Calculating pH (needed for tomorrow) (1 Viewer)

[lachlan43]

I'm having trouble with the following question:

A sulfuric acid solution has a concentration of 5 x 10^-4 mol L-1

What is the pH of the solution, assuming the acid is completely ionised?

A)3.0
B)3.3
C)3.6
D)4.0

I calculated 3.3, but the Board of Studies has the answer as 3.0, so I need to know how they got to exactly 3.

I simply used -log 5 x 10^-4 which gave the answer 3.3, but obviously I'm wrong, so help please.

 

[adcarson]

im pretty sure when u do it that you have to find out the concentration of Hydronium ions (H30+) before u do the equation

 

[lachlan43]

How exactly do you do that?

Forgive my slowness when it comes to this.

 

[CJBrownie]

Sulfuric Acid is H2S04.... meaning there are 2 H+ ions.

So the [H+] = 2 x (5 x 10^-4) = 1 x 10^-3

ph = - log (10^-3)

ph = 3

 

[lachlan43]

Thank you! You have my respect.

 

[CJBrownie]

No problems.