Water
Vinegar
Lemon juice
Slaked lime
Substances with a sour taste are regarded as acids. Lemon juice, vinegar, grapefruit juice and spoilt milk, etc. taste sour since they are acidic. Many substances can be identified as acids based on their taste but some of the acids like Sulphuric acid have very strong action on the skin which means that they are corrosive in nature. In such cases, it would be according to the modern definition: An acid may be defined as a substance which releases one or more H+ ions in aqueous solution.
Substances with bitter taste and soapy touch are regarded as bases. Since many bases like sodium hydroxide and potassium hydroxide have corrosive action on the skin and can even harm the body, so according to the modern definition – A base may be defined as a substance capable of releasing one or more OH- ions in aqueous solution.
ALKALIES: Some bases like sodium hydroxide and potassium hydroxide are water soluble. These are known as alkalies. Therefore water soluble bases are known as alkalies eg. KOH, NaOH. A list of a few typical bases along with their chemical formulae and uses is given below-
| Name | Commercial Name | Chemical Formula | Uses |
| Sodium hydroxide | Caustic Soda | NaOH | In manufacture of soap, paper, pulp, rayon, refining of petroleum etc. |
| Potassium hydroxide | Caustic Sba | KHO | In alkaline storage batteries, manufacture of soap, absorbing CO2 gas etc. |
| Calcium hydroxide | Slaked lime | Ca(OH)2 | In manufacture of bleaching powder softening of hard water etc. |
| Magnesium hydroxide | Milk of Magnesia | Mg(OH)2 | As an antacid to remove acidity from stomach |
| Aluminum hydroxide | – | Al(OH)3 | As foaming agent in fire extinguishers. |
| Ammonium hydroxide | – | NH4OH | In removing grease stains from cloths and in cleaning window panes. |
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