Question

Calculate the molecular masses of the following compounds :
(A) Methane, $C{H_4}$
(B) Ethane, ${C_2}{H_6}$
(C) Ethene, ${C_2}{H_4}$
(D) Ethyne, ${C_2}{H_2}$
(Atomic masses : C = 12u, H = 1u).

Answer 1

The molecular mass is the mass of a given molecule. It is measured in Daltons (Da or u). To calculate the molecular mass of a given molecule, take the sum of atomic masses of all the atoms of each element in that molecule.

Complete step by step solution:
-Methane is an alkane having one carbon and four hydrogen atoms bonded. It is the simplest alkane, and it is a major constituent of natural gas. The abundance of methane on earth makes it an attractive fuel. Methane is a tetrahedral molecule with four equivalent carbon-hydrogen bonds. The bonding results in overlapping of valence orbitals on carbon and hydrogen. At room temperature and standard pressure, methane is colourless and odourless gas. Methane is a flammable gas.
Molecular mass of methane = mass of carbon + mass of four atoms of hydrogen
That is,
$12 + 4 = 16{\text{ }}u$
-Ethane is an organic chemical compound having two carbons and six hydrogens. At standard temperature and standard pressure ethane is colourless, odourless and it is in gaseous state. Ethane is isolated from natural gas and petrochemical from by-products of petroleum refining. Molecular mass of ethane = mass of two carbon atoms + mass of six hydrogen atoms
That is,
$12 + 12 + 6 = 30{\text{ }}u$
-Ethene or ethylene is a hydrocarbon having one carbon - carbon double bond. Ethylene is colourless, flammable gas with a faint sweet and musky odour. It is the simplest alkene.
Molecular mass of ethylene = mass of two carbon atoms + mass of 4 hydrogen atoms
That is,
$12 + 12 + 4{\text{ }} = 28u$
-Ethyne also known as acetylene is an organic chemical compound. It has a carbon-carbon triple bond. It is the simplest alkyne. It is a colourless gas and used as a fuel. It is unstable in its pure form.
Molecular mass of ethylene = mass of two carbon atoms + mass of two hydrogen atom
That is,
$12 + 12 + 2 = 26{\text{ }}u$

Note:
-Different molecules of the same compound may have different molecular masses because they might contain various isotopes of the elements.
-Total molecular mass of a compound contains 1 mole of compound.