Question

A. The pH of an aqueous solution of 0.345 M hydrocyanic acid is ____

B. The pH of an aqueous solution of 0.345 M triethanolamine (a weak base with the formula C₆H₁₅O₃N) is ____.

C. The pH of an aqueous solution of 0.221 M ammonium iodide, NH₄I (aq), is ______.

This solution is _________(acidic,basic,neutral)

D. A buffer solution is 0.315 M in H2S and 0.258 M in . If Ka1 for H2S is 1.0 x 10^-7, what is the pH of this buffer solution?

pH = ________

Please answer all, if not as many as possible! Thank you (:

Answer 1

(a)

HCN = H+ + CN-

Ka for HCN = 5*10^-10

Therefore, Ka = [H+][CN-]/[HCN]

[H+]=[CN-]=X , [HCN]=0.345-X at equilibrium

Therefore, Ka = [X][X]/[0.345-X]

X is very small, so ignore X

Ka = X^2/0.345

5*10^-10 = X^2/0.345

(5*10^-10)*0.345 = X^2

1.725‬*10^-10 = X^2

X = 1.31*10^-5

[H+]= 1.31*10^-5

We know that,

pH = - log [H+]

pH = -log (1.31*10^-5)

pH = 4.88

(b)

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