Igcse Chemistry Revision NotesO Level Chemistry Revision Notes



An acid is a substance, which forms H+ ions. When dissolved in water, they can conduct electricity.

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HClArrow used In Chemical EquationH+     +    Cl

  • H+ ion is proton
  • Acids are called proton donors as provide H+   ions


General Properties:

  • Turns Blue Litmus Paper Red.
  • Acid reacts with Metals to produce Metal Salt + Hydrogen

Acid + MetalArrow used In Chemical EquationMetal Salt + Hydrogen

HCl + Mg Arrow used In Chemical EquationMgCl2   + H2

  • Acid react with bases to produce Metal Salt + Water

Acid + Metal Oxide / HydroxideArrow used In Chemical EquationMetal Salt + Water

  • Acid react with Carbonates to produce Metal Salt, water and Carbondioxide

Acid + Metal CarbonateArrow used In Chemical EquationMetal Salt  + Water  + Salt

HCl  + MgCO3Arrow used In Chemical Equation MgCl2    +  H2O    + CO2

Examples Of Common Acids:

Hydrochloric   Acid (HCl)  Sulphuric Acid ( H3PO4)  and Nitric Acid


  • Acids have sour taste
  • They have a pH value below 7.
  • Corrosive in nature. Lower the pH, more corrosive the acid becomes.
  • They dissolve in H2O to form solutions that conduct electricity.

Strong and Weak Acids:

Strong Acid:

An acid that is completely ionized in solution like;

HClArrow used In Chemical Equation H+     +    Cl

Other strong acids are Sulphuric and Nitric Acid H(NO3)2.

Weak Acid:

Partially ionizes in solution.

Some molecules remain unionized in solution like:

CH3COOHArrow used In Chemical Equation CH3COO–   +   H+

Other weak acids are Ethanoic, Carbonic and Sulphurous.


Distingiushing Between Weak And Strong Acid:

At the same concentration stronger acid would have the lowest pH.

The stronger acid, would be a better conductor of electricity at the same concentration.

At the same concentration and temperature, the stronger acid will react faster with solids.

All acidic properties are dependent upon the presence of H+ released by that acid. If no water is available, both organic and in organic acid will not release their H2 and finally they won’t show any acidic chemical reaction.

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