Would a benzoic acid/sodium benzoate buffer system be an appropriate choice if I

Question

Would a benzoic acid/sodium benzoate buffer system be an appropriate choice if I needed to maintain a pH of 8.5? Arsenic acid, H_2ASO_4 is a diprotic acid. The acid ionization constants are K_a1 = 5.5 times 10^5, k_a2 = 1.7 times 10^7, K_a3 = 5.1 times 10^13 Write the stepwise ionization equilibria for arsenic acid. Determine for a 0.350 M solution of arsenic acid the pH, and the equilibrium concentrations of all species (H_3ASO_4, H_2ASO_4^-, HASO_4^2-, ASO_4^3-, H_3O^+, OH^+) Clearly explain why HOCl is stronger than HOBr, whereas HCI is weaker than HBr with respect to acid strength Rank the conjugate bases of these acids in order of increasing base strength: HOCI, HBr, NH4+, HS-. Clearly explain you ranking

Explanation / Answer

Q[3]

would benzoic acid + sodium benzoate buffer be appropiate for pH = 8.5

NOT really, since pKa = 4.2

which is the average pH value of the buffer

acccording to

pH = pKa + log(A-/HA)

where

A- = benzoate

hA =benzoic acid

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