Explore the pH scale, how indicators reveal a substance's nature, and how acids and bases neutralize each other to form salts.
The pH scale runs from 0 to 14. Values below 7 are acidic, exactly 7 is neutral, and above 7 is basic (alkaline).
Lemon juice has pH ≈ 2. Is it acidic, neutral, or basic?
Acidic (pH well below 7)
Soap solution has pH ≈ 9–10. Is it acidic, neutral, or basic?
Basic (pH above 7)
Indicators change colour depending on whether a solution is acidic or basic — useful when you can't just "look" at pH directly.
Litmus paper turns red in a solution. Is the solution acidic or basic?
Acidic (blue litmus turns red in acid; red litmus stays red)
Phenolphthalein turns pink in a solution. Is the solution acidic or basic?
Basic (phenolphthalein is colourless in acid, pink in base)
When an acid reacts with a base, they neutralize each other, forming a salt and water.
Write the neutralization reaction between HCl and NaOH.
HCl + NaOH → NaCl + H₂O (balanced: 1 H, 1 Cl, 1 Na, 1 O on each side after accounting for H₂O)
Balance: Zn + HCl → ZnCl₂ + H₂ (a metal reacting with an acid)
Zn + 2HCl → ZnCl₂ + H₂
1. A solution has pH 5. Is it acidic, neutral, or basic?
2. A solution has pH 13. Is it acidic, neutral, or basic?
3. Blue litmus is dipped in vinegar. What colour does it turn?
4. What are the two products when an acid neutralizes a base?
5. Balance: Mg + HCl → MgCl₂ + H₂