Question

For which compound does $ 0.256 $ mole weigh $ 12.8g $ ?
(A) $ {C_2}{H_4}O $
(B) $ C{O_2} $
(C) $ C{H_3}Cl $
(D) $ {C_2}{H_6} $

Answer 1

Hint: The number of moles of any compound can be defined as the ratio of the mass of the compound to the molar mass of that compound. Given that a compound does $ 0.256 $ mole and the mass is $ 12.8g $ . By substituting these two values in the below formula gives the molar mass, based on the molar mass compound can be determined.
 $ n = \dfrac{m}{M} $
 $ n $ is the number of moles of a given compound
 $ m $ is the mass of a given compound
 $ M $ is the molar mass of a given compound.

Complete answer:
Given that the compound has a mass of $ 12.8g $ and has the weight of $ 0.256 $ mole.
The number of moles of any compound can be written as the ratio of the mass to the molar mass of the compound.
Substitute these two values in the above formula.
 $ 0.256 = \dfrac{{12.8}}{M} $
By simplification, the value of molar mass will be $ 50gmo{l^{ - 1}} $
Carbon is an element with atomic number $ 6 $ and has molar mass of $ 12gmo{l^{ - 1}} $
Hydrogen is an element with atomic number $ 1 $ and has molar mass of $ 1gmo{l^{ - 1}} $
Oxygen is an element with atomic number $ 8 $ and has molar mass of $ 16gmo{l^{ - 1}} $
Out of the given options,
 $ C{H_3}Cl $ has the molar mass of $ 1\left( {12} \right) + 3\left( 1 \right) + 35.5 = 50.5gmo{l^{ - 1}} $
It is nearly equal to $ 50gmo{l^{ - 1}} $ . Thus, the compound is $ C{H_3}Cl $ .

Note:
Chlorine has the molar mass of $ 35.5gmo{l^{ - 1}} $ . in the compound, $ C{H_3}Cl $ the obtained molar mass is $ 50.5gmo{l^{ - 1}} $ , but the molar mass obtained from the given moles and weight is $ 50gmo{l^{ - 1}} $ . Based on the periodic table only, molar mass of atoms must be considered.