Overview
This lecture covers the key concepts of acids, bases, and salts, including their physical and chemical properties, classification, pH scale, indicators, and methods for preparing salts.
Physical Properties of Acids and Bases
- Acids can be solids (like citric, oxalic, tartaric acids) or liquids (like sulfuric, acetic acids) at room temperature.
- Volatile acids evaporate easily; concentrated sulfuric acid is non-volatile.
- Most acids taste sour but some can taste bitter or sweet.
- Mineral acids are usually corrosive and can cause burns.
- Bases usually taste bitter and feel slippery (soapy) to touch.
- Some bases (sodium hydroxide, potassium hydroxide) are corrosive and damage skin.
Identification and Indicators
- Tasting or touching to identify acids/bases is unsafe and unreliable.
- Indicators are chemicals that show a color change in acidic or basic environments.
- Natural indicators: litmus (purple→red in acid, blue in base), turmeric, hydrangea flowers.
- Synthetic indicators: phenolphthalein (colorless in acid, pink in base), methyl orange (red in acid, yellow in base).
- Olfactory indicators (onion, vanilla, clove oil) are used for visually impaired—change or lose smell in acids/bases.
Classification of Acids and Bases
- By Source: Organic acids (from living things, contain C-H bond), Mineral (inorganic) acids (from rocks/minerals).
- By Oxygen presence: Hydra acids (no O, e.g., HCl), Oxy acids (contain O, e.g., H2SO4).
- By Basicity: Monobasic (1 H+ per molecule, e.g., HCl), Dibasic (2 H+, e.g., H2SO4), Tribasic (3 H+, e.g., H3PO4).
- Bases are classified by number of OH– ions they produce (mono, di, tri-acidic).
Strength of Acids and Bases
- Strong acids/bases completely dissociate in water (e.g., HCl, NaOH).
- Weak acids/bases partially dissociate (e.g., acetic acid, NH4OH).
- All alkalis are bases, but not all bases are alkalis (only water-soluble bases are alkalis).
Chemical Properties & Reactions
- Metals react with dilute acids to produce salt and hydrogen gas (effervescence).
- Metal carbonates/bicarbonates + acids → salt + water + CO2.
- Metal sulfites/bisulfites + acids → salt + water + SO2; metal sulfides + acids → salt + H2S.
- Neutralization: Acid + base → salt + water (double displacement reaction).
pH and pH Scale
- pH measures hydrogen ion (H+) concentration; scale ranges from 0 (most acidic) to 14 (most basic), 7 is neutral.
- pH below 7 = acidic, above 7 = basic.
- Universal indicator and pH paper show color changes to indicate pH strength.
Nature and Types of Salts
- Salts are ionic compounds made of cations (from base) and anions (from acid); they are electrically neutral.
- Types of salts:
- Neutral salt: from strong acid + strong base (pH = 7, e.g., NaCl).
- Acidic salt: from strong acid + weak base (pH < 7, e.g., NH4Cl).
- Basic salt: from weak acid + strong base (pH > 7, e.g., Na2CO3).
Preparation of Salts
- Combination reaction: multiple reactants form one product (e.g., iron + sulfur → iron sulfide).
- Displacement reaction: a more reactive metal displaces a less reactive one (zinc + HCl → zinc chloride + H2).
- Double displacement: precipitation (formation of insoluble salt), gas forming, or neutralization.
Key Terms & Definitions
- Acid — Substance producing H+ ions in water.
- Base — Substance producing OH– ions in water.
- Alkali — Water-soluble base.
- Indicator — Chemical showing color change in acid/base.
- pH — Power of hydrogen; scale for acidity/basicity.
- Neutralization — Reaction of acid and base forming salt and water.
- Salt — Ionic compound from acid and base reaction.
Action Items / Next Steps
- Review all indicator color changes for acids and bases.
- Memorize strong acids/bases lists and types of salts.
- Practice writing chemical reactions for acid, base, and salt formation.
- Prepare for next lecture: Analytical Chemistry.