A buffer is prepared by dissolving 0.50 g of benzoic acid (

CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases

Problem

C_6H_5COOH

, molar mass = 122 g·mol

^{-1}

) and 0.75 g of sodium benzoate (

C_6H_5COONa

, molar mass = 144 g·mol

^{-1}

) in water to make 250 mL of solution. Given that the

pK_a

of benzoic acid at 25 °C is 4.20, what is the pH of the buffer? (a)

4.20

(b)

4.30

(c)

4.10

(d)

4.35