Acids and Alkali

1⃣ Acids

Definition:

• Substances that have a sour taste

• Can burn or irritate skin

• Turn blue litmus paper red

Examples:

• Lemon juice 🍋

• Vinegar

• Fizzy drinks

Properties:

• pH less than 7

• Strong acids → red on universal indicator

• Weak acids → orange/yellow

• 2⃣ Alkalis

  Definition:

  • Substances that dissolve in water and have a bitter taste

  • Feel slippery/soapy

  • Turn red litmus paper blue

  Examples:

  • Soap 🧼

  • Toothpaste

  • Baking soda

  Properties:

  • pH greater than 7

  • Weak alkali → blue

  • Strong alkali → purple

3⃣ pH Scale

4⃣ Neutralisation

Definition:

• When an acid reacts with an alkali, they cancel each other out, producing:
  Acid + Alkali → Salt + Water

Key points:

• pH moves towards 7

• Universal indicator colour moves towards green

Examples:

• Lemon juice + soap → neutralisation

• Hydrochloric acid + sodium hydroxide → salt + water

Safety rules:

• Always wear goggles and gloves

• Never taste chemicals

5⃣ Gases Produced by Acids

1. Hydrogen (H₂)

• Produced when acids react with metals

• Observations: bubbles/fizzing

• Test: bring a lit splint → “pop” sound