Quick Notes

Quick Notes

Science Chapter 8: Acid and Alkali
8.1 Acid and Alkali
 
  • In simple a word, acidic substances have a sour taste and alkaline substances have a bitter taste.
 

8.1

Acid and Alkali
 
  • Each substance around us has its own chemical properties like acidic, alkaline and neutral. 
 

Acid, Alkaline and Neutral 
 
  • The acidity, alkalinity and neutrality of a substance can be tested using litmus paper. 
 
  • Litmus paper has two colours which are red and blue. 
 
  • The changes of the litmus paper colour and its indication:- 
 
Litmus Paper Blue  Red 
Acidic  Change to red Not change 
Alkaline  Not change  Change to blue
Neutral  Not change Not change
 
  • Examples of litmus paper test:- 
 
Materials Litmus paper Property
Vinegar  Blue→Red Acidic
Lemon juice Blue→Red Acidic
Detergent  Red→Blue Alkaline
Shampoo Red→Blue Alkaline
Water No change Neutral
 
 

Acidic, Alkaline and Neutral Substance
 
  • Acidic substances have a sour taste and sting when touched.
 
Examples of acidic substance:- 
  1. Lemon
  2. Tomato 
  3. Vinegar 
 
  • Alkaline substances have a bitter taste and smooth when touched. 
 
Examples of alkaline substances:- 
  1. Bittergourd 
  2. Detergent 
  3. Soap 
  4. Shampoo
 
  • Neutral substances usually have various taste such as tasteless, salty and sweet. 
 
Examples of neutral substance:-
  1. Salt 
  2. Sugar 
  3. Water 
  4. Oil 
 
  • The taste and texture of the substance are not scientific indicators for the properties of the substance. 
 
 

Acidic, Alkaline and Neutral Substance Around Us
 
  • Acidic and alkaline substance have multiples uses in our daily life. 
 
  • For example:-
 
 
 

Litmus Paper Substitutes
 
  • We can use other materials to test the acidity and alkalinity of substances. 
 
  • Natural substances that substitute litmus paper:-
 
Turmeric Juice 
Acidic  Alkaline
The yellow colour will not change The yellow colour will turn brown
 
Purple Cabbage Juice 
Acidic Alkaline
The purple colour will change to red The purple colour changes to blue
 
Hibiscus Juice
Acidic Alkaline
The red colour remains the same  The red colour changes to green