Chapter 10: Acids, Bases and Salts

Learning Outcomes

• Define acid and acid anhydride.

• Investigate the reactions of non-oxidising acids with metals, carbonates, hydrogen carbonates, and bases.

• Define base and alkali.

• Investigate the reaction of bases with ammonium salts.

• Relate acidity and alkalinity to the pH scale.

• Discuss the strength of acids and alkalis based on their completeness of ionization.

• Define acidic, basic, amphoteric, and neutral oxides.

What are Acids?

• Fruits like apples and oranges taste sour due to acids.

• Indicators: Acids turn blue litmus paper red.

• Acids produce hydrogen ions (H) in water.

Definition of an Acid

• An acid is a substance that produces hydrogen ions, H⁺(aq), in water.

• Example: Hydrochloric acid dissociates in water:

  HCl(aq) ⟹ H⁺(aq) + Cl⁻(aq)

Chemical Properties of Acids

• Reaction with Metals:e.g.Mg + H2SO4 ⟹ MgSO4 + H2

• Reaction with Carbonates:e.g.CaCO3 + 2HCl ⟹ CaCl2 + H2O + CO2

• Reaction with Bases:

  e.g.H2SO4 + CuO ⟹ CuSO4 + H2O

  • This is called neutralization.

Strong vs. Weak Acids

Strong Acid

• A strong acid completely ionizes in water.

  • Examples: Sulphuric acid, Hydrochloric acid, Nitric acid.

Weak Acid

• A weak acid partially ionizes in water.

  • Examples: Ethanoic acid, Citric acid, Carbonic acid.

Common Acids and Their Uses

Properties of Bases and Alkalis

Definition

• Base: An oxide or hydroxide of a metal.

  • Examples: Sodium oxide, Copper(II) oxide.

• Alkali: A soluble base that produces hydroxide ions (OH⁻(aq)) in water.

  • Example: Sodium hydroxide (NaOH).

Properties

• Alkalis have a bitter taste and a soapy feel.

• They turn red litmus paper blue.

Chemical Properties of Alkalis

• React with acids to form salt and water:e.g.NaOH + HCl ⟹ NaCl + H2O

• React with ammonium salts to produce ammonia gas:e.g.NaOH + NH4Cl ⟹ NaCl + NH3 + H2O

Indicators

• Indicators show different colors in acidic and alkaline solutions.

  • Litmus: Red in acidic, blue in alkaline.

  • Methyl orange: Red below pH 4, yellow above.

  • Phenolphthalein: Colorless below pH 9, pink above.

pH Scale

• Measures acidity or alkalinity, ranging from 0 to 14.

  • Lower pH: More acidic

  • Higher pH: More alkaline

  • pH 7: Neutral (distilled water).

Types of Oxides

1. Acidic Oxides: Non-metal oxides that dissolve in water to form acids.

2. Basic Oxides: Metal oxides that dissolve in water to form alkalis.

3. Amphoteric Oxides: React with both acids and bases.

4. Neutral Oxides: Do not react with either acids or bases.

Salts

• Formed during the neutralization reaction between an acid and a base.

• Contains cation (from the base) and anion (from the acid).

Examples of Salts

Preparation of Salts

Methods

1. Action of acid on alkali: Titration.

2. Action of acid on insoluble base: e.g. CuO + H2SO4 ⟹ CuSO4 + H2O.

3. Action of acid on carbonate: e.g. H2SO4 + Na2CO3 ⟹ Na2SO4 + H2O + CO2.

4. Action of acid on a metal: e.g. H2SO4 + Zn ⟹ ZnSO4 + H2.

5. Double Displacement (Precipitation): Mixing solutions to produce an insoluble salt.

State Symbols in Reactions

• Solid → (s)

• Liquid → (l)

• Gas → (g)

• Aqueous solution → (aq)

Writing Ionic Equations

1. Break down the soluble reactants into ions.

2. Remove spectator ions.

3. Write the remaining ions that participate in the reaction.

Example of Ionic Equation

For the reaction of hydrochloric acid with sodium hydroxide:

1. HCl(aq) + NaOH(aq) ⟹ NaCl(aq) + H2O(l)

2. Ionic equation: H⁺(aq) + OH⁻(aq) ⟹ H2O(l)

Quick Checks

Include self-check questions on properties, definitions, and reaction mechanisms throughout the chapters to reinforce understanding.

Conclusion

Understanding acids, bases, and salts is crucial in chemistry. Mastery of the concepts enhances competency in practical applications and theoretical implications in chemistry.