

Strong Arrhenius base

dissociate fully in water

Weak Arrhenius base

dissociate partially in water

Example of Strong Arrhenius base

NaOH

Example of Weak Arrhenius base

Na₂CO3

Limitation to the Arrhenius Theory

1. Its hydronium ions in solution not hydrogens ions

2. Arrhenius restricted his definition to aqueous solution only

3. Arrhenius didn’t account for amphoteric substances such as water

Bronsted-Lowry acid

is a proton (H⁺) donor

Bronsted-Lowry Strong Bronsted-Lowry acids

are good proton donors

Example of Strong Bronsted-Lowry acid

• HCL

• H₂SO₄

• HNO3

Weak Bronsted-Lowry acids

are poor proton donors

Examples of Weak Bronsted-Lowry acid

CH₃COOH

Bronsted-Lowry base

is proton (H⁺) acceptor

Strong Bronsted-Lowry bases

are good protons acceptor

Example of Strong Bronsted-Lowry bases

NaOH

KOH

Ca(OH)₂

Weak Bronsted-Lowry base

are poor proton acceptors

Example of Weak Bronsted-Lowry base

NH3

Conjugate base

an acid changes into its conjugate base when it donates a proton

Conjugate acid

a base changes into its conjugate acid when it accepts a proton

Conjugate acid-base pair

is any pair of substance that differ by a proton

Salt

is the substance formed when the H⁺ from an acid is replace with a metal or ammonium

Neutralisation

is the reaction between an acid & base to form salt & water

Types of Neutralisation Reaction

1. Acid + Metal —→ Salt + Hydrogen

2. Acid + Base —→ Salt + Water

3. Acid + Carbonate —→ Salt + Water + Carbon Dioxide

Example of Acid + Metal —→ Salt + Hydrogen

2HCl + Zn —→ ZnCl₂ + H2

Example of Acid + Base —→ Salt + Water

HCl + NaOH —→ NaCl + H₂O

Example of Acid + Carbonate —→ Salt + Water + Carbon Dioxide

2HCl + Na₂CO₃ —→ 2NaCl + H₂O + CO2

Everyday Life Example of Neutralisation

1. Medicine - Excess HCl in the stomach cause heartburn. Antacids like Gaviscon contain sodium hydrogencarbonate to neutralise the acid

2. Agriculture - If soil is too acidic, lime (CaO, Calcium oxide) is added to neutralise the acidity. Lime & water make calcium hydroxide, a base. This is base reacts with the acid in the soil

3. Environmental Protection - Some areas receive high amounts of acids rains, making lakes very acidic. Limestone is added to these lakes to neutralise the acid