Bases and hydroxides
At this level, bases are metal hydroxides containing one or more OH− groups. Soluble bases are called alkalis. Their formulas, solubility, indicators, and reactions provide a practical system for recognition.
Learning goals
- Name bases and construct formulas from ion charges.
- Distinguish soluble alkalis from insoluble bases.
- Describe reactions with acids, acidic oxides, and heat.
- Explain common preparation routes and safe handling.
Formula and name
A base formula combines a metal cation with enough hydroxide ions to make total charge zero. Na+ needs one OH−, giving NaOH. Ca2+ needs two, giving Ca(OH)2. Name the metal followed by “hydroxide”; include a Roman numeral for variable-charge metals, as in Fe(OH)3, iron(III) hydroxide.
Solubility and indicators
Common alkalis include NaOH, KOH, and soluble portions of Ca(OH)2. Many other hydroxides are poorly soluble and may form precipitates. In aqueous alkalis, litmus turns blue and phenolphthalein turns pink. An indicator reports the solution environment; it does not identify the exact base.