Overview
This lecture explains acids and bases, the pH scale, methods for measuring pH, definitions and features of acids and bases, and common examples.
The pH Scale
- The pH scale measures acidity or alkalinity, ranging from 0 (most acidic) to 14 (most alkaline).
- A pH of 7 is neutral (neither acidic nor alkaline), as seen in pure water.
- Lower pH values indicate stronger acids; higher values indicate stronger alkalies.
Measuring pH
- Indicators are chemical dyes that change color at different pH levels, with universal indicator showing a range of colors from red (acidic) to purple (alkaline).
- pH probes with meters provide precise numerical pH measurements and reduce human error compared to color indicators.
Acids, Bases, and Alkalies
- Acids are substances forming solutions with pH below 7 by releasing hydrogen ions (H+) in water.
- Bases have pH above 7; those that dissolve in water are called alkalies.
- Alkalies produce hydroxide ions (OH–) in water.
Neutralization Reactions
- When acids react with bases, they form a salt and water in a neutralization reaction.
- Example: Hydrochloric acid + sodium hydroxide → sodium chloride (salt) + water.
- On the ionic level: H+ (acid) + OH– (base) → H2O (water).
- The resulting solution from neutralization typically has a pH of 7.
Common Acids and Bases
- Common acids: hydrochloric acid, sulfuric acid, nitric acid.
- Common bases: sodium hydroxide, calcium carbonate (hydroxides and carbonates).
Key Terms & Definitions
- pH scale — A numeric scale from 0 to 14 measuring acidity/alkalinity.
- Indicator — A dye that changes color depending on pH.
- pH probe — An electronic device for measuring pH.
- Acid — Substance with pH less than 7, releases H+ ions in water.
- Base — Substance with pH greater than 7.
- Alkali — A base that dissolves in water, forming OH– ions.
- Neutralization — Reaction between acid and base, creating salt and water.
- Salt — Product formed from acid-base neutralization.
Action Items / Next Steps
- Learn the names and properties of hydrochloric acid, sulfuric acid, nitric acid, sodium hydroxide, and calcium carbonate.
- Review the use of indicators and pH probes for measuring pH.
- Practice writing neutralization reactions and identifying products.