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Chemistry || Acids, Bases, Salts and PH Indicators



Properties of Acids, Bases, Salts and PH Indicators

ACID :

  • Acid is a substance which produces hydrogen ions (H+) in aqueous solution e.g. HCL (H+ Cl-).
  • An acid is a chemical substance that has a sour taste.
  • Many food items have (such as lemons, curd, vinegar and orange) taste sour because of the presence of acid in them.
  • Examples of strong acids are: hydrochloric acid, sulphuric acid, nitric acid etc.
  • Examples of Weak Acid are: Acetic acid, formic acid, carbonic acid etc.

Natural Acids: These are obtained from natural sources such as fruits and animal products. For e.g. lactic, citric, and tartaric acid etc.

Mineral Acids: Mineral acids are acids prepared from minerals. For example, Hydrochloric acid (HCL), Sulphuric acid (H2SO4), and Nitric acid (HNO3) etc.

Uses of Acids:

  • Hydrochloric acid (HCL) present in our stomach helps in the digestion of food.
  • Vitamin C or ascorbic acid gives the needed nutrients for body.
  • Carbonic acid is used in making carbonated beverages and fertilizers.
  • Vinegar a preservative, is a dilute form of Acetic acid.
  • Sulphuric acid is used in the manufacture of fertilizers, paints, synthetic fibers etc.
  • Nitric acid is used in the preparation of Aqua-Regia, used in the purification of precious metals like gold and silver.
  • Boric acid is used to wash eyes.
  • Phosphoric acid is used in making fertilizers and detergents.

 

Sources of the AcidName of the Acid
VinegarAcetic Acid
Citrus fruitsCitric Acid
Grapes, Tamarind, Gooseberries, Ripe Mangoes.Tartaric Acid
Sour milkLactic Acid
ApplesMalic Acid
CurdButyric Acid
Tea, Tomatoes, SpinachOxalic Acid
Red-Ants and BeesFormic Acid
ProteinsAmino Acids
Amla, Guava, orangesAscorbic Acid

BASE :

  • Base is a substance which produces Hydroxide ion (OH-) in aqueous solution e.g. sodium hydroxide and ammonium hydroxide etc.
  • Bases are bitter in taste and soapy to touch.
  • Bases are found in different substances such as bleach, ammonia, washing powder and soap.
  • Bases are also called Alkaline.
  • All alkalis are bases but all bases are not alkalis.

Note: – Neutral Substance is any substance which is neither acidic nor basic in nature.

SALT :

  • When acidic and basic solutions are mixed in proper proportion, they lose their own nature and a new product – Salt is formed.
  • Salts are the ionic compounds which are produced after the neutralization reaction between acid and base.
  • Salts are electrically neutral.
  • A salt may be acidic, basic or neutral in nature.
    • Neutral Salt: Salts produced because of reaction between a strong acid and strong base are neutral in nature. The pH value of such salts is equal to 7, i.e. neutral.
    • Acidic Salts: Salts which are formed after the reaction between a strong acid and weak base are called Acidic salts. The pH value of acidic salt is lower than 7.
    • Basic Salts: Salts which are formed after the reaction between a weak acid and strong base are called Basic Salts.
  • There are number of salts but sodium chloride is the most common among them.
  • Sodium chloride is also known as table salt or common salt. Sodium chloride is used to enhance the taste of food.
  • Most of the salts are crystalline solid.
  • Salts may be transparent or opaque.
  • Most of the salts are soluble in water.
  • Solution of the salts conducts electricity in their molten state also.
  • The salt may be salty, sour, sweet, bitter and umami (savoury).
  • Neutral salts are odourless.
  • Salts can be colourless or coloured.

Uses of Salts:

  • Sodium-Chloride is used in the manufacture of chlorine, caustic soda, washing soda and baking soda.
  • Ammonium salts are used as fertilizers.
  • Potassium-Nitrate is used in the manufacture of gun powder and fire-works.
  • Silver-Bromide is used in photography.
  • Potassium-Chlorate is used in the match industry.
  • Aluminum-Sulphate is used in preparing alums.

INDICATORS: 

  • Special type of substances are used to test whether a substance is acidic or basic.
  • These substances are known as indicators.Acid base indicators sukrajclasses.com
  • The indicators change their colour when added to a solution containing an acidic or a basic substance. Turmeric, China rose petals (Gudhal) and Litmus are some natural indicators. Natural indicators the indicators that occur in nature.
  • We cannot taste every object and find its nature. Therefore, we use indicators.
  • Acid turns blue litmus red and Base turns red litmus blue.

Acid Rain:

When the rain water has increased amounts of acids in it, it is called Acid Rain.

  • When pH of rain water is less than 5.6, it is called acid rain.
  • The main constituents of acid rain are Sulphuric Acid and Nitric Acid.
  • The acid rain is formed because of the presence of air pollutants such as Nitrogen dioxide, Carbon dioxide and Sulphur dioxide in the air.
  • These pollutants mix with the rainwater and form acids such as Nitric acid, Sulphuric acid and Carbonic acid respectively.
  • The acid rain in severely affect the vegetation, animal life and even buildings of the region where it falls.

PH Scale and Its Facts:

A scale for measuring hydrogen ion concentration (or strength of acid) in a solution, called pH scale.

  • The measure of acidity or basic nature of a substance can be determined by its pH value.
  • pH scale was discovered by P.L Sorenson.
  • The full form of pH is Potential of Hydrogen.
  • The pH value is generally determined by using pH strips or solutions.
  • The pH scale ranges from to 14.
  • The pH of a neutral solution is 7.
  • Values less than 7 on the pH scale represent an acidic solution.
  • pH value increases from 7 to 14, it represents a basic solution (increase in OH ion concentration).

 

PH-SCALE- sukrajclasses.com

 

       Substance                              PH Value

  • Stomach acid                           1.7
  • Lemon juice                              2.2
  • Vinegar                                     2.9 (2.4 – 3.4)
  • Soda                                         3.0
  • Wine                                         3.5 (2.8-3.8)
  • Beer                                          4.0-5.0
  • Coffee, black                             5.0 (4.5-5.5)
  • Urine                                         5.5-7.5
  • Saliva                                        6.5-7.5
  • Milk                                           6.9
  • Pure water                                7.0
  • Tears                                         7.4
  • Blood                                        7.3 to 7.5
  • Seawater                                  8.5
  • Milk of magnesia                      10.5
  • Ammonia solution                    12.5

Buffer Solutions:

The solutions which resist the change in its PH value on an addition of a small amount of acid or base are called buffer solutions.

  • Acidic buffer solution has PH value less than 7.
  • Basic buffer has PH value greater than 7.

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