4.4        define acids as sources of hydrogen ions, H+, and alkalis as sources of hydroxide ions, OH¯

An acid is a substance that will create hydrogen ions in water.  

HCl(g) + (aq) → H+(aq) + Cl-(aq)

An alkali will create hydroxide ions in solution.

NaOH(s) + (aq) → Na+(aq) + OH-(aq)