Redox potential of acid mine water; EO for the Fe3+/Fe2+ is 0.77v. I can't wrap my mind around this...

90. What is the redox potential of an acid mine water sample having Fe3+ = 7 x E-03 M and Fe2+ = 5 x E-04 M given that E0 for the Fe3+/Fe2+ couple is 0.77v.

How much Fe++ could be present in water containing 2 x 1e-02 M HCO3- .....

146. How much Fe++ could be present in water containing 2 x 1e-02 M HCO3- (bicarbonate) without causing the precipitation of FeCO3 (Ksp=10**(-10.7))? ***I don't even know where to start.

Steady state conc. of O2 radicals is 0.04 ppmv @ 25 deg C

Please note: this is the second time that this question has been posted. The answer is NOT a. 4.00 x 10 ^-8 atm, b. 1.63 x 10^-9 mol/L, c. =9.86 x 10 ^13 molecules/cm^3 121. During a photochemical smog episode in the coastal city of Seattle, the steady-state concentration of oxygen radicals at ground level was measured to be 0.04 ppmv at 25 degrees celsius. Convert this value to: a. partial pressure in atm b. the molarity scale c. the molecules per cm-3 scale ****Please answer only if you're 100% sure you're right - my program is very picky and likes to tell me that the answer's wrong :( Thanks!!

Combustion temps; Calc. Concentration of nitric oxide in equilibrium with....

NOTE: This is the second time that this question has been posted, so please DO NOT respond unless you are 100% sure about your response. The answer is NOT 3.87 x 10^-9 M. 124. At combustion temperatures, the equilibrium constant for the reaction N2 + O2 -> 2NO is about 5.0E-14. Calculate the concentration of nitric oxide that is in equilibrium with atmospheric levels of nitrogen and oxygen.

A 10.0 mL sample of river water was titrated with 0.0010 M Na2Cr2O7 and required 8.3 mL to reach the end-point...

186) A 10.0 mL sample of river water was titrated with 0.0010 M Na2Cr2O7 and required 8.3 mL to reach the end-point. What is the chemical oxygen demand, in milligrams of O2 per liter, of the sample?