Hydroxide ion (OH⁻)
- Charge
- −1
- Atoms
- O, H
- Atoms in total
- 2
- Mass of the ion
- 17.007 g/mol
Hydroxide is a single oxygen atom bonded to a single hydrogen atom, carrying a 1− charge. It is what is left when a water molecule loses a hydrogen ion, H⁺, while the bonding electrons stay behind on the oxygen. Hydroxide makes solutions basic, so you find it in drain cleaners, antacids and the limewater used to test for carbon dioxide.
- Hydroxide has no -ate or -ite ending; its name simply joins hydr(ogen) and oxide.
- When an acid neutralizes a base, hydronium and hydroxide combine to form water: H₃O⁺ + OH⁻ → 2H₂O.
- Sodium hydroxide, NaOH, also called lye or caustic soda, is used to make soap, paper and many other chemicals.