[steph_r]

Hi everyone,
I was having a look at this question in my chem book and found it a little confusing..

Question: Explain why the pH of a 1.0M solution of Hydrochloric acid is greater than the pH of a 1.0M solution of sulfuric acid

My attempt: I would have thought that HCl acid is a stronger acid and therefore, would have a smaller pH (more acidic) than sulfuric acid  ..

Help woudl be greatly appreciated ..

[Astrokel]

hey steph_r!

nono, why do you think HCl is a stronger acid? This question can actually be done intuitively, since the concentration of the acids are the same. Otherwise, you can calculate the concentration of H+ ions, thus the pH.

[steph_r]

Yes, i see where you're coming from, but how would you actually explain it? How do you explain that HCl has a greater pH than sulfuric acid?

[sameeralord]

Yes, i see where you're coming from, but how would you actually explain it? How do you explain that HCl has a greater pH than sulfuric acid?

A strong acid ionises more fully. So Ka value would be higher as more H30+ is produced. Look at the Ka tables for acids if you don't want to use formulas to work it out.

[Astrokel]

hey

can you show that 1.0M of HCl is less acidic than 1.0M of H₂SO₄? Therefore concluding, HCl has higher pH since it is less acidic.

[yukiheart]

hello all!!!

HCl ---> H⁺+ Cl-
1,0         1,0M

but
H2SO4 ------> 2H⁺+ SO4^2-
1,0                    2.0M

then pH[HCl] > pH[H2SO4]
note
HSO4- -------> H+ + SO4^2-  not all 100%

[MikeS]

Yuki just answered the question perfectly. All I can add is that the reason why H2SO4 can almost ionize both of its protons is because of the stability of the HSO4- and the SO4 2- ion due to resonance.

[AWK]

Yuki just answered the question perfectly. All I can add is that the reason why H2SO4 can almost ionize both of its protons is because of the stability of the HSO4- and the SO4 2- ion due to resonance.

H2SO4 ionizes its second proton in about 70 %.