Bud N. Chemist is performing a reaction in the chemistry lab for which he requir

Question

Bud N. Chemist is performing a reaction in the chemistry lab for which he requires 200 mL buffer solution with a pH of 10.5. The lab has the following chemicals:

0.1 M Hydrochloric acid (HCl)

0.1 M Acetic acid (CH3COOH)

0.1 M Hydrofluric acid (HF)

0.1 M Carbonic acid (H2CO3)

Baking soda (NaHCO3, molar mass = 84.01 g/mol)

Sodium Chloride salt (NaCl, molar mass = 58.44 g/mol)

Sodium bicarbonate (Na2CO3, molar mass = 106.00 g/mol)

Sodium acetate (CH3COONa, molar mass = 82 g/mol)

Relevant info:

Ka of CH3COOH = 1.8x10^-5

Ka of HF = 6.8x10^-4

H2CO3 : Ka1 = 4.3x10^-7 Ka2 = 5.6x10^-11

Create a solution reaction with the pH of 10.5 from the chemicals given.

Explanation / Answer

for getting pH = 10.5 value we need to choose nearer pKa value acid .

here we have carbonic acid H2CO3 Ka2 = 5.6 x 10^-11

pKa2 = 10.25

so we need two solutions NaHCO3 and Na2CO3 for making this buffer

here

pH = pKa2 + log [Na2CO3 /NaHCO3 ]

pH = 10.25 + 0.25

pH = 10.5

suitable buffer : NaHCO3 + Na2CO3

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