Calculate the mass in grams of a single water molecule.

(a) 5.94 × 1020 H2O2 molecules

(b) 2.8 × 1022 SO2 molecules

(c) 4.5 × 1025 O3 molecules

(d) 9.85 × 1019 CH4 molecules

Solution 54P

Here, we are going to calculate the mass of each of the given samples.

Step 1:

One mole of any species is that quantity in number having a mass equal to its atomic or molecular mass in grams.

The number of particles (atoms, molecules or ions) present in 1 mole of any substance is fixed, with a value of 6.022 × 1023. This is an experimentally obtained value. This number is called the Avogadro Constant or Avogadro Number.

Step 2:

Therefore, 1 mole = molar mass

1 mole = Avogadro number of particles

Combining the two statements, we get,

Mass of Avogadro’s number of particles = Molar mass

Therefore, mass of given number of particles = (Molar mass / Avogadro's number) x given number of particles

Thus,

The mass of given sample = (given number of particles/Avogadro's number) x molar mass