Acids, Bases, Salts and Metals vs Non-metals

Acids and bases

• Acids taste sour, turn blue litmus red, pH < 7. Examples: HCl (stomach), citric acid (lemon), acetic acid (vinegar), lactic acid (curd), formic acid (ant sting).
• Bases taste bitter, feel soapy, turn red litmus blue, pH > 7. Examples: NaOH, milk of magnesia (antacid).
• pH 7 = neutral (pure water). Human blood pH ≈ 7.4.

Salts

Acid + Base → Salt + Water (neutralisation). Common salts: NaCl (table salt), baking soda NaHCO₃, washing soda Na₂CO₃·10H₂O, bleaching powder CaOCl₂, plaster of Paris CaSO₄·½H₂O.

Metals vs non-metals

Metals are lustrous, malleable, ductile and good conductors. Mercury is the only liquid metal; bromine is a liquid non-metal. Graphite is a non-metal that conducts electricity. Most reactive common metal: potassium; silver is the best conductor.

Exam tips

1. Ant sting → formic acid; treat with baking soda.
2. Rusting needs both oxygen and moisture; galvanisation uses zinc.

Analogy

The pH scale is like a see-saw with water sitting in the middle. Pile on acids and the see-saw tips toward the low numbers; add bases and it tips toward the high numbers. Neutralisation is putting equal weights on both ends so it balances again at 7.