Q113P - Chemistry: Molecular Nature Of Matter And Change

Question

Give the name, empirical formula and molecular mass of the molecule depicted in the figure.

                                     

Step-by-Step Solution

Answer

Molecular Name – Tetraphosphrous hexaoxide

Empirical formula -  

Molecular Mass -  

Step 1: Defining name, empirical formula and molecular mass

Molecular mass is defined as the sum of atomic masses of atoms that are all present in the molecule.

The chemical composition of the substance is given by the molecular formula and the elements present in the simplest whole-number ratio give the empirical formula.

The molecular name gives the composition of chemical elements present in the molecule.

Step 2: Name, molecular formula and molecular mass of the given structure

Four phosphorous atoms are present as central atoms which are linked to six oxygen atoms as terminal atoms. It gives the formula, ${\mathbf{P}}_{\mathbf{4}}{\mathbf{O}}_{\mathbf{6}}$ .

This is a covalent compound, so the name is based on a number of atoms using prefixes.

The second element or the terminal atom changes its ending to “-ide”.

The molecular name is Tetra-phosphorous-hexaoxide.

For the empirical formula, a subscript is divided by the greatest common factor  .

 $$\begin{gathered} {\mathbf{P}}_{\mathbf{4}}{\mathbf{O}}_{\mathbf{6}}\mathbf{=}\mathbf{P}\mathbf{:}\mathbf{O}\mathbf{:}\mathbf{:}\mathbf{4}\mathbf{:}\mathbf{6} \\ \mathbf{or}\mathbf{ }\mathbf{simplest}\mathbf{ }\mathbf{ratio}\mathbf{,}\mathbf{ }\mathbf{P}\mathbf{:}\mathbf{O}\mathbf{:}\mathbf{:}\mathbf{2}\mathbf{:}\mathbf{3} \\ \mathbf{Empiri}\mathbf{ }\mathbf{calformula}\mathbf{ }\mathbf{\to }{\mathbf{P}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}} \end{gathered}$$

The atomic mass of the element,

$\mathbf{P}\mathbf{=}\mathbf{30}\mathbf{.}\mathbf{97}\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{O}\mathbf{=}\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{u}$ 

$$\begin{gathered} \mathbf{Molecular}\mathbf{ }\mathbf{mass}\mathbf{=}\mathbf{4}\mathbf{\times }\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{P}\mathbf{+}\mathbf{6}\mathbf{\times }\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{O} \\ \mathbf{=}\mathbf{4}\mathbf{(}\mathbf{30}\mathbf{.}\mathbf{97}\mathbf{)}\mathbf{+}\mathbf{6}\mathbf{(}\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{)} \end{gathered}$$

Molecular Mass = 219.88 amu