prediction factor in how reactions occur. Model 1 There are many ways that acids and bases have been defined over history. Two of these definitions are Arrhenius and Brnsted-Lowry. In 1903 Svante Arrhenius won the Nobel Prize in Chemistry for defining acids and bases in terms of the ions produced in water. The definitions of Arrhenius acids and bases are provided below: Acid - a substance that yields H*(aq), hydrogen ions (or hydronium ions, HO*(aq)) as positive ions in aqueous solution. Base - a substance that yields OH-(aq), hydroxide ions as negative ions in aqueous solution. Neutral solution - contains hydrogen (or hydronium) ions and hydroxide ions in equal concentrations. Spectator ions present in acidic and basic solutions, but do not participate in the neutralization reaction between the H*(aq) (hydrogen ions) and OH- (aq) (hydroxide ions). Spectator ions can be positive or negative, and they are present in quantities needed to produce electrically neutral solutions. Key - H+ ions OH ions HO A