Question

A chemistry graduate student is given 125. ml. of a 1.80 M hydrocyanic acid (HCN) solution. Hydrocyanic acid is a weak acid with K-49x10". What mass of KCN should the student dissolve in the HCN Solution to turn it into a buffer with pH9.877 You may assume that the volume of the solution doesn't change when the kcn is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits.

Answer 1

PLUUN pH of a solution containing a weak given by - in contaming a weak and How and its salt keni pH = pka +log Chemin —> Nowy ka = 4.9810-10 - pka =- wg ka Log (4,9x10-10) - 9.31 Ni bora 10 This from en we get to loosoport to P os 9.87 = 9.31+ wg CR pour l a protes o3 wg IRON = 0.56 kb bora os trein = 100:56 all [leen) = 6,54 M 2 Now volume of the solar nomi b os 125 mL of 6.54 m KeN = 125x10 34 x 6.54 mole of kin 6 & 6 2.0 - 0.8175 mol of ken 1.8 Moloro mom of ken = 65.12 gmott. (Literature vulne). 20.8125 ml KIN = 0.8177 molx 65.12 g moke of kon - 53.24 g of Ken 2. 53.24g of K CN it requered. Ton Baron BOOTD