Question

A voltaic cell is constructed using the reaction of chromium metal and iron(II) ion:                                      2Cr_(s) +3Fe²⁺_(aq) ® 2Cr³⁺_(aq) +3Fe_(s)

What is the correct cell notation for this voltaic cell?

Which insoluble compound in each pair should be more soluble in nitric acid than in pure water?

a)    PbCl₂ or PbS

b)    Ag₂CO₃ or AgI

c)    Al(OH)₃ or AgCl

Answer 1

First look at the solubility product values.
.......................Ksp
PbCl2...........1.70 x 10^-5
PbS.............3 x 10^-38

Ksp = [Pb^2+][Cl^-]^2 = (x)(2x)^2 =
4x^3 = 1.70 x 10^-5
x^3 = 4.25 x 10^-6
x = 1.62 x 10^-2 M = [Pb^2+] This is slightly soluble in water.

PbS
Ksp = [Pb^2+][S^2-] = 3 x 10^-38
x^2 = 3 x 10^-38
x = 1.7 x 10^-19 M = [Pb^2+] This is very insoluble in water.

Ion Solubility Exceptions
NO3– ...soluble...... none
ClO4– ..soluble...... none
Cl– .......soluble...... except Ag+, Hg22+, *Pb2+
I– ..........soluble...... except Ag+, Hg22+, *Pb2+
SO42-.. soluble...... except Ca2+, Ba2+, Sr2+, Hg2+, Pb2+, Ag+
CO32-.. insoluble...except Group IA and NH4+
PO43- ..insoluble.. except Group IA and NH4+
OH–...... insoluble.. except Group IA, *Ca2+, Ba2+, Sr2+
S2-........ insoluble.. except Group IA, IIA and NH4+
Na+...... soluble...... none
K+ ....... soluble...... none
NH4+... soluble...... none