Acids & Bases
Chemistry · अम्ल और क्षार
📋Quick Overview
Acids are substances that release H⁺ ions in water (taste sour, turn blue litmus red). Bases release OH⁻ ions (taste bitter, feel soapy, turn red litmus blue). The pH scale (0-14) measures how acidic or basic a solution is. pH 7 = neutral, pH < 7 = acidic, pH > 7 = basic. The concept of pH was introduced by Sorensen in 1909.
📖Definitions of Acids & Bases
| Theory | Acid | Base | Example |
|---|---|---|---|
| Arrhenius | Gives H⁺ ions in water | Gives OH⁻ ions in water | HCl→H⁺+Cl⁻; NaOH→Na⁺+OH⁻ |
| Bronsted-Lowry | Proton (H⁺) donor | Proton (H⁺) acceptor | HCl donates H⁺; NH₃ accepts H⁺ |
| Lewis | Electron pair acceptor | Electron pair donor | BF₃ (acid); NH₃ (base) |
📖pH Scale & Indicators
- •pH scale ranges from 0 to 14. pH = -log[H⁺]
- •pH 0-6.9 = Acidic (more H⁺ ions). pH 7 = Neutral. pH 7.1-14 = Basic/Alkaline (more OH⁻ ions)
- •Lower pH = stronger acid. Higher pH = stronger base
| Indicator | In Acid | In Base | Neutral |
|---|---|---|---|
| Blue Litmus | Turns RED | No change (stays blue) | No change |
| Red Litmus | No change (stays red) | Turns BLUE | No change |
| Phenolphthalein | Colourless | Pink/Magenta | Colourless |
| Methyl Orange | Red/Pink | Yellow | Orange |
| Turmeric (Haldi) | Yellow (no change) | Red/Brown | Yellow |
📖Common Acids & Bases — Table
| Name | Formula | Type | Found In / Use |
|---|---|---|---|
| Hydrochloric acid | HCl | Strong acid | Stomach acid, cleaning |
| Sulphuric acid | H₂SO₄ | Strong acid | King of chemicals, batteries |
| Nitric acid | HNO₃ | Strong acid | Fertilizers, explosives |
| Acetic acid | CH₃COOH | Weak acid | Vinegar (5-8% solution) |
| Citric acid | C₆H₈O₇ | Weak acid | Lemon, orange (citrus fruits) |
| Carbonic acid | H₂CO₃ | Weak acid | Soda water, soft drinks |
| Sodium hydroxide | NaOH | Strong base | Caustic soda, soap making |
| Potassium hydroxide | KOH | Strong base | Caustic potash, soft soap |
| Calcium hydroxide | Ca(OH)₂ | Weak base | Slaked lime, whitewashing |
| Ammonium hydroxide | NH₄OH | Weak base | Cleaning agents |
📖pH of Common Substances
| Substance | pH (approx) | Nature |
|---|---|---|
| Battery acid | 0-1 | Strongly acidic |
| Stomach acid (HCl) | 1-2 | Strongly acidic |
| Lemon juice | 2-3 | Acidic |
| Vinegar | 2.5-3 | Acidic |
| Coffee | 5 | Weakly acidic |
| Milk | 6.5 | Slightly acidic |
| Pure water | 7 | Neutral |
| Blood | 7.35-7.45 | Slightly basic |
| Baking soda | 8.5 | Basic |
| Milk of magnesia | 10 | Basic |
| Bleach | 12-13 | Strongly basic |
| NaOH solution | 14 | Strongly basic |