Acids, Bases & Salts
Acids, Bases और Salts
Acids, Bases & Salts
- Chemistry
- Acids, Bases & Salts
Understand the pH scale and litmus, name the acids in everyday foods, and know the uses of baking soda, washing soda and bleaching powder.
🎯 Learning Objective
Understand the pH scale and litmus, name the acids in everyday foods, and know the uses of baking soda, washing soda and bleaching powder.
💡 Concept
- Acids taste sour, turn blue litmus red, and release H⁺ ions in water (e.g. HCl, H₂SO₄, HNO₃)
- Bases (alkalis) taste bitter, feel soapy, turn red litmus blue, and release OH⁻ ions (e.g. NaOH, KOH)
- The pH scale runs 0–14: pH 7 is neutral (pure water), below 7 is acidic, above 7 is basic
- The lower the pH, the stronger the acid; litmus is a natural indicator obtained from lichen
- Acids in foods: Citric acid (lemon, orange), Acetic acid (vinegar), Lactic acid (curd)
- More food acids: Tartaric acid (tamarind), Oxalic acid (tomato), Formic acid (ant sting), Ascorbic acid = Vitamin C
- Baking soda = Sodium bicarbonate (NaHCO₃) — used in cooking, as an antacid and in fire extinguishers
- Washing soda = Sodium carbonate (Na₂CO₃·10H₂O) — used in cleaning and to remove hardness of water
- Bleaching powder = Calcium oxychloride (CaOCl₂) — used to disinfect drinking water and to bleach fabrics
- Neutralisation: acid + base → salt + water (e.g. HCl + NaOH → NaCl + H₂O)
🧮 Key Formulas
pH 7 = neutral; < 7 acidic; > 7 basic
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Acid + Base → Salt + Water (neutralisation)
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Baking soda NaHCO₃ · Washing soda Na₂CO₃ · Bleaching powder CaOCl₂
✏️ Easy Example
Q. The pH value of a neutral solution such as pure water is: (a) 0 (b) 7 (c) 14 (d) 1
- Neutral means neither acidic nor basic
- That is exactly the middle of the 0–14 scale → pH 7
Answer: (b) 7
🇮🇳 Real-Life Example
The 'ENO' or baking-soda your family takes for acidity is chemistry at work — sodium bicarbonate is a mild base that neutralises the excess hydrochloric acid in your stomach, giving instant relief.
📝 Exam-Level Example
Q. Which acid is present in curd (dahi)? (a) Citric acid (b) Acetic acid (c) Lactic acid (d) Tartaric acid
- Milk turns to curd through fermentation
- The acid formed is lactic acid
Answer: (c) Lactic acid
📝 Exam-Level Example
Q. Which turns red litmus paper blue? (a) An acid (b) A base (c) Pure water (d) Vinegar
- Acids turn blue litmus red; the reverse means a base
- A base turns red litmus blue
Answer: (b) A base
🪄 Memory Trick
Litmus: 'Acid Attacks Blue' (blue→red in acid). Bases do the opposite (red→blue). For pH: lower = sourer/stronger acid. Vinegar = Acetic, Curd = Lactic, Lemon = Citric.
⚠️ Common Mistakes
- ❌ Thinking a higher pH means a stronger acid — it's the opposite (lower pH = stronger acid)
- ❌ Mixing up baking soda (NaHCO₃) and washing soda (Na₂CO₃)
- ❌ Saying acid turns red litmus blue — acids turn BLUE litmus RED
🏆 Exam Tips
- ✅ Map each food to its acid: lemon→citric, curd→lactic, vinegar→acetic, tamarind→tartaric
- ✅ Neutralisation always gives salt + water — a guaranteed one-mark idea
📌 Summary
- Acids: sour, blue→red litmus, release H⁺; Bases: bitter, red→blue litmus, release OH⁻
- pH 7 neutral, <7 acidic, >7 basic; lower pH = stronger acid
- Baking soda NaHCO₃, washing soda Na₂CO₃, bleaching powder CaOCl₂
- Acid + base → salt + water