An acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. A base is a molecule or ion able to accept a hydrogen ion from an acid.
Acid
Acids taste sour, can damage cells - citrus fruits, tomatoes and vinegar are acidic.Acids are corrosive in nature, good conductors of electricity and when reacted with metals, these substances produce hydrogen gas.
When we put a molecule of acid into water, it breaks apart and produces hydrogen(H+) ions. For example hydrochloric acid (HCl) dissociates into hydrogen ions (H+) and chloride anions (Cl-).
If we look at the formulas of different acids, we can see that they all contain at least one H (hydrogen):
HCl - hydrochloric acid
H2SO4 - sulfuric acid
HNO3 - nitric acid.
Organic Acids and their source
Organic acids are those which are obtained from the living organisms like plants and animals. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group ?COOH.| Acid | Source |
|---|---|
| Acetic acid (Ethanoic Acid) CH3COOH |
Vinegar |
| Formic Acid (Methonoic Acid) H2CO2 |
Ant sting, nettle sting |
| Citric Acid (C₆H₈O₇), Vitamin C (Ascorbic Acid-C6H8O6) |
Citrus fruits such as lemon, lime, orange, bananas etc. |
| Lactic Acid (C2H4OHCOOH) | Curd, Sour Milk |
| Oxalic Acid (H2C2O4) | Tomatoes, Rhubarb, spinach |
| Tarteric Acid (C4H6O6) | Grapes, tamarinds, pineapples, banana, unripe mangoes, Avocados |
| Maleic Acid (HO2CCH2CHOHCO2H) | Apples, Pears, Bananas and Grapes |
| Benzoic acid (C7H6O2) | Glass, Leaves, Urine |
| Tannic acid (C76H52O46) | Tea |
| Glutamic Acid (C5H9NO4) | Wheat |
| Uric Acid (C5H4N4O3) | Urine |
| Butyric Acid (CH3CH2CH2-COOH) | Rancid butter and milk |
| Ascorbic Acid (C6H8O6) | Tomato |
Base
Bases feel slippery to touch because they can change the structure of proteins.A strong base can cause severe chemical burns because it starts to damage the proteins in your skin.
Basic substances are used in many cleaning products.
A base is a substance that neutralises acids.
When bases are added to water, they split to form hydroxide ions (OH-), we call a base that has been added to water an alkaline solution.
If we look at some formulas for bases, we can see that they all contain hydroxide (OH-) ions:
NaOH - sodium hydroxide (caustic soda)
NH4OH - solution of ammonia in water
Ca(OH)2 - calcium hydroxide (builders' lime)
Common Alkali
| Common Alkali | |
|---|---|
| NaOH | Sodium hydroxide |
| KOH | Potassium hydroxide |
| Ca(OH)<sub>2</sub> | Calcium hydroxide |
| NH<sub>4</sub>OH | Ammonium hydroxide |
The turmeric is acidic in nature and it is yellow in color. When turmeric paste is added to the basic solution the yellow color changes to red color due to the neutralization reaction.
Potential of hydrogen (pH)
In order to find the numeric value of the level of acidity or basicity of a substance, the pH scale can be used.A pH scale measure can vary from 0 to 14, where 0 is the most acidic and 14 is the most basic a substance can be.
Another way to check if a substance is acidic or basic is to use litmus paper.
There are two types of litmus paper available that can be used to identify acids and bases - red litmus paper and blue litmus paper.
Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic (alkaline) conditions.
| ph | substance |
|---|---|
| 0 | Battery Acid |
| 1 | Stomach Acid |
| 2 | Vinegar |
| 3 | Orange Juice |
| 4 | Tomato |
| 5 | Black Coffee |
| 6 | Urine |
| 7 | Water |
| 8 | Sea Water |
| 9 | Baking Soda |
| 10 | Indigestion Tablets |
| 11 | Ammonia |
| 12 | Soapy Water |
| 13 | Bleach |
| 14 | Drain Cleaner |
Common things and their "pH" value
Any material with a pH value between 0 and 7 is known to be acidic while a pH value between 7 and 14 is a base.| Vinegar | 2 (Acidic) |
|---|---|
| Apples | 3 (Acidic) |
| Bananas | 4 (Acidic) |
| Tomato Juice | 4 (Acidic) |
| Black Coffee | 5 (Acidic) |
| Chocolate | 5 (Acidic) |
| Butter | 6 (Acidic) |
| Mango | 6 (Acidic) |
| Rice | 6 (Acidic) |
| Carrot | 6 (Acidic) |
| Milk | 6 (Acidic) |
| Honey | 4-6 (Acidic) |
| Potatoes | 5-6 (Acidic) |
| Shampoo | 5-7 (Acidic or neutral) |
| Water | 7 (Neutral) |
| Sugar | 7 (Neutral) |
| Eggs | 8 (Basic) |
| Borax | 9 (Basic) |
| Baking soda | 9 (Basic) |
| Lime water | 12 (Basic) |