Answer to Question #257198 in Inorganic Chemistry for Tahir

Question

1. Assuming that the partial pressure of oxygen in water is that of atmospheric 0₂. 0.21 atm, rather than the 1.00 atm assumed in deriving Equation 4.9.5, derive an equation describing the oxidizing PE limit of water as a function of pH.
2. Plot log PO₂ as a function of PE at pH 7.00.
3. Calculate the pressure of oxygen for a system in equilibrium in which [NH₄⁺) = (NO₃^-) at pH 7.00.

Answer 1

1. In order to be able to calculate the partial pressure of oxygen gas, you need to figure out the mole fraction of oxygen gas in the sample. The mole fraction of oxygen gas is calculated by dividing the number of moles of oxygen gas by the total number of moles of gas present in the sample

moles of oxygen gas

total moles of gas

As you know, Avogadro's constant allows you to convert the number of molecules to moles.

Avogadro's constant

1 mole gas=

$6.022×10^23$ molecules

So, let's assume that this sample contains N

 molecules of gas. Since 21

 of these molecules are molecules of oxygen gas, you can say that this sample contains

=$21/100$

molecules of Oxygen

This means that the number of moles of oxygen gas present in the sample is equal to

mole $= N ÷6.022×10^23 PE = 0.21atm 1/8 NO3- + 5/4 H+ + e- ¬® 1/8NH4+ + 3/8H2O @25°C pE = 14.15$