Strong acid / Weak base? How to determine??
Answer:
K2CO3 is a salt in which disgregative anions derived from diprotic acid, can be hydrolyze to a considerable extent.
CO32- + H2O <> HCO3- + OH-
Kh= Kw/KII = 1.00 x 10^-14 / 4.84 x 10^-11 = 2.07 x 10^-4
If CO32- is 0.150 M
pH = 11.7 so this strong salt is basic
Phosphoric acid is a weak acid :
H3PO4 <> H+ + H2PO4- KI = 7.5 x 10^-3
H2PO4- <> H+ + HPO42- KII = 6.2 x 10^-8
HPO4- <> H+ + PO43- KIII = 1 x 10^-12
if u wanna know if it is a strong/weak acid/base, u need to find out its pH (or pOH)
pH = -log[H+], it means the less pH is, the stronger acid it is.
pOH = 14 - pH = -log[OH-]
If substances have either a Ka or a Kb value that is less than or significantly less than 1, then they are weak acids or bases respectively. Phosphoric acid by definition is a weak acid, but is a much stronger acid than potassium carbonate is a base. A lot will also depend on concentration.
Your endpoint will most likely be in the 4-5 pH range, so you want an indicator which changes in that region and noticeably. There a lot to choose from in that region, but the most common is probably methyl red.
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