Question

What is the molecular mass of a substance, each molecule of which contains 9 carbon atoms, 13 hydrogen atoms and $2.33\times {10}^{-23}$ g of another component?

• A. 135.04
• B. 100
• C. 111
• D. 28

Answer 1

The correct option is A 135.04

The molecule has C, H and other component.
Atomic mass of 1 C atom = 12 amu
Mass of 9 C atoms = $12\times 9=108$ amu
Atomic mass of 1 H atom = 1 amu
Mass of 13 H atoms = $13\times 1=13$ amu
We know, Avagadro number = $6.022\times {10}^{23}$
Mass of other component = $(2.33\times {10}^{-23})\times 6.022\times {10}^{23}$ = 14 amu
$\therefore$ Total mass of one molecule = $108+13+14=135$ amu
$\therefore$ Molecular mass of the substance = 135