Many hardware stores sell "muriatic acid" a 6 M solution of hydrochloric acid HCl(aq)to clean bricks and concrete. Grocery stores sell vinegar, which is a 1 M solution of acetic acid: CH₃CO₂H. Although both substances are acids, you wouldn't use muriatic acid in salad dressing, and vinegar is ineffective in cleaning bricks or concrete.

The difference between the two is that muriatic acid is a strong acid and vinegar is a weak acid. Muriatic acid is strong because it is very good at transferring an H⁺ ion to a water molecule. In a 6 M solution of hydrochloric acid, 99.996% of the HCl molecules react with water to form H₃O⁺ and Cl^- ions.

HCl(aq) + H₂O(l) H₃O⁺(aq) + Cl^-(aq)

Vinegar is a weak acid because it is not very good at transferring H⁺ ions to water. In a 1 M solution, less than 0.4% of the CH₃CO₂H molecules react with water to form H₃O⁺ and CH₃CO₂^- ions.

CH₃CO₂H(aq) + H₂O(l) H₃O⁺(aq) + CH₃CO₂^-(aq)

More than 99.6% of the acetic acid molecules remain intact.

Information provided by: http://chemed.chem.purdue.edu