[LukeeeeBennett]

The question is " Calculate the concentration, in mol dm
^–3
, of an aqueous solution of sulfuric acid
that has a pH of 0.25"

Now, I used [H+] = 10^-pH = 0.56, but the marking scheme says a second mark is then [H₂SO₄] = 0.5 x [H+] = 0.28.

I knew that [H+] wasn't = to [H₂SO₄], but I can't understand why it's half of the [H+]?

Can anyone guide me through this?

[sjb]

The question is " Calculate the concentration, in mol dm
^–3
, of an aqueous solution of sulfuric acid
that has a pH of 0.25"

Now, I used [H+] = 10^-pH = 0.56, but the marking scheme says a second mark is then [H₂SO₄] = 0.5 x [H+] = 0.28.

I knew that [H+] wasn't = to [H₂SO₄], but I can't understand why it's half of the [H+]?

Can anyone guide me through this?

Can you write equations for the disassociation of sulfuric acid?

[LukeeeeBennett]

H₂SO₄ = 2H⁺ + SO₄^-?

[sjb]

H₂SO₄ = 2H⁺ + SO₄^-?

OK, so what does the equation tell you? For every mole of sulfuric acid you put in, how many moles of H+ do you get out?

[AWK]

You can treat suphuric acid this way
H₂SO₄ = 2H⁺ + SO₄^2-
only at the concentrations close to 10^-4 or lower.
Otherways
H₂SO₄ = H⁺ + HSO₄^-
complete reaction

HSO₄^- = H⁺ + SO₄^2-
equilibrium reaction based on K₂ of H₂SO₄

[sjb]

You can treat suphuric acid this way
H₂SO₄ = 2H⁺ + SO₄^2-
only at the concentrations close to 10^-4 or lower.
Otherways
H₂SO₄ = H⁺ + HSO₄^-
complete reaction

HSO₄^- = H⁺ + SO₄^2-
equilibrium reaction based on K₂ of H₂SO₄

True enough, but at a high school level? What are your thoughts on the answer then?

[AWK]

c=([H₃O⁺]²+ K₂[H₃O⁺])/(2K₂+[H₃O⁺])