ENCE 433 Dr. Alba Torrents

ENCE 433 Dr. Alba Torrents

EXAMINATION 3 "SHOW ALL WORK" Fall 1996

Thursday, November 21

No Partial credit for YES/NO; HIGH/LOW without explanation.

State assumption; remember to check them

Clearly indicate intermediate and final results

1. (30) Complete the following table to show how the specified property would vary upon the addition of small amount of the chemical specified in column "2"

indicates the term increases.

--- indicates the term remains the same.

¯ indicates the term decreases.

System	Add	How would vary ?
CaCO₃(s) + H₂O closed	H₂O	[Ca⁺²] C_T
CaCO₃(s) + H₂O open	H₂O	[Ca⁺²] C_T
CaCO₃(s) + H₂O closed	NaHCO₃	[Ca⁺²] C_T
Fe(OH)₂(s) + H₂O	NaOH	Fe⁺² pH
Ag⁺, Cl^- , H₂O IAP = K_so	AgCl(s)	Ag⁺
Ag⁺, Cl^- , H₂O IAP = K_so	H₂O	Ag⁺
Ag⁺, Cl^- , H₂O AgCl(s)	H₂O	Ag⁺

2. (15) The solubility product, Ks_o, for calcium sulfate (CaSO₄) at 25 oC is 1.96x10-4. Determine the Ca+2 concentration for the saturated solution.(assume both H₂SO₄ and HSO₄^- are strong acids).

3.(15) If we mix 70.0 mL of 0.050 F Ba(NO3)2 (a strong electrolyte that completely dissociates) with 30.0 mL of 0.020 F NaF, will any BaF2 precipitate? Kso of BaF2 is 1.7x10-6 at 20oC.

4. (40) Consider a solution of pure water to which an excess of Mn(OH)_{2 (s)} has been added (i.e., the solution is saturated).

(10)What is the solution pH

(10)A gas is bubbled through this solution at a constant (and controllable) partial pressure of CO_{2 (g)}. What would you expect to happen ?

(10) What P_CO2 must be maintained to achieve co-existence of Mn(OH)_{2 (s)} and MnCO_3(s)?

d. (10) If the system is equilibrated with the atmosphere (P_CO2 = 10^-3.5) and has a pH of 7. Which solid phase controls the solubility? What is the concentration of [Mn⁺²] ?