Question

How many oxygen ATOMS are present in a `75*g` mass of water?

Answer 1

Approx. `70*g` oxygen.

Explanation:

There are `(75*g)/(18.0*g*mol^-1)` `=` `4.17" moles of water"`.

Clearly, if this is the molar quantity of water, it is also the molar quantity of oxygen. Why? Because there is 1 mol of oxygen ATOMS in 1 mol of water. Here I speak of atomic, not molecular, quantities.

So, we simply have to mulitply this molar quantity by the mass of atomic oxygen: `4.17*mol xx15.999*g*mol^-1` `~= 70*g" oxygen"`