Chemistry Notes on Acids and Base

Arrhenius concept of acids and bases:

• Acid is a substance which produces hydrogen ions (H⁺) in aqueous solution e.g. HCL (H⁺ Cl^-), Sulphuric Acid, H₂SO₄ (2H⁺ SO^2-₄).
• Base is a substance which produces Hydroxide ion (OH^-) in aqueous solution e.g. sodium hydroxide and ammonium hydroxide etc.

Bronsted Lowery concept of Acids and Bases

• An acid is a molecule or ion which is capable of donating a proton.
• A base is a molecule or ion which is capable of accepting a proton.

Lewis concept of Acids and Bases

• An acid is a substance which can accept an electron e.g. boron fluoride (BF₃) and carbon dioxide.
• Base is a substance which can produce an electron e.g. fluoride (F^-) and chloride (Cl^-).

Some important acids and their presence

These acids are mostly asked in SSC Exams. Don't forget to remember this table.

PH Scale

• PH value is a measure of the acidity or basicity of an aqueous solution.
• Solution with PH value less than 7 is considered as acidic.
• Solution with PH value greater than 7 is greater 7 is considered as basic.

PH values of some important solutions.

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.
• PH value of blood is maintained with the help of H₂CO₃/HCO₃ buffer in spite of many acidic foods we eat.

Salts:

• When acidic and basic solutions are mixed in proper proportion than their own nature is destroyed and Salt is formed.
• Acid turns blue litmus red and base turns red litmus blue.
• Formation of salts after mixing base and acidic is called a neutralisation reaction.

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