A laboratory protocol calls for 1.00 L of a buffer at pH 9.00 using aqueous ammonia (…

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

Problem

A laboratory protocol calls for 1.00 L of a buffer at pH 9.00 using aqueous ammonia (

NH_3

) and ammonium chloride (

NH_4Cl

, molar mass = 53.5 g mol⁻¹). The stock solution available is 0.200 M

NH_3

, and the

pK_a

NH_4^+

is 9.25. If 750 mL of the

NH_3

stock solution is used and the final volume is adjusted to 1.00 L with water, what mass of

NH_4Cl

should be dissolved to prepare the buffer? (a)

8.0\text{ g}

(b)

14.3\text{ g}

(c)

20\text{ g}

(d)

9.6\text{ g}