Transition metal in a salt

[Charlize Choo 1G]

Is CuSO4 acidic, basic, or neutral? How do we identify the solution when the salt has a transition metal?

[Emily La 2B]

CuSO4 is acidic. Cu 2+ is a transition metal is the +2 charge makes the solution slightly acidic. Transition metals of +2 and +3 charges tend to make the solution acidic. Since SO4 is the conjugate of a strong acid, it has a neutral charge. Therefore CuSO4 is acidic.

[Charlize Choo 1G]

Thank you! Just to clarify, normal Group 2 cations would be neutral but transition metals with 2+ charge are acidic?

[Emily La 2B]

Yes, group 1 and 2 cations are neutral in a solution, but transition metals tend to make the solution acidic due to their charges.

[Justin Selby 2G]

Hi,

In the case of CuSO4, the molecule will ionize into Cu2+ and SO4^2- in solution. SO4^2- is the conjugate base of the strong acid H2SO4, and any conjugate of a strong acid or base will not affect the pH of the solution, so the SO4^2- anion will not affect the pH of the CuSO4 solution.

Cu2+, on the other hand, is a transition metal cation with a relatively high charge (>2+ is generally considered a high charge but Cu2+ is also included in this category). Because of its high positive charge, it tends to bond with water molecules, taking the place of one of the H atoms in H2O. The Cu2+ ion will then result in a Cu--O--H molecule with two lone pairs around the O atom. The H atom that was replaced by the Cu2+ cation is now floating free in solution as H+ and will bond with another unaffected H2O molecule, producing H3O+. This is why the Cu2+ ion causes the solution to become acidic: because it bonds to a water molecule and causes the formation of H3O+, which is the very foundation of an acidic solution.

To determine whether a salt will produce an acidic, basic, or neutral solution, all you have to do is look at the ions produced by the salt in solution. Then, you determine whether the ions are conjugates of strong or weak acids/bases. If they are conjugates of a strong substance, they will not affect the pH of the solution. If they are conjugates of a weak substance, they will lead the solution to be whatever type of conjugate they are. For example, a salt that ionizes into a conjugate acid of a weak base will cause the solution to become acidic.

Hope this is helpful!