Acids and Bases
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Acids and Bases are the main categories of chemical compounds. They have certain definite properties.
- The word ‘acid’ is derived from a Latin word, which means “sour”.
- Organic acids: These acids contain carbon as a constituent and are present in organic matter i.e, animals and plants. For example Citric acid, acetic acid, tartaric acid etc. Organic acids are weak acids.
- Mineral Acids: These acids are prepared from minerals present in the Earth’s crust. For example sulphuric acid, hydrochloric acid , nitric acid,etc. These are also called laboratory acids. Mineral acids are strong acids.
- Sulphuric acid is known as the king of chemicals.
- Bases are substances that, in aqueous solution, release hydroxide (OH−) ions, are slippery to the touch, can taste bitter eg: Milk of Magnesia,baking soda, washing soda, calcium hydroxide, etc.
Weak and Strong Bases:
Strong bases: Some bases are readily soluble in water. These are strong bases. These are also called alkalies.eg: sodium hydroxide and potassium hydroxide.
- Strong bases are very corrosive and can burn the skin
Weak bases: Some bases are insoluble or partly soluble in water such bases are called weak bases.eg: ammonium hydroxide, calcium hydroxide etc.
Arrhenius concept of acids and bases:
- Acid is a substance which produces hydrogen ions in aqueous solution e.g. HCL (H+ Cl–), Sulphuric Acid,H2SO4(2H+ SO2-4).
- Base is a substance which produces Hydroxide ion (OH–) in aqueous solution e.g. sodium hydroxide and ammonium hydroxide etc.
Lewis concept of Acids and Bases:
- An acid is a substance which can accept an electron e.g. boron fluoride (BF3) and carbon dioxide.
- Base is a substance which can produce an electron e.g. fluoride (F–) and chloride (Cl–).
Bronsted Lowery concept of Acids and Bases
- An acid is a molecule or ion which is capable of donating a proton.
- A base is a molecule or ion which is capable of accepting a proton.
Some important acids:
|Citric Acid||Citrus Fruits|
|Formic Acid||Red ants|
|Tartaric Acid||Grapes, Ripe Mangoes|
Some important bases:
|Name of Base||Found in|
|(i) Calcium hydroxide||Lime water|
|(ii) Ammonium hydroxide||Window cleaner|
|(iii) Sodium hydroxide||Soap|
|(iv) Potassium hydroxide||Soap|
|(v) Magnesium hydroxide||Milk of Magnesia|
- PH value is a measure of the acidity or basicity of an aqueous solution.
- Solution with PH value less than 7 is considered as acidic.
- Solution with PH value greater than 7 is considered as basic.
PH values of some important solutions:
|Substance||P H Value|
|Blood||7.3 to 7.5|
Application of Acids:
|Hydrochloric acid||used for cleaning sinks and sanitry wares and in textile industry as a bleaching agent.|
|Nitric acid||used in manufacture of fertilizers, paints, explosives|
|Tartaric acid||used in making baking powder by mixing it with baking soda.|
|Acetic acid||used in preservation of food and for enhancing flavor of food.|
|Sulphuric acid||used in the batteries for cars, inverters|
Application of Bases:
|Calcium hydroxide||used as an ingredient in whitewash, neutralizing acidic soil, in making bleaching powder and softening hard water.|
|Magnesium hydroxide||also known as milk of magnesia is used as an antacids.|
|Sodium hydroxide||also known as caustic soda is used manufacture of soaps, paper and textile.|
|Aluminium hydroxide||used as foaming agent in fire extinguishers.|
|Ammonium hydroxide||used in household cleaners and in fertilizers|
|Sodium carbonate+sulphuric acid||used in fire extinguisher.|