Reactions of acids with hydroxides or oxides

Acids are sources of H+.  
 
Three common acids are HCl (hydrochloric acid), H2SO4 (sulfuric acid) and HNO3 (nitric acid).

Compounds having a metal cation (positively charged) combined with either oxide or hydroxide anion (negatively charged) are bases.  These compounds are proton (H+) acceptors.
 
Examples: 
NaOH (sodium hydroxide) 
Ca(OH)2 (calcium hydroxide)
MgO (magnesium oxide)
zinc oxide (ZnO).

The acid) donates H+ to the oxide or hydroxide ion from the base to give water.
OH– (hydroxide ion) accepts one H+ from an acid to give H2O (water).
O2– (oxide ion) accepts two H+ from an acid to give H2O (water).

Acids react with either hydroxides or oxides to give two products.

acid + metal hydroxide  salt + water
acid + metal oxide  salt + water
 
The salt is an ionic compound in which
the cation (positively charged) is the metal cation from the base. 
The anion (negatively charged) from from the the acid.
 
If the acid was sulfuric acid (H2SO4), the salt is a metal sulfate.  If the acid was hydrochloric acid (HCl), the salt is a metal chloride. 
If the acid was nitric acid (HNO3), the salt is a metal nitrate.
 
These reactions can be represented by word equations as shown below.

calcium hydroxide + sulfuric acid calcium sulfate + water

magnesium oxide + hydrochloric acid  magnesium chloride + water

zinc hydroxide + nitric acid zinc nitrate + water
Dr Sheila Woodgate
© The University of Auckland 2002