ACIDS AND BASES

What are acids?
Acids are substances that produce hydrogen ions (H+) or hydronium ions (H₃O⁺ ) in solution.
For example: HCl +H₂O -----> Cl^- + H₃O⁺   

                 HCl -----> Cl^- + H⁺  

This is known as the Arrhenius concept for acids.

What is a base?

A base is a substance that can produce hydroxyl ions (OH^-) in solution.

For example: NaOH -----> OH^- + Na⁺  

This is known as the Arrhenius concept for bases.

There are other definitions for acids and bases. These include Bronsted-Lowry and Lewis concepts.

I will just discuss Bronsted-Lowry concept since it will help you identify some common acids/bases.

Bronsted-Lowry definition for acids: Acids are proton donors (H⁺ ) 
For example: Ammonium ion is an acid because it can donate a proton.  NH₄⁺ -----> NH₃ + H⁺

Bronsted-Lowry definition for bases: Bases are proton acceptors.

For example: Ammonia is a base because it can accept a proton. NH₃ + H⁺ -----> NH₄⁺

Exam tip: You should be able to identify common acids and bases.

Test for acids

Acids will turn blue litmus paper red.

Test for bases

Bases will turn red litmus paper blue.

pH scale 

The pH scale is used to indicate the strength of acids and bases. It is the negative log of the hydrogen ion concentration. The values range from 0 to 14 with 7 as the neutral point. pH of normal water is 7. From 0-7 is acidic and 8-14 is the the basic zone. The acidity increases from right to left and basicity increases from left to right. That is, a pH of 2 is more acidic than pH of 5, and pH of 13 is more basic than pH of 9.

Neutralization reactions

An acid will always react with a base to produce a salt and water. This is know as the neutralization reaction.

Example: HCl + NaOH ---------> NaCl + H₂O

Exam tip: You should be able to identify neutralization reactions.