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UPPCS Chemistry Gap Sheet: Acids in Everyday Life and pH.
UPPCS has asked 19 of these. 1 have not been asked yet. Lock the first list, then read the second: it holds what UPPCS has not used yet.
First, the concept
Acids release hydrogen ions in water; bases accept them or provide hydroxide ions. A lower pH means a more acidic solution. At 25°C, neutral pure water has pH 7.
A fruit can contain several acids, so learn its characteristic acid without assuming it is the only one. Weak acid means incomplete ionisation, not low concentration. Neutralisation does not always produce a pH-7 salt solution.
✅ Already asked (19)
Food and natural sources
- Vinegar · Dilute aqueous acetic acid, CH₃COOH.
- Curd and sour milk · Lactic acid, C₃H₆O₃, forms during bacterial fermentation.
- Lemon and orange · Citric acid, C₆H₈O₇, is a characteristic acid.
- Grapes and tamarind · Tartaric acid, C₄H₆O₆, is a characteristic acid.
- Apple · Malic acid, C₄H₆O₅, is a characteristic acid.
- Ant secretion · Formic or methanoic acid, HCOOH, occurs in some ant secretions.
- Rancid butter · Butyric acid, C₄H₈O₂, contributes to its unpleasant smell.
- Vitamin C · Ascorbic acid, C₆H₈O₆; found in many fruits.
- Spinach · Contains oxalic acid, C₂H₂O₄, and oxalates.
- Soda water · Dissolved CO₂ forms some carbonic acid, H₂CO₃.
Mineral acids and mixtures
- Gastric juice · Contains hydrochloric acid, HCl.
- Lead-acid battery electrolyte · Dilute sulphuric acid, H₂SO₄.
- Nitric acid · HNO₃; a strong acid and common oxidising acid.
- Aqua regia · Fresh concentrated HCl and HNO₃ in a 3:1 volume ratio; dissolves gold.
- Boric acid · H₃BO₃; a weak acid used in some pharmaceutical preparations.
pH and indicators
- Fresh milk pH · Usually about 6.5–6.7; mildly acidic.
- Litmus test · Acid turns blue litmus red; base turns red litmus blue.
- Phenolphthalein · Colourless in acid; pink in a sufficiently alkaline solution.
- Antacid action · Mild bases neutralise excess stomach acid; strength and concentration are different.
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pH and indicators: 1
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⚠️ Sour milk contains lactic acid, not lactose as the acid; vinegar contains acetic acid.
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