Sodium hydroxide (#NaOH#) is classified as a strong base. For every mole of sodium hydroxide added to a large volume of water, one mole of what ion enters the solution?

1 Answer
Jul 2, 2016

One mole of hydroxide anions, #"OH"^(-)#.


Strong bases are characterized by the fact that they dissociate completely in aqueous solution.

In this case, sodium hydroxide, #"NaOH"#, is classified as a strong base because it dissociates completely in aqueous solution to form sodium cations, #"Na"^(+)#, and hydroxide anions, #"OH"^(-)#.

You thus have

#"NaOH"_ ((aq)) -> "Na"_ ((aq))^(+) + "OH"_ ((aq))^(-)#

Since one formula unit of sodium hydroxide contains #1# sodium cation and #1# hydroxide anion, it follows that one mole will contain

  • one mole of sodium cations
  • one mole of hydroxide anions

So, your sodium hydroxide solution will contain sodium cations and hydroxide anions

From the perspective of an acid - base reaction, the sodium cations are of no importance to the solution. In fact, sodium hydroxide is used as way to deliver hydroxide anions to the solution.

You can thus say that every mole of sodium hydroxide dissolved in solution will produce one mole of hydroxide anions, which have a direct impact on the pH of the solution.