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ID: 556184 • Letter: C
Question
Copyright O McGraw-Hill Education. Permission required for reproducion or dispay TABLE 16.5 Ionization Constants ofsome weak Acids at 25°C Name of acid Formula Structure K, Chloroacetic acid Hydrofluoric acid Nitrous acid CH CICOOH HF HNO, CH,CI-C-0-H H-F 0=N-O-H 5.6× 10-2 7.1×10" 4.5 × 10" Formic acicd HCOOH H-C-0-H 1.7 x 10 Benzoic acid CH,COOH C-O-H 6.5 x 10 Acetic acid Hydrocyanic acid Phenol 1.8 × 10" 4.9 x 10-0 1.3 × 10" CH,COOH HCN C,H,OH 9) Which acid in the table above is the strongest? 10) Calculate the pH of a 05.00 x 10'M solution of phenol.Explanation / Answer
9)
for strongest acid, Ka should be largest
Ka is largest for CH2ClCOOH
So, CH2ClCOOH is strongest
10)
Lets write the dissociation equation of C6H5OH
C6H5OH -----> H+ + C6H5O-
0.5 0 0
0.5-x x x
Ka = [H+][C6H5O-]/[C6H5OH]
Ka = x*x/(c-x)
Assuming small x approximation, that is lets assume that x can be ignored as compared to c
So, above expression becomes
Ka = x*x/(c)
so, x = sqrt (Ka*c)
x = sqrt ((1.3*10^-10)*0.5) = 8.062*10^-6
since c is much greater than x, our assumption is correct
so, x = 8.062*10^-6 M
So, [H+] = x = 8.062*10^-6 M
we have below equation to be used:
pH = -log [H+]
= -log (8.062*10^-6)
= 5.09
Answer: = 5.09
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