Question

Equal amounts of chloride salts of the following metals in their highest oxidation states were prepared and their respective pH's measured. Which is the correct order of pH?

(Sn, Al, Cu, Ca, K)

A) Sn < Al < Cu < Ca < K
B) K < Ca < Cu < Al < Sn
C) Al < Cu < Ca < Sn < K
D) Sn < Al < Ca < Cu < K
E) K < Cu < Ca < Al < Sn

I know that binary acidic strength increases with increasing atomic number.

I'm thrown off by what it means by "highest oxidation states."

For reference, here are the atomic numbers:

Al - 13
K - 19
Ca - 20
Cu - 29
Sn - 50

Can anyone please provide an explanation?

Answer 1

Certain elements can have multiple oxidation states, like Cu which can be form 0 to 4+, same with Tin it can have up to 4+.

so if you had a salt, with Cu 4+, it'd be CuCl4

Answer 2

Okay, but does that really have an effect on what the question is asking?

I know in order to find pH, you take the negative log of the H+ ions present.

However, the question asks about chloride-based salts which don't contain Hydrogen at all.

Would I add the salt and water together, disassociate the salt and find the H+ concentration and take the -log of that to find the pH?

Answer 3

i don't think salts affect pH, i don't see how they could

Answer 4

Right... hmm I'm a bit lost.

I think it has something to do with the auto-ionization of water and conjugate acids and bases.

Answer 5

CuCl4 (s) + H20 (l) -> H4Cl(aq) + CuO (aq)

Doesn't seem quite right in that perspective :/

Answer 6

CuCl4 (s) + H2O (l) -> HCl(aq) + CuO2 (aq)

Answer 7

would it be 4 HCl (aq)

Answer 8

you wouldn't form HCl though, because they're ions (hence the subscript (aq)) in solution

Answer 9

i didn't balance it, but you wouldn't make HCl that way

Answer 10

unless you precipitated out OH, you wouldn't make more H3O+

Answer 11

Well since HCl is a strong acid and completely dissociates in water would this be a way to express it:

CuCl4 (s) + H2O (l) -> 4 H+(aq) + 4 Cl-(aq) + CuO2(aq)

Answer 12

hmm..

Answer 13

oh, Sn(OH)4 IS insoluble Ksp=1.0 x 10-57

meaning you would make more H+

Answer 14

Since the Oxygen from the OH is attracted to the Cu ions it leaves 4 H+ ions in the water? is that a way to determine the acidity?

Answer 15

yes exactly

Answer 16

which ever has the lowest Ksp (meaning least soluble) has the highest H+ increase, thus lowest pH

Answer 17

okay, so...

I would take the highest oxidation # for each of the metals and form a salt with chlorine and see how many H+ ions are left in water, to check for accuracy I can use the Ksp to determine relative pH?

Answer 18

Apparently Cu(OH)4 is not stable, and it only makes Cu(OH)2

Answer 19

well you wouldn't have to take into account the solubility of the hydroxide salts the would precipitate out of solution.

KCl wouldn't make any because KOH is fully soluble

Answer 20

you would*

Answer 21

so start by see in which are insoluble, those will have lower pH's, which ever has the lowest Ksp makes the most acidic solution