Overview
This lecture explains the definitions and properties of acids, bases, and alkalis, describes how the pH scale works, and details the neutralization reaction.
Acids
- Acids are substances that produce hydrogen ions (H⁺) in aqueous (water) solutions.
- Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and nitric acid (HNO₃).
- In aqueous solution, hydrochloric acid produces H⁺ and Cl⁻ ions.
- Sulfuric acid in solution produces H⁺ and SO₄²⁻ ions.
- Nitric acid in solution produces H⁺ and NO₃⁻ ions.
Bases and Alkalis
- Bases are chemicals that neutralize acids to form a salt and water.
- Most bases are metal oxides or metal hydroxides (e.g., copper oxide, iron(III) hydroxide, sodium hydroxide).
- Bases that dissolve in water are called alkalis.
- Insoluble bases (e.g., copper oxide, iron(III) hydroxide) are not alkalis.
- Sodium hydroxide is both a base and an alkali because it is soluble in water.
- In aqueous solution, alkalis produce hydroxide ions (OH⁻).
- Sodium hydroxide in water forms Na⁺ and OH⁻ ions.
The pH Scale
- The pH scale measures how acidic or alkaline a solution is.
- Acids have a pH between 0 and 6.
- A pH of 7 is neutral.
- Alkalis have a pH between 8 and 14.
- pH can be measured using a pH probe (electronic) or universal indicator (color change).
- Universal indicator: red = very acidic, green = neutral, purple = very alkaline.
Neutralization Reaction
- Acids produce H⁺ ions; alkalis produce OH⁻ ions.
- When acids and alkalis react, H⁺ and OH⁻ combine to form water (H₂O).
- The general equation for neutralization is: H⁺ + OH⁻ → H₂O.
Key Terms & Definitions
- Acid — A substance that releases hydrogen ions (H⁺) in aqueous solution.
- Base — A substance that neutralizes acids, forming salt and water.
- Alkali — A base that is soluble in water and produces hydroxide ions (OH⁻).
- Aqueous (aq) — Dissolved in water.
- Neutralization — Reaction of an acid with a base/alkali to form water and a salt.
- pH scale — A scale (0–14) that indicates acidity or alkalinity of a solution.
Action Items / Next Steps
- Learn and memorize the neutralization equation: H⁺ + OH⁻ → H₂O.
- Study the pH scale values and meanings.
- Review examples of acids, bases, and alkalis.