QUESTION 17 If the pKa of HCHO 2 is 3.74 and the pH of an HCHO 2 /NaCHO 2 soluti

Question

QUESTION 17

       If the pKa of HCHO2 is 3.74 and the pH of an HCHO2/NaCHO2 solution is 3.74, which of the following is TRUE?

       [HCHO2] > [NaCHO2]

       [HCHO2] < <[NaCHO2]

       [HCHO2] < [NaCHO2]

       [HCHO2] = [NaCHO2]

       It is not possible to make a buffer of this pH from HCHO2 and NaCHO2.

4 points

QUESTION 18

       The equilibrium constant is given for one of the reactions below. Determine the value of the missing equilibrium constant.

         H2(g) + Br2(g) 2 HBr(g) Kc = 3.8 × 104

         2 HBr(g) H2(g) + Br2(g) Kc = ?

QUESTION 19

       The molar solubility of ZnS is 1.6 × 10-12 M in pure water. Calculate the Ksp for ZnS.

Explanation / Answer

17)   [HCHO2] = [NaCHO2]

pKa = 3.74

pH = 3.74

pH = pKa + log [salt /acid]

3.74 = 3.74 + log [NaCHO2/HCHO2]

[NaCHO2/HCHO2] = 1

NaCHO2 = HCHO2

18) Kc = 2.6 x 10^-5

H2(g) + Br2(g) 2 HBr(g) Kc = 3.8 × 10^4

2 HBr(g) H2(g) + Br2(g)

Kc = 1 / 3.8 × 10^4

Kc = 2.6 x 10^-5

19)

ZnS -------------------> Zn+2 + S-2

S S

Ksp = [Zn+2][S2-]

1.6 × 10^-12 = S^2

S = 1.26 x 10^-6 M

molar solubility = 1.26 x 10^-6 M

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