Question

Which combination is the best choice to prepare a buffer with a ph of 9.0? which combination is the best choice to prepare a buffer with a of 9.0? nh3; nh4cl (pkb for nh3 is 4.75) hcho2; nacho2 (pka for hcho2 is 3.74) c5h5n; c5h5nhcl (pkb for c5h5n is 8.76) hno2;nano2 (pka for hno2 is 3.33)?

Answer 1

Answer:

$\boxed{\text{NH _{3} ; NH _{4} Cl}}$

Explanation:

The best choice to prepare a buffer of pH 9.0 is a conjugate acid/base pair in which the acid has pKₐ = 9.0 ± 1.

Let's examine each of the choices.

A. NH₃/NH₄Cl

For NH₃, = pK_b = 4.75

For NH₄⁺, pKₐ  14.00 - 4.75 = 9.25

B. HCHO₂/NaCHO₂  

For HCHO₂, pKₐ = 3.74

C. C₅H₅N/ C₅H₅NHCl

For C₅H₅N, = pK_b = 8.76

For C₅H₅N⁺, pKₐ  14.00 – 8.76 = 5.21

D. HNO₂/NaNO₂

For HNO₂, pKₐ = 3.33

The only acid with a pKₐ close to 9.0 is the ammonium ion.

The best buffer to prepare a buffer with pH 9.0 is $\boxed{\text{NH _{3} ; NH _{4} Cl}}$