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Question 1

Complex Ion Formation

Answer 1

• A complex ion is an ion containing a central metal cation bonded to one or more molecules or ions
• A solution of CoCl2 is pink because of the presence of Co(H2O)6 2+ ions.
• When HCl is added to a CoCL2 solution, there is a color change from pink to blue.
• This solution is blue because of the presence of CoCl4 2- ions.
  CO2+ (aq) + 4Cl- (aq) <> CoCl4 2- (aq)
  Cu2+ (aq) + 2OH- (aq) > Cu(OH)2 (s)
  Cu(OH)2 (s) + 4NH3 (aq) <> Cu(NH3)4 2+ (aq) + 2OH- (aq)
  The formation of the Cu(NH3)4 2+ ion can be expressed as
  Cu2+ (aq) + 4NH3 (aq) <> Cu(NH3)4 2+ (aq)
  Kf = [Cu(NH3)4 2+] / ([Cu2+][NH3]^4)

Question 2

Separation of Ions Using Differences in Solubility

Answer 2

• Some compounds can be separated based on fractional precipitation.
• “Fractional precipitation” is the separation of mixture based upon the components’ solubilities
  Compound / Ksp
  AgCl / 1.610^-10
  AgBr / 7.710^-13
  AgI / 8.3*10^-17

Question 3

Example: Silver nitrate is added slowly to a solution that is 0.020M in Cl- ions and 0.020M in Br ions. Calculate the concentration of Ag+ ions (in mol/L) required to initiate the precipitation of AgBr without precipitating AgCl.

Answer 3

• AgCl (s) <> Ag+ (aq) + Cl- (aq)
  Ksp = 1.6*10^-10 = [Ag+][Cl-]
• AgBr (s) <> Ag+ (aq) + Br- (aq)
  Ksp = 7.7*10^-13 = [Ag+][Br-]
• [Ag+] = Ksp / [Br-] = 7.710^-13 / 0.020 = 3.910^-11M
• [Ag+] = Ksp / [Cl-] = 1.610^-10 / 0.020 = 8.010^-9M
• [Br-] = Ksp / [Ag+] = 7.710^-13 / 8.010^-9 = 9.6*10^-5M
• AgCl (s) <> Ag+ (aq) + Cl-(aq); Ksp = 1.77*10^-10
• Ammonia: Ag+ (aq) + 2NH3 (aq) <> Ag(NH3)2+ (aq) = Kf 1.7*10^7
  = AgCl(s) + 2NH3 (aq) <> Ag(NH3)2+ (aq)
• So: k = Ksp Kf = 3.010^-3

Question 4

Entropy and Free Energy

Answer 4

Entropy = distribution of heat spread
- Energy @gas
> Temperature (kinetic molecular theory)
> Increase temperature > increase KE (lower # mol)
- Matter
1. Stoichiometric: 2H2O (l) > 2H2 (g) + O2 (g)
> Compare # moles: this case: Increase to left side
2. Phase change: Solid > liquid > gas
3. Increase volume > entropy

Question 5

Heat death

Answer 5

• Object transferred from hot to cold