Class 7 Chapter 5 Science Acids, Bases and Salts Notes (NCERT)
0 likes1,325 views
The document explains the classification of substances as acids, bases, or neutrals, along with indicators used to test these properties. It covers topics such as acid rain, neutralization reactions, and practical applications of acids and bases in daily life, including indigestion and soil treatment. Additionally, it lists common acids and bases with examples of their sources.
Class 7 Chapter 5 Science Acids, Bases and Salts Notes (NCERT)
- 1. 1) Substances which are sour-> Acid, Substances which are bitter-> Base, Substances which are neither sour nor bitter-> Neutral 2) Substances which are used to test whether a substance is acid or base-> Indicator. Indicators change their colour when added to a substance with an acidic or basic nature- > i) Litmus-> Obtained from lichens, Most commonly used, Has a mauve(purple) colour in distilled water, Turns into blue in base and red in acid, Available in paper form-> Blue litmus paper, Red litmus paper. Acid Base Neutral Tastes-> Sour Bitter(except Coffee) Neither sour nor bitter Feeling-> Non-soapy Soapy Can be Non-soapy and soapy Contains-> H+ (Hydrogen) ions) OH- (Hydroxide ions) No specific ions Turns Litmus-> Red or Blue to Red Red or Blue to Blue No change Turns Turmeric to-> Yellow Reddish- Brown No change Turns China Rose to-> Dark Pink(Magenta) Green No change Turns Phenolphthalein to -> Colourless Pink No change Turns Methyl Orange to-> Red Yellow No change Nature-> Acidic Basic Neutral
- 2. ii) Turmeric-> Used as a spice, Turns red in base, To detect acid->use the turmeric used to test base. If turns back to yellow, It is an acid. iii)China Rose(Gudhal)-> Turns Magenta in Acid, Turns Green in base. 3) Acid Rain-> Rain containing excess of acids. It becomes acidic as pollutants like CO2(Carbon dioxide), NO2- (Nitrogen Dioxide), SO2(Sulphur dioxide) dissolve in rain to form H2CO3(Carbonic acid), HNO3(Nitric Acid), H2SO4(Sulphuric acid). It causes damage to buildings, historical monuments, plants and animals. 4) The reaction between an acid and a base which forms salt, water and evolved heat is known as neutralization. In this process, the acidic and basic of both solutions get destroyed. Acid+Base Salt+Water+Evolved heat. For eg.-> HClHydrochloric Acid+NaOHSodium Hydroxide NaClSalt+ H2OWater. 5) Neutralisation in our life-> a) Indigestion-> Stomach uses HCl(Hydrochloric Acid) to kill microbes in our food. When HCl is released in excess, it causes indigestion. To relieve pain, we use antacids (Substances which are used to neutralize the effect of acid) to neutralize the acid. For eg-> Milk of Magnesia which contains Mg(OH)2 (Magnesium Hydroxide). b) Ant sting-> When ant stings, It releases Formic Acid(CHOOH). To relieve irritation, we use Moist Baking Soda(NaHCO3) or calamine solution which contains ZnCO3(Zinc Carbonate).
- 3. c) Soil Treatment-> Chemical fertilisers make soil acidic. We treat the soil with CaO2(Calcium oxide or Quick Lime) or Ca(OH)2(Calcium Hydroxide or Slaked Lime). If the soil is too basic, we use compost as it releases acid. d) Factory wastes-> Factory wastes are to be treated before being released into water bodies as it may have acids which could kill fish. Thus, We use bases to prevent this. 6) Common Acids and bases-> Name of Acid Found in Acetic Acid Vinegar Ascorbic Acid (Vitamin C) Citrus Fruits, Amla Citric Acid Citrus Fruits Formic Acid Ant’s Sting Lactic Acid Curd Oxalic Acid Spinach Tartaric Acid Tamarind, Unripe Mangoes, Grapes Name of Base Found in Ammonium Hydroxide Window cleaner Calcium Hydroxide Lime Water Magnesium Hydroxide Milk of Magnesia Sodium Hydroxide and Potassium Hydroxide Soap