Moles to pH

[Vigo]

Does anyone know a conversion of the molarity of an acid to it's pH or a place where there is a table with this information?

[AL]

If it's a monoprotic strong acid, pH is just -log(molarity). If it's a weak acid, you'll have to look up its Ka to find [H+] and calculate pH as -log[H+].

[Vigo]

What molarity or acid would constitute a weak acid in this equation? I have 3 and 6 mol nitric, hydrochloric, and sulfuric and I may need to reduce the molarity in some cases to get the desired pH.

[silkworm]

All of those are strong acids. Sulfuric is diprotic so the dissociation of the second hydrogen has a Ka, but its works out to not being too important when calculating pH in practical applications.

 

Molarity doesn't determine how weak or strong an acid is, but the molarity of a strong acid does affect pH. Meaning, the more of a strong acid per liter of water, the lower the pH. A strong acid is a strong acid because it gives up it's proton readily in aqueous solution. Basically, as much HCl as you put into solution is as much H+ you're going to get.

 

A weak acid doesn't give up this proton as readily. Meaning, you're going to get less H+ than as much you put in.

 

I hope that helps.

 

Also, note that you have 3 and 6 moles of these acids. You're going to need molarity which is the moles/liters of water.

[Vigo]

Ok thanks. It helps a lot.