Acids and Bases


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 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 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:

AcidPresent in
Acetic AcidVinegar
Ascorbic AcidAmla
Citric AcidCitrus Fruits
Formic AcidRed ants
Lactic AcidCurd
Tartaric AcidGrapes, Ripe Mangoes
Oxalic AcidTomato
Malic AcidApple
Hydrochloric AcidStomach
Butyric AcidButter
Stearic AcidFat
Amino AcidProtein
Tanic AcidTea

Some important bases:

Name of BaseFound in
(i) Calcium hydroxideLime water
(ii) Ammonium hydroxideWindow cleaner
(iii) Sodium hydroxideSoap
(iv) Potassium hydroxideSoap
(v) Magnesium hydroxideMilk of Magnesia

PH Scale:

  • 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:

SubstanceP H  Value
Vinegar2.4 -3.4
Human skin4.7
Blood7.3 to 7.5
Pure water7
Sea water8.5

Application of Acids:

Hydrochloric acidused for cleaning sinks and sanitry wares and in textile industry as a bleaching agent.
Nitric acidused in manufacture of fertilizers, paints, explosives
Tartaric acidused in making baking powder by mixing it with baking soda.
Citric acidmedicine
Acetic acidused in preservation of food and for enhancing flavor of food.
Sulphuric acidused in the batteries for cars, inverters

Application of Bases:

Calcium hydroxideused 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 hydroxidealso known as caustic soda is used manufacture of soaps, paper and textile.
Aluminium hydroxideused as foaming agent in fire extinguishers.
Ammonium hydroxideused in household cleaners and in fertilizers
Sodium carbonate+sulphuric acid used in fire extinguisher.