To calculate the pH of a solution that has a [H3O+] of 7.22x10^-7. You would do the following
pH=-log[H3O+]
pH=-log[7.22x10^-7]
pH=?
The pressure of the gas : 1.1685 atm
<h3>Further explanation</h3>
In general, the gas equation can be written

where
P = pressure, atm
V = volume, liter
n = number of moles
R = gas constant = 0.08206 L.atm / mol K
T = temperature, Kelvin
n=moles=1.5
V=volumes = 30 L
T=temperature=285 K
The pressure :

To answer the question above, we take note first that every mole of PCl₃ contains 3 atoms of Cl. First, we divide the given number by 3.
3.68 x 10²⁵ / 3 = 1.227 x 10²⁵
Then, we divide the answer by the Avogadro's number which is equal to 6.022 x 10²³. That is,
1.227 x 10²⁵ / (6.022 x 10²³) = 20.37
Thus, there are 20.37 mol of PCl₃.