A 0.250 M solution of HCN has a pH = 4.87.

a) Determine the [H3O+] in the solution.

b) Calculate the percent ionization of HCN in this solution.

a. [H+]= 1.35x10^-5 M

b.5.4x10^-3%

Explanation:

a) pH= - log [H+]

[H+]= 10^-pH       [H+]= 10^-4.87    [H+]= 1.35x10^-5 M

b) HCN  -> H  + CN        at equilibrium  [H+]=[CN-]

0.250 M      -> 100%

1.35x10^-5 M ->x

x=(1.35x10^-5 M * 100)/0.250M

x=5.4x10^-3%

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.