More Chem Ch. 8 Help!?

A.) [H3O+] = 4.0×10−8 M
B.) [H3O+] = 6.0×10−6 M pH = -log (6.0*10^-6) pH = 5.22
C.) [OH−] = 6.0×10−2 M : H3O+ = 10^-14/(6.0*10^-2) = 1.67*10^-13: pH = -log( 1.67*10^-13) = 12.78

You should have no problem in following the above to get the answers to the following three:
D.) [OH−] = 6.0×10−3 M
E.) [H3O+] = 5.1×10−2 M
F.) [OH−] = 4.1×10−6 M

Which of the following represent a buffer system? (Check All That Apply)


B.) H2CO3 and NaHCO3
C.) HF and KF
are buffers.

Problem:
A.)
pH = -log[H₃O⁺] = -log(4 × 10⁻⁸) = 7.4

B.)
pH = -log[H₃O⁺] = -log(6 × 10⁻⁶) = 5.2

C.)
pOH = -log[OH⁻] = -log(6 × 10⁻²) = 1.2
pH = 14.0 - pOH = 14.0 - 1.2 = 12.8

D.)
pOH = -log[OH⁻] = -log(6 × 10⁻3) = 2.2
pH = 14.0 - pOH = 14.0 - 2.2 = 11.8

E.)
pH = -log[H₃O⁺] = -log(5.1 × 10⁻²) = 1.3

F.)
pOH = -log[OH⁻] = -log(4.1 × 10⁻⁶) = 5.4
pH = 14.0 - pOH = 14.0 - 5.4 = 8.6


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Which of the following represent a buffer system?

A buffer solution is a mixture of a weak acid and its conjugate base or a mixture of a weak base and its weak acid.

A.) No
OH⁻ in NaOH is a strong base.

B.) Yes
It is a mixture of a weak base CO₃²⁻ and its conjugate acid HCO₃⁻.

C.) Yes
It is a mixture of a weak acid HF and its conjugate base F⁻.

D.) No
Cl⁻ is the conjugate base of the strong acid HCl.

...... The answers are: B.) and C.)