Team Lithium Exam 2 Jeopardy

Complex Ions/Solubility

100

Hydroxyapatite is one of the calcium minerals that is an essential component of our teeth. What is the expression for the solubility product of Hydroxyapatite (Ca₁₀(PO₄)₆(OH)_2(s)).

What is K_sp= [Ca²⁺]¹⁰[PO₄³⁻]⁶[OH⁻]² ?

200

If solid PbI₂ is dissolved into 1 part lead ions and 2 parts iodine ions, both of which are aqueous, what would the equation be to solve for the solubility product, in terms of the concentrations of Iodine and Lead.

What is K_sp = [Pb²⁺][I⁺]²?

The concentration of the solid PbI₂ is omitted due to the fact that there is no concentration because it is a solid, lol.

300

What is the effect on the amount of solid Mg(OH)₂ and the concentrations of Mg²⁺ and OH^- when KOH is added to a saturated solution of Mg(OH)₂?

What is increase undissolved magnesium hydroxide?

Adding a common ion, OH- will increase the concentration of this ion and shift the solubility equilibrium to the left, which decreases the concentration of magnesium ions and increases the amount of undissolved magnesium hydroxide. (Common Ion effect)

400

For the complex ion Fe(H₂O)₆²⁺ the acid ionization constant at 298 K is 7.7E-3. What is the pH of a 50 mL solution that contains 0.02 mol of Fe(NO₃)₂?

What is 1.286

500

What is the solubility of CoCO₃ in a 0.2 M solution of Ca(SCN)₂ given Ksp of CoCO₃ = 1.4*10^-13 and Kf of Ca[Co(SCN)₄] = 1.0*10³? Hint: Assume s is negligible.

What is s = 4.7x10^-7?

CoCO3 ⇌ Co2+ + CO32+ Ksp = 1.4*10-13

Co2++4SCN- ⇌ Ca[Co(SCN)4] Kf = 1.0*103

Koverall = Ksp * Kf = 1.4*10-13 * 1.0*103 = 1.4*10-10 

Overall reaction: CoCO3 + 4SCN- ⇌ CO32+ + Ca[Co(SCN)4] 

Ice chart yields K = 1.4*10-10 = (s2)/(0.2-4s)4

Assume s is negligible

Multiply 1.4*10-10 by 0.24

Take square root

s = 4.73*10-7

Precipitation Equilibria

100

What precipitate is formed when aqueous solutions of MgSO₄ and NaOH are mixed?

What is MgOH?

200

NaCl _(aq) + AgNO_{3 aq} -> AgCl _s + NaNO₃

If the above reaction, at room temperature, results in a large amount of solid substance and increasing the temperature results in a dissolving of the solid, would the reaction be considered exothermic or endothermic?

What is exothermic?

Exothermic, as heat is a reactant, and would therefore shift the reaction towards the aqueous components, rather than the solid product.

300

Based on general solubility rules, which of the following compounds is considered soluble?

Cs₂CrO₄

PbCl₂

Al(OH)₃

CaSO₄

What is Cs₂CrO₄ ?

400

Predict whether precipitation will occur when 0.10 M Ca(NO₃)₂ is mixed with 0.01 M NH₄F. Potentially helpful information: Ksp­ of CaF₂ = 4.0 x 10-11

What is proceed in reverse?

CaF­_2(s) ⇌ Ca²⁺_(aq) + 2F^- _(aq)

Q_sp = [Ca²⁺]_init [F^-]_init²

= 0.10 * 0.012 = 1.0 x 10-5

Q > K ⇒ Reaction will proceed in reverse, precipitation will occur.

500

Nigel works at a water treatment plant and has 3 chemicals at his disposal: iron (III) chloride (FeCl₃), Sodium Chloride (NaCl), and Phosphoric Acid (H₃PO₄). Suppose that he is given a solution containing phosphates (PO₄³⁻) and is told that he must add one of the 3 chemicals in order to remove the phosphates out of the solution in the form of a precipitate. Which is the chemical he should use and what is the minimum amount (in grams) needed to completely precipitate 100mL of a 0.5M solution containing phosphates. 

Potentially useful information: 

Molecular weights: FeCl₃ (162.2 g/mol), NaCl (58.44 g/mol), H₃PO₄ (97.99)

What is iron (III) chloride?

He should use iron (III) chloride, as it is the only cation that will form a relatively insoluble product with the Phosphate ion. He should add a minimum of 8.11 grams of iron (III) chloride. 

Work: 

Fe3+ + PO43-  —> FePO4 (s)

(0.1 L) x (0.5 mol/L) = 0.05 moles PO43-

1 mole Fe3+ : 1 mole PO43-

(0.05 moles Fe)x(1 mole FeCl₃/mole Fe₃⁺)x(162.2 g/mol FeCl₃) = 8.11 g FeCl₃

Atmospheric Chemistry

100

What type of atom in the CFC molecule is the most destructive to the ozone layer?

What is chlorine?

200

In the United States, what is the greatest human source of sulfur oxides?

What is electric power companies?

300

Why does a symmetric stretch vibration on a carbon dioxide molecule not result in infrared absorption?

What is no change in dipole moment?

400

What four equilibria contribute to normal acidity in natural bodies of water? (Normal meaning not having to deal with NO_x or SO₂)

What is the dissolution of CO₂, the hydrolysis of CO₂, the first acid ionization of CO₂, and the 2nd acid ionization of CO₂

OR

C0_2(g)~C0_2(aq)

C0_2(ag) + H₂0_(l) ~ H₂C0_3(aq)

H₂C0_3(aq) + H₂0_(l) ~ HC0₃-_(aq) + H₃0⁺ _(aq)

HCO₃^-_(aq) + H₂0_(l) ~ CO₃ 2- _(aq) + H₃0⁺ _(aq)

500

Given the total mass of an alien planet's atmosphere is 6.02214*10²³kg and that the average molecular weight of the air in the atmosphere is 42.00 g/mol , calculate the total mass of oxygen gas in the atmosphere assuming a mixing ratio of 314.15 ppmv for oxygen gas.Give the answer in kg to 4 sig figs.

What is 1.441*10²⁰ kg ?

m_gas/m_air = (mixing ratio)*(M_gasM_air) = 314.15 ppmv*(32.00g/mol / 42.00g/mol) = 239.4ppm

mO2=(6.02214×10²³ kg)(239.4*10-6) =1.441*10²⁰ kg

Answer: 1.441*10²⁰ kg

Lewis Acid/Base

100

Which of the following is not a Lewis Acid?

1. BF₃

2. H⁺

3. SiF₄

4. NH₃

5. SO₂

What is NH₃?

200

In the reaction OH^- + CO₂ → HCO₃, identify the specific atoms in the reactants that act as the lewis acid and lewis base.

Oxygen on OH^- acts as the lewis base, C on CO₂ acts as the lewis acid

300

Chromium (III) ion and ammonia react to produce the complex ion [Cr(NH3)6]3+ . Identify the Lewis Acid and the Lewis Base in this reaction.

What is Cr³⁺ is the lewis acid and NH₃ is the lewis base?

Cr³⁺ is the lewis acid because it accepts the electron pair. NH₃ is the lewis base because it donates the lone pair of electrons on the Nitrogen atom.

400

In this Lewis Acid Base reaction, what species is the lewis acid and what species is the lewis base? 

Al₃+ + 6H₂O ⇌ [Al(H₂O)₆]³⁺

What is aluminum ion is the lewis acid because it is donates electrons and is water is the lewis base because it is electron acceptor?

500

Describe the two coupled equilibria that directly cause CO2-related ocean acidification.

What is H₂CO_{3 (aq)} + H₂O_(l) ⇌ HCO₃^-_(aq) + H₃O⁺_(aq)

HCO₃^-_(aq) + H₂O_(l) ⇌ CO₃^2-_(aq) + H₃O⁺_(aq)

Electro-chemistry

100

Based on the following cell schematic, calculate the standard cell potential for the cell reaction. Is the reaction spontaneous under standard state conditions? 

Cu (s) | Cu²⁺ (aq) || Au³⁺ (aq) | Au (s)

Useful information:

Au³⁺ (aq)  + 3e⁻ —> Au (s)         E⁰ (V) = +1.498

Cu²⁺ (aq)+ 2e⁻ —> Cu (s)        E⁰ (V) = +0.34

What is +1.16 V and the reaction is spontaneous?

Reaction: 3Cu (s) + 2Au³⁺ (aq) —> 3Cu²⁺ (aq) + 2Au (s)

anode-half reaction: Cu²⁺ (aq)+ 2e⁻ —> Cu (s)

cathode-half reaction: Au³⁺ (aq)  + 3e⁻ —> Au (s)

E⁰ cell = E⁰ cathode - E⁰ anode

(1.498) - (0.34) = 1.158… with sig figs = 1.16

200

 What is the change in the oxidation state of Mg in in the reaction CuSO_4(aq)+Mg_(s)--> Cu_(s)+MgSO_4(aq)?

What is 0 to -2?

Mg initially has an oxidation state of 0 and in MgSO₄ each oxygen has an oxidation state of -2. The sulfur has an oxidation state of 6 and the net charge on the compound is zero so Mg has a final oxidation state of 2+ and the change in oxidation state is 2.

300

Which of the following voltaic cells are spontaneous with Zinc at the cathode?

1. Mg(s) | Mg2+(aq) || Zn2+(aq) | Zn(s)

2. Cd(s) | Cd2+(aq) || Zn2+(aq) | Zn(s)

3. Pb(s) | Pb2+(aq) || Zn2+(aq) | Zn(s)

4. Ni(s) | Ni2+(aq) || Zn2+(aq) | Zn(s)

5. Cu(s) | Cu2+(aq) || Zn2+(aq) | Zn(s)

What is Mg(s) | Mg2+(aq) || Zn2+(aq) | Zn(s) ?

400

Determine if the cell reaction in the following concentration cell is spontaneous by determining its cell potential. Assume standard conditions (T = 298.15 K).

Faraday’s constant = 96485.33212 C/mol

Fe (s) | Fe(OH2)62+ (aq) (0.01 M) || Fe(OH2)62+ (aq) (0.10 M) | Fe (s)

What is -4.44 x 105 V and nonspontaneous?

Answer:

Ecell = E∘cell  -  (RT/nF) * ln Q

E∘cell = 0, both electrodes are the same

Ecell = 0 – (8.3145 J/(mol*K) * 298.15 K)/(2 * 96485.33212 C/mol) * ln (0.01/0.10)

Ecell = -4.44 x 105 V, nonspontaneous

500

Calculate the cell potential in V, equilibrium constant, and free energy in kJ of the following reaction (assume room temperature):

AgCl(s) ⇌ Ag+ (aq)+Cl− (aq)

Helpful information:

Ag+(aq) + e− ⟶ Ag(s)                        E° = +0.7996 V

AgCl(s) + e− ⟶ Ag(s) + Cl− (aq)       E° = +0.22233 V

Faraday’s constant = 96485.33212 C/mol

 What is Ecell=-0.5773, K=1.746x10^-10, and ΔG° = -55.6981 kj/mol?

 AgCl(s) + e− ⟶ Ag(s) + Cl− (aq)                reduction

+ Ag(s) ⟶ Ag+(aq) + e−                                                       oxidation

= AgCl(s) ⇌ Ag+ (aq)+Cl− (aq)                    overall

E°cell = E°reduction - E°oxidation = .22233 – 0.7996 = -0.5773

 

E°cell = (RT/nF) * ln K

-0.5773 = (8.3145 J/(mol*K) * 298.15 K)/(1 * 96485.33212 C/mol) * ln K

K = 1.746 x 10-10

ΔG° = - RT ln K = (8.3145 J/(mol*K) * 298.15 K) * ln (1.746 x 10-10)

= -5.56981 x 10-4 J/mol =  -55.6981 kJ/mol