Question

If 3.00 moles of `H_2O` are produced, how many grams of hydrogen gas are used?

Answer 1

If the equation is
`H^+` + `O^-2` `=>` `H_2O`

and if you balance it,
`4H^+` + `2O^-2` `=>` `2H_2O`

Assume that:
n = number of moles
m = mass of substance
M = molar mass (equivalent to atomic weight on the periodic table)

`n = m -: M`

The mole ratio between `H : H_2O` is `4:2`. If you simplify the mole ratio into simplest form, it becomes `2:1`

So, if 1 mole of `H_2O` gives you 2 moles of `H^+`,

then 3.00 moles of `H_2O` must give you:
`[3.00 mol xx 2]` = 6.00 moles of `H^+`

You now know that Hydrogen gas has 6.00 moles. (n)

Your next step is to find the molar mass (M) of hydrogen (`H^+`). If you look into your periodic table, the molar mass of (`H^+`) is 1.00 g/mol.

Since you have found your number of moles (n) and molar mass (M) for hydrogen, your final step is to determine the mass (m).

Looking back at the `n = m-: M` formula, to find mass of substance (m), you need to flip it and it becomes `m = M xx n`

The mass of hydrogen gas is:
m = 1.00 g/mol `xx` 6.00 moles = 6.00 grams of `H^+` gas.

Therefore 6.00 grams of hydrogen gas is being used.