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)?

From the given options, the best combination to prepare a buffer with a PH of 9.0 is given by;

Option 1; NH₃;NH₄Cl

Now, we want to find the best choice to prepare a buffer of pH 9.0. Thus, let us look at each option;

Option 1; NH₃;NH₄Cl

We are given that pK_b for  NH₃ is 4.75

Thus pKₐ for NH₄ is;

NH₄; pKₐ = 14.00 - 4.75

NH₄; pKₐ = 9.25

Option 2; HCHO₂; NaCHO₂  

We are given that pK_a for HCHO₂ is 3.74

HCHO₂; pKₐ = 3.74

Option 3; C₅H₅N; C₅H₅NHCl

We are given that pK_b for C₅H₅N is 8.76

Thus  

For C₅H₅N, = pK_b = 8.76

Thus, pKₐ for C₅H₅N is;

C₅H₅N; pKₐ = 14.00 – 8.76

C₅H₅N; pKₐ = 5.21

Option 4; HNO₂;NaNO₂

We are given pKₐ for HNO₂ as 3.33

HNO₂; pKₐ = 3.33

Looking at all the pKₐ values, the only acid that has a pKₐ close to 9.0 is NH₄ with a pKₐ of 9.25.

In conclusion, the best combination to prepare a buffer with pH of 9.0 is

NH₃;NH₄Cl

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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