Acids, Bases and Salts — Practice

Question 1

What is the pH of a neutral solution?

Accepted Answer

✦ Answer: pH = 7 (e.g., pure water). pH < 7 acidic, pH > 7 basic.

Question 2

Write the neutralisation reaction of HCl and NaOH.

Accepted Answer

✦ Answer: HCl + NaOH → NaCl + H₂O. Acid + Base → Salt + Water.

Question 3

Identify the type of substance: (a) turns red litmus blue, (b) tastes sour, (c) has pH 9, (d) reacts with Mg to give H₂.

Accepted Answer

Step 1 — Red litmus → blue: BASE
Step 2 — Sour taste: ACID
Step 3 — pH 9 (> 7): BASE
Step 4 — Reacts with Mg → H₂: ACID (acid + metal → salt + hydrogen)

✦ Answer: (a) Base, (b) Acid, (c) Base, (d) Acid.

Question 4

Discuss the importance of pH in everyday life with at least 4 examples.

Accepted Answer

Step 1 — Stomach pH.
  Stomach has pH ~1-3 (strong HCl) for DIGESTION. Excess acid causes ACIDITY/HEARTBURN. Treatment: ANTACIDS (Mg(OH)₂ — milk of magnesia) neutralise excess acid.

Step 2 — Tooth decay.
  Tooth enamel made of CALCIUM PHOSPHATE. It DISSOLVES below pH 5.5. Bacteria in mouth convert sugar to acid, lowering pH. Result: cavities.
  PREVENTION: brush teeth (remove food), use toothpaste (basic), avoid excess sugar.

Step 3 — Soil pH.
  Plants grow best at pH 6-7. If soil too ACIDIC: add LIME (basic) like Ca(OH)₂. If too BASIC: add COMPOST (slightly acidic).
  Indian farmers test soil pH for crop selection.

Step 4 — Acid rain.
  Rain with pH < 5.6 due to SO₂, NO₂ pollution.
  DAMAGES: crops, lakes (fish die), buildings (eats marble — Taj Mahal at risk), forests.
  SOLUTIONS: reduce vehicle/factory emissions, use renewable energy.

Step 5 — Bee/wasp sting.
  BEE sting: ACIDIC (formic acid). Treatment: rub baking soda (mildly basic).
  WASP sting: BASIC. Treatment: vinegar (acidic).
  Knowledge of pH helps medical treatment.

Step 6 — Self-defense of plants/animals.
  NETTLE plant has acidic stings (formic acid).
  Rubbing DOCK plant leaves (basic) provides relief.

Step 7 — Indian context.
  Yamuna and Ganga have pH issues from pollution.
  Acid rain damages historical monuments (Taj Mahal Sutluj).
  pH balance critical for Indian agriculture and health.

✦ Answer: pH matters in: (1) STOMACH (HCl for digestion; antacids for excess); (2) TEETH (enamel dissolves below pH 5.5; sugar causes cavities); (3) SOIL (pH 6-7 for crops; add lime for acidic soil); (4) ACID RAIN (damages crops, buildings; control pollution); (5) STINGS (bee sting acidic, treat with baking soda; wasp sting basic, treat with vinegar). pH knowledge protects health, environment, agriculture.

Practice — Acids, Bases and Salts

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