# Homework 3: Electrochemistry, Thermodynamics and Coordination Complexes

There are select solutions to these problems here.

### Q3.1

Calculate $$\mathrm{\Delta G^\circ}$$ for the following reactions and determine if it is spontaneous:

1. $$\mathrm{NO_3^-(aq) + Al(s) + 4H^+(aq) \rightarrow NO(g) + Al^{3+}(aq) + 2H_2O (l)}$$
2. $$\mathrm{F_2(g) + 2Li(s) \rightarrow 2F^- (aq) + 2Li^+ (aq)}$$

### S3.1

1. $$\mathrm{NO_3^-(aq) + Al(s) + 4H^+(aq) \rightarrow NO(g) + Al^{3+}(aq) + 2H_2O (l)}$$

$$\mathrm{NO_3^-(aq) + 4H^+(aq) + 3e^- \rightarrow NO(g) + 2H_2O (l)}$$ (reduction) 0.96V

$$\mathrm{Al(s) \rightarrow Al^{3+}(aq) + 3e^-}$$ (oxidation) -1.676V

$$\mathrm{E^\circ}$$ = 0.96 - (-1.676) = 2.636V

$$\mathrm{\Delta G^\circ}$$ = -nF$$\mathrm{E^\circ}$$ = -3(96485)(2.636) = -763.003kJ, negative $$\mathrm{\Delta G^\circ}$$, so spontaneous reaction

b. $$\mathrm{F_2(g) + 2Li(s) \rightarrow 2F^- (aq) + 2Li^+ (aq)}$$

$$\mathrm{F_2(g) + 2e^- \rightarrow 2F^- (aq)}$$ (reduction) 2.87V

$$\mathrm{2Li(s) \rightarrow 2Li^+ +2e^-(aq)}$$ (oxidation) -3.045V

$$\mathrm{E^\circ}$$ = 2.87 - (-3.045) = 5.915V

$$\mathrm{\Delta G^\circ}$$ = -nF$$\mathrm{E^\circ}$$ = -2(96485)(5.915) = -1141.14kJ, negative $$\mathrm{\Delta G^\circ}$$, so spontaneous reaction

### Q3.2

Calculate $$\mathrm{E_{cell}}$$​ using the Nernst equation for the following cells.

1. $$\mathrm{Zn(s) | Zn^{2+}(aq)(0.1\,M) || Sn^{2+}(aq)(.8\,M) | Sn(s)}$$
2. $$\mathrm{Cu(s) | Cu^{+}(aq)(0.4\,M) || F^{-}(aq)(O.9\,M) | F_2(g)(0.5\,atm) | Pt(s)}$$

Need help? Visit the page "Cell Potential".

### S3.2

1. $$\mathrm{Zn(s) | Zn^{2+}(aq)(0.1\,M) || Sn^{2+}(aq)(.8\,M) | Sn(s)}$$

b. $$\mathrm{Cu(s) | Cu^{+}(aq)(0.4\,M) || F^{-}(aq)(O.9\,M) | F_2(g)(0.5\,atm) | Pt(s)}$$

### Q3.3

What’s the pressure of $$\mathrm{NO_2}$$ in the cell diagram

$\mathrm{Pt(s) | NO_2(g) | HNO_2(0.5\:M) || Ag^+(0.7\:M) | Ag(s)}$

given that the $$\href{/Analytical_Chemistry/Electrochemistry/Nernst_Equation#Introduction}{\mathrm{E_{cell}}}$$ is 3.1 V and $$\mathrm{[H^+] = 10^{-6}\, M}$$?

### Q3.4

The cell potential of the following voltaic cell is$$\mathrm{E_{cell}= 1.500\: V}$$. What is $$\ce{[Ag+]}$$ in the cell?

$\mathrm{Zn(s)|Zn^{2+}(1.50\,M)||Ag^+(?\,M)|Ag(s)}$

### Q3.5

Consider the following voltaic cell:

$\mathrm{Ag(s)|Ag^+(saturated\:Ag_2CrO_4)||Ag^+(0.125\,M)|Ag(s)}$

What is $$\mathrm{E_{cell}}$$ if $$\mathrm{K_{sp}=1.2\times10^{-11}}$$ for $$\ce{Ag2CrO4}$$?

### Q3.6

An external wire carrying 2.15 A of current was one for 60 min for each of the the aqueous solutions containing the matal ions below. How much metal (in g) is formed at the cathode?

1. $$\ce{Zn^2+}$$
2. $$\ce{Al^3+}$$
3. $$\ce{Ag+}$$
4. $$\ce{Ni^2+}$$

### Q3.7

How many grams of the given metal are going to be deposited at the cathode by the passage of 2.00 A of current for 60 minutes in electrolysis of aqueous solution with

1. $$\ce{Cu^2+}$$
2. $$\ce{Li+}$$
3. $$\ce{Pb^2+}$$
4. $$\ce{Mg^2+}$$

### Q3.8

What voltage is required for the electrolysis of the following reactions? All reactants are in standards states.

1. $$\mathrm{Zn(s) + Sn^{2+}(aq) \rightarrow Zn^{2+}(aq) + Sn(s)}$$
2. $$\mathrm{2Fe^{2+}(aq) + Hg^{2+}(aq) \rightarrow 2Fe^{3+}(aq) + Hg(l)}$$
3. $$\mathrm{Cu(s) + Sr^{2+}(aq) \rightarrow Cu^{2+}(aq) + Sr(s)}$$

### Q3.9

Consider the following cell

$\mathrm{N_2H_4(aq) + O_2(g) \rightarrow N_2(g) + 2H_2O(l)}$

with $$E^\circ_{cell}=1.559\:V$$

Calculate $$\mathrm{\Delta G^\circ_f}$$ for $$\ce{[N2H4(aq)]}$$.

### Q3.10

Of the following metals potassium, lead, cobalt, and magnesium, which would act as a sacrificial anode for zinc?

### Q3.11

Name the following complex ions or coordination compounds:

1. $$\ce{[Co(OH)2(H2O)4]}$$
2. $$\ce{[Ni(OH)3(CO)3]}$$
3. $$\ce{[Pt(NH3)(CN)3][PtBr6]}$$
4. $$\ce{[Cu(CN)4(en)2]-}$$
5. $$\ce{Au2[SnCl4]}$$

### Q3.12

Draw Lewis Structures for the following ligands:

1. $$\ce{NH3}$$
2. $$\ce{CO}$$
3. $$\ce{CN}$$
4. $$\ce{OH}$$

### Q3.13

Draw out the following structures

1. $$\ce{[PtF4]^2-}$$
2. $$\textrm{fac-}\ce{[Co(H2O)3(NH3)3]^2+}$$
3. $$\ce{[FeSCN(H2O)5]^2+}$$

### Q3.14

Write acceptable names for the following compounds or complex ions:

1. $$\ce{[Cr(H2O)2(CO)2Cl2]}$$
2. $$\ce{[Cr(NH3)3(H2O)3]Cl3}$$
3. $$\ce{[PtCl(H2O)3]+}$$
4. $$\ce{[Al(OH)(H2O)8]Cl2}$$
5. $$\ce{[Co(NH3)4]Br3}$$

### Q3.15

Name the following complex ions or coordination compounds:

1. $$\ce{[Co(OH)2(H2O)4]}$$
2. $$\ce{[Ni(OH)3(CO)3]}$$
3. $$\ce{[Pt(H2O)(NH3)3][PtBr6]}$$
4. $$\ce{[Cu(CN)4(en)2]-}$$
5. $$\ce{Au2[SnCl4]}$$

### Q3.16

Draw Lewis structures for the following ligands:

1. $$\ce{NH3}$$
2. $$\ce{SO4^2-}$$
3. $$\ce{NO}$$
4. $$\ce{H2O}$$

### Q3.17

Draw a plausible structure to represent each of the following:

1. $$\ce{[CrBr4]^2-}$$
2. $$\ce{[AlBr(NH3)5]}$$
3. $$\textrm{fac-}\ce{[PdCl3(NH3)3]-}$$

### Q3.18

Draw the following structures:

1. hexaaquairon(III) ion
2. diamminediaaquacopper(II) ion
3. diamminedichloroplatinum

### Q3.19

Why do tetrahedral and linear structures not display cis and trans isomers?

### Q3.20

If $$\ce{W}$$, $$\ce{X}$$, $$\ce{Y}$$, and $$\ce{Z}$$ were monodentate ligands:

1. List all geometric isomers for $$\ce{[PtWXYZ]^3+}$$.
2. If $$\ce{[PtWXYZ]^3+}$$ were tetrahedral, would there be optical isomers?

### Q3.21

Draw a structure for cis-dibromobis(en)iron(III). Is it optically active? In addition, draw the trans isomer and determine if the ion is chiral.

### Q3.22

Sketch all possible structures of isomers of $$\ce{[CoCl(ox)(NH3)]}$$

### Q3.23

Draw out all of the geometric isomers of $$\ce{[CoCl2(ox)(NH3)2]-}$$

### Q3.24

Of the following complexes, name whether each pair is identical, geometric, or enantiomers (optical isomers).

### Q3M.1

An electric current is passed through an aqueous solution of lithium bromide.

1. What is produced at the cathode?
2. What is produced at the anode?

### Q3M.2

An electric current is passed through an aqueous solution of lead(II) chloride.

1. Write the half-reaction that takes place at the cathode.
2. Write the half-reaction that takes place at the anode.

### Q3M.3

“White gold” it is plated with rhodium (Rh) in order to make it look more like silver. How many coulombs of electricity must be pumped through an rhodium(III) solution in order to plate 1 gram of solid rhodium?

### Q3M.4

A solution of $$MnO_4^{2–}$$ is electrolytically reduced to $$Mn^{3+}$$. A current of 8.64 amp is passed through the solution for 15.0 minutes. What is the number of moles of $$Mn^{3+}$$ produced in this process? (1 faraday = 96,486 coulombs)

S3M.4

8.64 A for 15 minutes -->

8.64 C/s x 15 minutes x 60 s/minute = 7776 Coulombs

1 Faraday = 96,486 Coulombs --->

$$MnO_4^{2–}$$ + 3e- → $$Mn^{3+}$$

For every 3 Faraday consumed, one mole of $$Mn^{3+}$$ is produced.

Therefore:

0.081 Faraday x 1 mole $$Mn^{3+}$$/3 Faraday = 0.027 mol $$Mn^{3+}$$

### Q3M.5

Circle the correct answers: In coordination complexes, the donor atom of a ligand is

1. a Lewis acid.
2. the counter ion
3. the central metal atom.
4. the atom in the ligand that shares an electron pair with the metal.
5. the atom in the ligand that accepts a share in an electron pair from the metal.

### S3M.5

Answer is d. The donor atom of a ligand is the atom that shares an electron pair with the metal.

### Q3M.6

Consider the coordination compound, $$Na_2[Pt(CN)_4]$$. The Lewis acid is

1. $$[Pt(CN)_4]^{2-}$$
2. $$Na^+$$
3. $$Pt$$
4. $$Pt^{2+}$$
5. $$CN^-$$

S3M.6

d. $$Pt^{2+}$$ is the ion that accept the electron pair as the ligand is the Lewis base or electron pair donor.

### Q3M.7

Which one of the following complexes can exhibit geometrical isomerism?

1. $$[Pt(NH_3)_2Cl_2]$$ (square planar)
2. $$[Zn(NH_3)_2Cl_2]$$ (tetrahedral)
3. $$[Cu(NH_3)_4]^{2+}$$ (square planar)
4. $$[Co(NH_3)_5Cl]^{2+}$$ (octahedral)
5. $$[Cu(CN)_2]^-$$ (linear)

### S3M.7

Answer is a. $$[Pt(NH_3)_2Cl_2]$$ (square planar)

### Q3M.8

Determine the number of moles of $$AgBr$$ which will be formed by reaction of one mole of the following compounds with an excess of $$AgNO_{3 \, (aq)}$$.

1. $$[CoBr(NH_3)_5]Br_2$$
2. $$[Co(en)_3]Br_3$$
3. $$[CoBr_2(NH_3)_5]Br$$

### Q3M.9

Determine the coordination number and oxidation number of the central metal atom in each of the following: compounds:

1. $$[CrBr_2(NH_3)_4]Br$$
2. $$K_4[Co(C_2O_4)_3]$$
3. $$[Al(OH)(H_2O)_5]SO_4$$
4. $$[Cu(CN)_4]_2$$

### S3M.9

a) Coordination number: 6
Oxidation number: +3

b) Coordination number: 6
Oxidation number: +2

c) Coordination number: 6
Oxidation number: +3

d) Coordination number: 4
Oxidation number: +2

### Q3M.10

For the following four complexes or compounds, indicate the missing properties. The first row was done for you as an example.

Full name Molecular Formula Proposed Structure* Coordination Number Oxidation State of central atom # of d-electrons of central atom
Tetraamminecopper(II) $$[Cu(NH_3)_4]^{2+}$$ 4 2 9
TetraChloro(nickel(0))
$$[NiCl_4]Cl_2$$ mer-triaquatriamminechromium(III) chloride

* I am willing to accept plausible geometries that may not be the actual one experimental observed.