Textbook 6B.5

[Antonia Valencia 2H]

Hi! I was wondering why for #c of this problem in order to calculate the pOH of 0.0092 M Ba(OH)2, we must primarily multiply this value by 2 before taking the -log of it. Is it because the base is (OH)2? If so, what would be the equivalent of such a thing for an acid? Would it be something like H2? Thanks so much for the help!

[Jessica Phung 1E]

Yes, for this problem, you need to do one stoichiometric equation in order to find the concentration of OH because that's how the equation will be balanced (with 2 as its coefficient). For acids, it would depend on how many protons are actually being transferred. For example if there was like an H2, the acid could be polyproctic. For most cases however, it'll only be one transfer of a proton at a time meaning you wouldn't have to multiply.

[Triston Dinh 1D]

Hi,
For this problem, since Ba(OH)2 is a strong base, it would fully dissociate. When it dissociates, the result would be one mole of Ba+ and two moles of OH-. Stoichiometrically, since you know that one mole of Ba(OH)2 produces 2 moles of OH-, you would need to multiply the concentration of Ba(OH)2 by two in order to find the concentration of OH-. Once the concentration of OH- is found, you can then simply calculate for the pOH by taking the -log of this value.