When 1.00 mol of each compound below is dissolved in enough water to yield a 10.0 L solution, which solution contains the greatest concentration of ions?

A. `"K"_2"SO"_4`

`"K"_2"SO"_4` is a strong electrolyte. It ionizes completely in solution.

`underbrace("K"_2"SO"_4)_color(red)("1.00 mol/L") → underbrace("2K"^"+" + "SO"_4^"2-")_color(red)("3.00 mol/L")`

The concentration of ions is 3.00 mol/L.

B. `"H"_2"SO"_4`

`"K"_2"SO"_4` ionizes in two steps.

The first step goes to completion, but the second step does not.

`"H"_2"SO"_4 + "H"_2"O" → "H"_3"O"^"+" + "HSO"_4^"-"; K_1 = 3.0 ×10^3`
`"HSO"_4^"-" + "H"_2"O" ⇌ "H"_3"O"^"+" + "SO"_4^"2-"; color(white)(m)K_2 = 1.0 × 10^"-2"`

Thus, a 1.00 mol/L solution of `"H"_2"SO"_4` contributes 2 mol of ions from the first step plus some more from the second ionization.

For argument's sake, let's say that the concentration of ions is 2.1 mol/L.

C. `"H"_3"PO"_4`

`"H"_3"PO"_4` is a weak acid. It ionizes in three steps.

`"H"_3"PO"_4 + "H"_2"O" ⇌ "H"_3"O"^"+" + "H"_2"PO"_4^"-"; K_1 = 7.1 × 10^"-3"`
`"H"_2"PO"_4^"-" + "H"_2"O" ⇌ "H"_3"O"^"+" + "HPO"_4^"2-"; color(white)(l)K_2 = 6.3 × 10^"-8"`
`"HPO"_4^"2-" + "H"_2"O" ⇌ "H"_3"O"^"+" + "PO"_4^"3-"; color(white)(ml)K_3 = 4.2 × 10^"-13"`

Thus, a 1.00 mol/L solution of `"H"_3"PO"_4` contributes perhaps 0.5 mol of ions.

For argument's sake, let's say that the concentration of ions is 0.5 mol/L.

D. `"CH"_3"COOH"`

`"CH"_3"COOH"` is a weak acid.

`"CH"_3"COOH" + "H"_2"O" ⇌ "H"_3"O"^"+" + "CH"_3"COO"^"-"; K_text(a) = 1.76 × 10^"-5"`

It is weaker than phosphoric acid.

1 mol of acetic acid might contribute 0.05 mol of ions, so the concentration of ions is 0.05 mol/L.