5 ms·

So is this 0.2 pH more corrosive/stronger than sulfuric acid or not?

by 21 9y ago

hbk1966 9y ago
It is stronger
zzazzdsa 9y ago
Well, pH refers to the concentration of protons in water solvent. Since pure sulfuric acid has no water (excluding that which is in equilibrium with sulfur trioxide), pH isn't really well defined for it. A better definition of acidity which does not have this problem is the Hammett acidity function. Sulfuric acid on this scale has an acidity of -12. (Note that this acidity score is not fully comparable to pH. However, with a difference so massive (a factor of one trillion times more acidic), this subtle difference ceases to be relevant.) If you're asking about corrosivity, sulfuric acid gets its reputation because its also strongly dehydrating. Thus, it does wonderful things like rip the water out of your skin or char paper. I would hazard a guess that the water they've found in the paper does neither of those things.
- wfunction 9y ago
  I thought pH = -log[H+]? where [H+] is the molarity of the hydrogen ion? That doesn't involve water in the definition... what is the definition you're referring to? Edit regarding your reply asserting water is necessary (I can't reply now due to throttling): What about all the acid/base reactions that don't involve water? You can't ascribe any pH to either of them in that case?
  - Pulcinella 9y ago
    [H+] is shorthand for [H3O+]. H3O+ (hydronium ion) requires water plus a hydrogen ion from the acid. There aren't actually free H+ ions floating around. They are all attached to water molecules.
    - yogipatel 9y ago
      That's the definition of p[H]. The definition of the "real" pH is the -log of H+ activity. H+ activity is the concentration of H+ * a coefficient. In practice, the coefficient is considered to be 1, however there are cases (such as extreme concentrations) when that approximation isn't valid.
      - Pulcinella 9y ago
        Ah yes I had forgotten about activity. :)
gus_massa 9y ago
From: https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/s/Sulfuric_acid.htm https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/s/Sulfur... * 98%, concentrated (pH about 0.1) [This 98% is what you usually buy in a bottle to use in a chemistry laboratory.] * 33.5%, battery acid (used in lead-acid batteries) (pH 0.5)

So is this 0.2 pH more corrosive/stronger than sulfuric acid or not?

by 21 9y ago

So is this 0.2 pH more corrosive/stronger than sulfuric acid or not?

hbk1966 9y ago

It is stronger

zzazzdsa 9y ago

Well, pH refers to the concentration of protons in water solvent. Since pure sulfuric acid has no water (excluding that which is in equilibrium with sulfur trioxide), pH isn't really well defined for it. A better definition of acidity which does not have this problem is the Hammett acidity function. Sulfuric acid on this scale has an acidity of -12. (Note that this acidity score is not fully comparable to pH. However, with a difference so massive (a factor of one trillion times more acidic), this subtle difference ceases to be relevant.) If you're asking about corrosivity, sulfuric acid gets its reputation because its also strongly dehydrating. Thus, it does wonderful things like rip the water out of your skin or char paper. I would hazard a guess that the water they've found in the paper does neither of those things.

wfunction 9y ago
I thought pH = -log[H+]? where [H+] is the molarity of the hydrogen ion? That doesn't involve water in the definition... what is the definition you're referring to? Edit regarding your reply asserting water is necessary (I can't reply now due to throttling): What about all the acid/base reactions that don't involve water? You can't ascribe any pH to either of them in that case?
- Pulcinella 9y ago
  [H+] is shorthand for [H3O+]. H3O+ (hydronium ion) requires water plus a hydrogen ion from the acid. There aren't actually free H+ ions floating around. They are all attached to water molecules.
  - yogipatel 9y ago
    That's the definition of p[H]. The definition of the "real" pH is the -log of H+ activity. H+ activity is the concentration of H+ * a coefficient. In practice, the coefficient is considered to be 1, however there are cases (such as extreme concentrations) when that approximation isn't valid.
    - Pulcinella 9y ago
      Ah yes I had forgotten about activity. :)

gus_massa 9y ago

From: https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/s/Sulfuric_acid.htm https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/s/Sulfur... * 98%, concentrated (pH about 0.1) [This 98% is what you usually buy in a bottle to use in a chemistry laboratory.] * 33.5%, battery acid (used in lead-acid batteries) (pH 0.5)