Acid, Bases and Salts

Start music   Jan 11 2017 || 12:59 PM

 

Acidic substances

  • The chemical nature of some substances is acidic
  • Eg: Curd, lemon juice, orange juice and vinegar
  • They taste sour

 

Name of acid

Found in

Acetic acid

Vinegar

Formic acid

Ant’s sting

Citric acid

Citrus fruits such as oranges, lemons, etc.

Lactic acid

Curd

Oxalic acid

Spinach

Ascorbic acid

Amla, Citrus fruits (Vitamin C)

Tartaric acid

Tamarind, grapes, unripe mangoes, etc.

 

Basic substances

  • The chemical nature of some substances is Basic
  • They taste bitter and feel soapy
  • Eg: Baking soda

 

Name of base

Found in

Calcium hydroxide

Lime water

Ammonium hydroxide

Window cleaner

Sodium hydroxide & Potassium hydroxide

Soap

Magnesium hydroxide

Milk of magnesi

 

Indicators

  • These are substances which are used to test whether a substance is acidic or basic
  • Eg: Turmeric, Litmus, China rose petals (all are naturally occurring indicators)

 

Litmus

  • Extracted from lichens
  • When added to an acidic solution, it turns red
  • When added to a basic solution, it turns blue
  • Available as solution or strips of paper, known as litmus paper
  • Solutions that do not change colour of either red or blue litmus are neutral solutions

 

China rose

  • Turns acidic solutions to dark pink (magenta)
  • Turns basic solutions to green

 

Acid rain

  • Rain becomes acidic because of air pollutants such as carbon dioxide, SO2 & NO2
  • They dissolve in rain water and become carbonic acid, sulphuric acid and nitric acid
  • Acid rain damages buildings, plant and animal life, monuments etc

 

Neutralisation

  • The reaction between an acid and a base is known as neutralisation.
  • In lab experiments, phenolphthalein is used as an indicator to detect neutralisation
  • Gives pink colour when in basic solution & remains colourless in acidic solution
  • Salt and water are produced in this process with the evolution of heat
    • Acid+Base Salt+Water (Heat is evolved)
  • Eg: Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) à Sodium chloride (NaCl) + Water (H2O)

 

Practical application of neutralisation:

Indigestion

  • Too much of acid in the stomach causes indigestion
  • To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide
  • It neutralises the effect of excessive acid.

 

Ant bite

  • When an ant bites, it injects formic acid into the skin
  • Effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate

 

Soil treatment

  • Plants do not grow well when the soil is either too acidic or too basic
  • Excessive use of chemical fertilisers makes the soil acidic
  • The soil is then treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide)
  • If the soil is basic, organic matter is added to it.
  • Organic matter releases acids which neutralises the basic nature of the soil

 

Factory wastes

  • The wastes of many factories contain acids
  • They are neutralised by adding basic substances