Year 12s: what will be the first way you research your future options? >>

I don't get this question although it' worth one mark..haha.

Waste water from some industrial processes sometimes contains harmful metal ions, such as chromium ions. These ions must be removed from the water before it can be returned to the river.

A method of removing chromium ions (Cr³+) from water is represented in this equation.

(Cr³+) (aq) + 3OH- (aq) →Cr(OH)3 (s)

What type of substance would be added to the water to provide the OH– ions? [ 1 mark ]

Reply 1

Carm15796

Original post by JenieOh

Where do OH- ions come from basically is what its asking. They come from alkalis. An alkali release OH- ions into aqueous solution (acid releases H+ ions/protons). So I assume the answer would be alkali, and they arent looking for specifics.