Chemistry Forum

Determine whether each of the following 1 M solutions is acidic, basic, or neutral.
a.NaHS
b.NaBr
c.NH₄Ac (remember Ac = acetate)
d.KNO₂
e.KHSO₃
f.NaH₂PO₄

I am working on these questions.

What are strong acid, base and weak acid, base. What are the corresponding species in every example?

All the 1 M aqueous solutions of the substances in the questions a, b, c, d, e, f are acidic.

No
A. Alkaline, B. Neutral C. Neutral, D. Alkaline, E. Acidic, F. Acidic

Explain why.: in A compare NaOH and H₂S
The same in the other questions

You are correct. Answer for question a is alkaline. Following is my chemistry work.

I computed the pH of 1.0 M solution of NaHS as follows:- NaHS + H₂O ⇌ NaOH + H₂S

\(K_a of HS = 1.2e-13 = \frac{[NaOH])[H_2S]}{[1.0M]}\) Concentration of H₂S is =\(\sqrt{1.2e-13}=[3.46e-7] \) We got concentration of H₂S. Ionization of H₂S is

H₂S ⇌ H⁺ + HS

\(K_a of H_2S = 8.9e-8 = \frac {[H^+][1.0M ]}{[3.46e-7]}=3.08e-13\) Hence pH of 1.0 M solution of NaHS=-log(3.08e-13)=12.51.

Hence the solution is alkaline.

Is my computation of pH correct?

Yes correct

Your answer to question e for pH of 1 M solution of KHSO₃(Potassium Hydrogen Sulfite) is acidic.
But my pH computation work result is different.

KHSO₃ + H₂O ⇌ H₂SO₃ + KOH

\(K_a = \frac{K_w}{K_b}= \frac{1e-14}{1.5e-2}=\frac{x\cdot x}{1 M}= 6.66e-13,x= 8.16e-7,pOH=6.088,pH=7.911 \) So, the 1 M solution of KHSO₃ is alkaline.

What is wrong with this pH computation?

Used wrong formula H₂SO₃ is a middle strong acid. pKa₁ is 1.8 pka2 is 7.

pH =( pk1 + pk2)/2

pH =(1.8 +7)/2 = 4.4