Ammonia (NH3 ) is a colorless gas with a strong pungent odor. When mixed with water (H2O), Ammonia will form a weak base. The term Ammonia refers to two chemical species which are in equilibrium in water. As the diagram represents, a phenolphthalein alcohol solution is used as an indicator in acid-base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions. The toxicity of ammonia is primarily attributable to the un-ionized form (NH3), as opposed to the ionized form (NH4 ). In general, more NH3 and greater toxicity exist at higher pH. When dissolved in water, normal ammonia reacts to form an ionized species called ammonium (NH4 ).