mid term

I don't really understand question 2 on the 2006 midterm. When you ask "what is the charge change resulting from the incorporation of the Mg2+ instead of the Al3+" are looking for something about how it becomes acidic?? Does in become negative? Thanks a lot!

this is related to the isomorphic substitution. And in this example the substitution leads to formation of a negative charge. This is the same example as I used in the lecture.