Strong and weak bases

"Strong" bases ionize completely in water.

Example: Sodium hydroxide, NaOH, is a strong base.

Bases are substances that releases hydroxide ions, OH^-, in water.

"Strong" bases ionize completely in water. For example,

The above reaction indicates that when sodium hydroxide reacts with water, hydroxide ions are produced in aqueous solution. Note that the arrow points to the products, indicating that virtually ALL the NaOH becomes Na+ and OH^- ions in aqueous solution. NaOH is therefore a strong base.

"Weak" bases ionize partially in water.

Ammonia, NH₃, does not completely ionize in water. Most of the ammonia in solution remains un-ionized and a small fraction ionizes to form OH^- and NH₄⁺ ions. To represent this in a chemical equation, a double arrow is used. The longer arrow pointing toward the reactants indicates that ammonia in solution remains un-ionized. NH₃ is classified as a weak base.

Examples

Names and formulae of eight strong bases.

• NaOH, sodium hydroxide
• LiOH, lithium hydroxide
• KOH, potassium hydroxide
• RbOH, rubidium hydroxide
• CsOH, cesium hydroxide
• Ca(OH)₂, calcium hydroxide
• Sr(OH)₂, strontium hydroxide
• Ba(OH)₂, barium hydroxide

Names and formulae of a weak base.

• NH₃, ammonia

Content suitability

BCIT courses: CHEM 0011