Question

How many atoms of calcium will have the same weight as 20 molecules of SO₃

Answer 1

Calcium

• Calcium is an alkaline earth metal.
• Atomic weight of calcium = 40 u.

${{\mathrm{SO}}_3}^{-2}$

• ${{\mathrm{SO}}_3}^{-2}$ , Sulfur trioxide is a chemical compound consisting of sulfur and 3 oxygen atoms with a charge of -2.
• Mass of ${{\mathrm{SO}}_3}^{-2}$ = Mass of sulfur + (3 x Mass of oxygen)

= 32 + (3 x 16)

= 80 u

• Mass of 20 molecules of sulfur trioxide = 20 x 80

= 1600 u

The number of atoms of calcium having the same weight as 20 sulfur trioxide molecules can be calculated as:

$$\begin{gathered} Numberofatomsofcalciumhavingthesameweightas20sulfurtrioxidemolecules=\frac{massof20moleculesofsulfurtrioxide}{massofonecalciumatom} \\ =\frac{1600}{40} \\ =\mathbf{40}\mathbf{}\mathit{a}\mathit{t}\mathit{o}\mathit{m}\mathit{s} \end{gathered}$$

Hence 40 atoms of calcium have the same weight as 20 molecules of Sulfur trioxide.