Question

Tries remaining Pants out of 10 p u esto What is the pH of a solution of the buffer containing 0.004 M HCNO and 0.062 M NaCNO? The K of HCNO is 2.0x10-4 Multiple tries are permitted; however, 20% (1/5) point will be deducted for each incorrect response Answer: Check Question 14 What is the ratio of base to acid needed to obtain a pH of 4.51 for buffer containing HCSHENCI and CsH5N? The Ka of HC.HSN is 5.88x10-6 Multiple tries are permitted; however, 20% (1/5) point will be deducted for each incorrect response Answer: check HI 60%

Answer 1

13)

Ka = 2*10^-4

pKa = - log (Ka)

= - log(2*10^-4)

= 3.699

use:

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

= 3.699+ log {6.2*10^-2/4*10^-3}

= 4.889

Answer: 4.89

14)

Ka = 5.88*10^-6

pKa = - log (Ka)

= - log(5.88*10^-6)

= 5.231

use:

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

4.51 = 5.231+log {[C5H5N]/[HC5H5N+]}

log {[C5H5N]/[HC5H5N+]} = -0.7206

[C5H5N]/[HC5H5N+] = 0.1903

Answer: 0.190