Strong Bases

In-depth explanation of Strong Bases

Strong bases, such as the hydroxides of the alkali metals and the heavier alkaline earth metals, dissociate completely in water to release hydroxide ions. For a monohydroxide base the hydroxide concentration equals the base concentration, so pOH is easy to calculate directly. Barium hydroxide releases two hydroxide ions per formula unit, so its hydroxide concentration is twice its molarity. Solubility limits how concentrated a solution can be made with calcium and magnesium hydroxides, which are only sparingly soluble. Strong bases are used in neutralization, soap making and as cleaning agents.

Going deeper: Strong Bases

Key ideas: Group 1 hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) and heavy Group 2 hydroxides Ca(OH)2, Sr(OH)2, Ba(OH)2 dissociate fully. [OH-] equals molarity times the number of OH groups, so 0.020 M Ba(OH)2 gives 0.040 M OH- and pOH 1.40, pH 12.60. Metal oxides and amides (O2-, NH2-) are even stronger and react completely with water.

Common mistakes and connections: Common error: forgetting the factor of 2 for Ba(OH)2 or Ca(OH)2. Limited solubility also matters: Ca(OH)2 saturates near 0.02 M, so very concentrated solutions cannot exist. Do not call Mg(OH)2 or Al(OH)3 strong bases; they are insoluble. Connect to Ksp.

Visualization of Strong Bases

Strong hydroxides of equal 0.010 M strength give pH 12, and Ba(OH)2 is higher because it releases two OH- per formula unit; weak NH3 is far lower. The interactive lesson shows this as a live animation or chart.

Worked example and use case

A 0.005 M Ba(OH)2 solution contains 0.010 M OH-, giving pOH 2.00 and pH 12.00.

Where Strong Bases fits in Acids, Bases & Electrochemistry

Strong Bases is topic 10 of 105 in Acids, Bases & Electrochemistry.

Related topics

• pH ScaleBeginner
• pOH and pKwBeginner
• Strong AcidsBeginner
• Weak AcidsIntermediate
• Weak BasesIntermediate
• Acid Dissociation ConstantIntermediate

Browse all 105 topics in Acids, Bases & Electrochemistry