Question

please answer both questions

QUESTION 22 What is the conjugate base of H2PO4 (aq)? а. НРОД2- b. НзР C. НЗРОД PO43 е, Нзо*

Answer 1

22)

Conjugate base is formed after acid looses H+

H2PO4- after loosing H+ forms HPO42-

So, HPO42- is conjugate base

Answer: a

23)

mol of HCl added = 0.089 mol

CN- will react with H+ to form HCN

Before Reaction:

mol of CN- = 0.303 M *1.0 L

mol of CN- = 0.303 mol

mol of HCN = 0.363 M *1.0 L

mol of HCN = 0.363 mol

after reaction,

mol of CN- = mol present initially - mol added

mol of CN- = (0.303 - 0.089) mol

mol of CN- = 0.214 mol

mol of HCN = mol present initially + mol added

mol of HCN = (0.363 + 0.089) mol

mol of HCN = 0.452 mol

Ka = 4*10^-10

pKa = - log (Ka)

= - log(4*10^-10)

= 9.398

since volume is both in numerator and denominator, we can use mol instead of concentration

use:

pH = pKa + log {[conjugate base]/[acid]}

= 9.398+ log {0.214/0.452}

= 9.073

Answer: d