Question

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

Answer 1

Step 1: Molecular weight of Oxygen

• Oxygen is an element present in the 16th group of the periodic table
• It is a colourless, odourless, tasteless gas.
• The molecular weight of oxygen(O₂) = 16 u.

${\mathrm{SO}}_3$(Sulphur trioxide)

• ${\mathrm{SO}}_3$ , Sulphur trioxide is a chemical compound consisting of sulphur and 3 oxygen atoms.
• Mass of ${\mathrm{SO}}_3$ = Mass of sulphur + (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 molecules of oxygen having the same weight as 20 sulfur trioxide molecules can be calculated as:

$$\begin{gathered} \mathrm{Given}, \\ \mathrm{Mass}\mathrm{of}\mathrm{one}\mathrm{molecule}\mathrm{of}\mathrm{oxygen}\times \mathrm{number}\mathrm{of}\mathrm{molecules}\mathrm{of}\mathrm{oxygen}=\mathrm{mass}\mathrm{of}20\mathrm{molecule}\mathrm{of}{\mathrm{SO}}_3 \\ \mathrm{Number}\mathrm{of}\mathrm{molecules}\mathrm{of}\mathrm{oxygen}=\frac{1600\mathrm{u}}{32\mathrm{u}}=50 \end{gathered}$$

Hence 50 molecules of oxygen have the same weight as 20 molecules of Sulfur trioxide.