If you have 2.86 gallons of pure water, how many molecules of water are ionized at any given time ?

The molar mass of water is 18 grams per mole. So in 18 grams of water, there are 6.02 x 1023 molecules.

One gallon of water is equal to 3.7854118 liters. If we assume that the water is at 4 °C (to keep things simple), the density of water is exactly 1 gram per milliliter, or 1 kilogram per liter. So 1 gallon of water at 4 °C weighs exactly 3.7854118 kilograms, or 3785.41118 grams.

If one mole of water weighs 18 grams, then there are 210.30 moles of water in a gallon. Since one mole of water is made up of 6.02 x 1023 molecules, in one gallon of water there are 1.266 x 1026 molecules.

That is: 126600000000000000000000000 molecules!

If we multiply that by the number of atoms in a single water molecule -- 3 atoms -- then we get:

379800000000000000000000000 atoms!

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.