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Acids definition

Acid and Defination of Acid 

If we cut a lemon with a knife and taste it, the lemon appears to have a sour taste .The sour taste of lemon is due to the presence of an acid in it . The acid present in lemon is due to  the presence of an acid in it . the acid present in the lemon which gives it a sour taste I citric acid . Thus : Acids are those chemical substance  which have a sour taste , acids change the color of blue litmus to red. Some of the common fruits such as a raw mango , raw grapes , lemon ,orange , and  tamarind (imli),etc., are in sour in taste due to the presence of acid in them . soured milk (or curd) also contain acid in it .The acids present in plant materials and animals are called organic acids. Organic acids are naturally occurring acids.

Some of the organic acids are :

Acetic acid (or Ethanoic acid), Citric acid, Lactic acid, Tartaric acid, Oxalic acid and Formic acid (or Methanoic acid).

Some of the natural sources of these organic acids are as follows : Acetic acid is found in vinegar (sir/ca), citric acid is present in citrus fruits such as lemons and oranges, lactic acid is present in sour milk (or curd), tartaric acid is present in tamarind and unripe grapes, oxalic acid is present in tomatoes whereas formic acid (or methanoic acid) is present in ant sting and nettle leaf sting. Organic acids (or naturally occurring acids) are weak acids. It is not harmful to eat or drink substances containing naturally occurring acids in them.
The acids prepared from the minerals of the earth are called mineral acids. Mineral acids are man-made acids. The three most common mineral acids are :
Hydrochloric acid, Sulphuric acid and Nitric acid. Concentrated mineral acids are very dangerous. They can burn our hands and clothes. These acids should be handled with care. In the laboratory, acids are  generally mixed with water to dilute them. Such acids are called dilute acids. Dilute acids are less harmful to us. Please note that carbonic acid is also a mineral acid. But it is a weak acid.

Strong Acids and Weak Acids

All the acids can be divided into two groups: strong acids, and weak acids.

  • Hydrochloric acid, sulphuric acid and nitric acid are strong acids.
  • Acetic acid (ethanoic acid), formic acid, citric acid, tartaric acid and carbonic acid are weak acids. acids. Only &iè mineral acid, :arbonic acid, is a weak acid. Strong acids are very dangerous to drink. Even the dilute 5olutions of strong acids are extremely harmful to drink. The organic acids are weak acids. The dilute solutions of weak acids are quite safe to drink. Being weak, the organic acids like acetic acid, citric acid and tartaric acid are used as food ingredients. For example, etic acid (in the form of vinegar) is used in making pickles; tartaric acid is used in king powder; whereas carbonic acid is used in fizzy soft drinks and soda water. The for some acids being strong and others being weak will be explained later on in :us chapter.

Concentrated and Dilute Acids

A concentrated acid is one which contains the minimum possible amount of water n it. The concentration of an acid is decreased by adding more water to it. When water
added to a concentrated acid, then a dilute acid is formed. Thus, a dilute acid is one which contains much more of water in it.

Dilute Acids

A dilute acid is obtained by mixing the concentrated acid with water. The process of mixing the concentrated acid with water is highly exothermic (or heat producing). So, when a concentrated acid and water are mixed together, a large aniount of heat is evolved. The dilution of a concentrated acid should always be done by adding concentrated acid to water gradually with stirring and not by adding water to concentrated acid. This is because:

  • when a concentrated acid is added to a water for  preparing a dilute acids then the heat is evolvedgradu0ally , and easily absorbed by the large amount of  water (to which acid is being adde d).
  • if, however water is added to concentrated acid to dilute  it , then a large amount of heat is evolved at once . this heat changes  some of the water to steam explosively which can splash the acids on our face or clothes  and cause acid burns . even the glass container break due to excessive heating .

The fact that the heat is evolved during the dilution of a concentration acid  can be shown as follow :

  • Take about 10ml of a water  in a breaker
  • add a few a drop of concentration sulphuric acid to water and  swirl the beaker slowly 
  • touch the bottom of the beaker 
  •  the bottom of the beaker to be hot showing the heat is evolved during the dilution of concentration sulphuric  acid . so , it is an exothermic process 

Properties of Acids 

The important properties of  acids are given below :

  • Acid have a sour taste 
  • Acid turns blue litmus to red 
  • Acid solutions conduct electricity (they are electrolyte ) When an acid is dissolved in eater , we get the acids solution . The solution of all the acids conduct Electricity. That is, acid solution allows electricity by acid solution will be explained later on).
  • acids react with metal to form hydrogen gas  When an acids react with a metal , then a salt  and hydrogen gas are formed

Check out Chemistry Formulas and NCERT Solutions for class 11 Chemistry prepared by Physics Wallah. 

 

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