Video Transcript
What color precipitate is formed
when a few drops of dilute NaOH are added to a salt or a solution containing a Cu2+
cation?
In this question, we want to know
what color copper(II) cations exhibit when forming a precipitate with NaOH, or
sodium hydroxide. A dilute sodium hydroxide solution
is a testing reagent when determining the presence of various cations. This is a useful testing reagent
because the reaction between hydroxide anions and many cations produce distinctive
precipitates.
The appearance of the precipitate
formed allows us to identify the cation in the unknown salt or solution. For example, iron(II) ions form an
iron(II) hydroxide precipitate that is pale-green in appearance. Iron(III) cations react to form an
iron(III) hydroxide precipitate that is red brown.
Aluminum, zinc, and calcium ions
all form their respective hydroxide precipitates, which all appear white. Chromium(III) ions form a
gray-green precipitate of chromium(III) hydroxide. Copper(II) cations react to form a
copper(II) hydroxide precipitate that is pale blue in appearance.
Therefore, the color of the
precipitate formed when a few drops of dilute NaOH are added to a salt or solution
containing a Cu2+ cation would be pale blue.
