Question

What is the mass of:
(a) 0.2 mole of oxygen atoms
(b) 0.5 mole of a water molecule

Answer 1

Hint:
A mole is defined as the unit of any substance which is equivalent to \[\text{6}\text{.022 }\cdot \text{ 1}{{\text{0}}^{23}}\] particles and the particles can be any atom, elements, etc. The SI unit of a mole is 'mol'. Atoms are the smallest particles which bond with each other to form a molecule.

Complete step by step answer:
-To calculate the mass of 0.2 moles of oxygen atom we should know the mass of a single atom of oxygen that is 16.
-So, as we know that one mole of oxygen has a mass of 16 gram then the mass of 0.2 moles will be:
\[\text{0}\text{.2 }\cdot \text{ 16 = 3}\text{.2 gram}\]
-Similarly, to calculate the mass of 0.5 moles of a water molecule, we have to find the molecular mass of 1 mol of water that is:
$\text{Mass = 2 +16 = 18}$
-So, as the mass of 1 mol of water is 18 then the mass of 0.5 moles of water will be:
\[\text{18 }\cdot \text{ 0}\text{.5 = 9}\text{.0 gram}\]
-Therefore, the mass of 0.2 moles of oxygen atom is 3.2 grams and the mass of 0.5 moles of a water molecule is 9.0 grams.

Note:
If one wants to calculate the number of moles of any substance then they should use the formula that is equal to the ratio of the mass and molecular mass. Moreover, the number of moles is directly proportional to the number of molecules as well as to the volume of a substance.