27. Which one of the following is NOT amphoteric? [A] Zn(OH) 2 [B] Sn(OH) 2 [C]

Question

27. Which one of the following is NOT amphoteric?

   [A] Zn(OH)2 [B] Sn(OH)2 [C] Ca(OH)2 [D] Cr(OH)3 [E] Al(OH)3  

   28. Which below best describe(s) the behavior of an amphoteric hydroxide in water?

[A] With both conc. aq. NaOH and conc. aq. HCl, its suspension dissolves

[B] With conc. aq. NaOH, its suspension dissolves.

[C] With conc. aq. NaOH, its clear solution forms a precipitate.

[D] With conc. aq. HCl, its clear solution forms a precipitate.

[E] With conc. aq. HCl, its suspension dissolves

29. In which aqueous system is PbI2 least soluble?

   [A] 0.5 M HI [B] H2O [C] 1.0 M HNO3 [D] 0.2 M HI [E] 0.8 M KI

30. In which of the following aqueous solutions would you expect AgCl to have the lowest solubility?

[A] pure water [B] 0.010 M KCl [C] 0.020 M LiCl

[D] 0.015 M NaCl [E] 0.0050 M AgNO3

31. A solution of NaF is added dropwise to a solution that is 0.0144 M in Ba2+. When the concentration of F- exceeds ________ M, BaF2 will precipitate. Neglect volume changes. For BaF2, Ksp = 1.7 x 10-6.

   [A] 1.2 x 10-4 [B] 1.1 x 10-2 [C] 5.9 x 10-5 [D] 2.7 x 10-3 [E] 2.4 x 10-8

Explanation / Answer

27. Which one of the following is NOT amphoteric?

amphoteric = can act as either ACID or BASE

Bronsted Lowry acid: any species that will donate H+ (protons) in solution, and makes pH lower (i.e HCl)

Bronsted Lowry base: any species that will accept H+ (protons) in solution, and makes pH higher (NH3 will accept H+ to form NH4+)

[A] Zn(OH)2 this is amphoteics, since Zn(OH)2 can donate Zn+2 + 2OH- and also accept more OH- to form the complex: Zn(OH)2 + 2OH- = Zn(OH)4-2

[B] Sn(OH)2 this is only a base, cant accept more OH- ions

[C] Ca(OH)2  this is only a base, cant accept more OH- ions

D] Cr(OH)3 this is only a base, cant accept more OH- ions

[E] Al(OH)3 this is similar to A, will accept OH- and donate OH- , it forms the complex Al(OH)4-

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