Question

When either chlorine or hydrogen chloride is passed over a heated metal M, the same chloride is produced. An aqueous solution of this chloride is acidic. Which one of the following could be M?

A: Al
B: Ba
C: Cu
D: Fe
E: Na

Ans: A
Help w explanation please! Thanks!

Answer 1

Poor question. NaCl is the only one of those listed that would not be, at least slightly, acidic.
AlCl3, BaCl2, CuCl2 and FeCl2 all would be at least slightly acidic. AlCl3 would be the most acidic because it's a more active metal than the others. Why are they acidic? Becasue they hydrolyze with H2O. Al as follows:
AlCl3 + 3HOH ==> Al(OH)3 + 3HCl.
It's easier to write this way but it is more accurate to depict it as
Al(H2O)6(^3+ charge) + H2O ==> H3O^+ + Al(H2O)5(OH^-)^2+