thanks Dr.Bob, I got that question. I also have another question that I am having trouble on.

Question

I am being asked to arrange the oxides in each of the following groups in order of increasing basicity:
(a) K2O, Al2O3, BaO
(b) CrO3, CrO, Cr2O3

I know the answers are (a)Al2O3 < BaO < K2O and (b) CrO3 < Cr2O3 < CrO but I do not understand why these are the answers. How do you get these answers?

Thanks

Answer 1

I look at the acid strengths. Two rules you can remember is that acidity increases from left to right in the periodic table (due to electronegativity) in the same row and from top to bottom in the same column (due to size). So the left side elements (oxides in this case) form stronger bases and the right side oxides form stronger acids. For oxoacids, the stronger acid belongs to the compound (same central element) with more oxygen atoms; i.e., HClO < HClO2 < HClO3 < HClO4.
H2SO3 < H2SO4
HNO2 < HNO3
etc.