Q104P - Chemistry: Molecular Nature Of Matter And Change

Question

Give the number of atoms of the specified element in a formula unit of each of the following compounds, and calculate the molecular(formula) mass:

$$\begin{gathered} \mathbf{\left(}\mathbf{a}\mathbf{\right)}\mathbf{ }\mathbf{Oxygen}\mathbf{ }\mathbf{in}\mathbf{ }\mathbf{aluminium}\mathbf{ }\mathbf{sulfate}\mathbf{,}{\mathbf{AI}}_{\mathbf{2}}{\left({\mathrm{SO}}_4\right)}_{\mathbf{3}} \\ \mathbf{ }\mathbf{\left(}\mathbf{b}\mathbf{\right)}\mathbf{ }\mathbf{Hydrogen}\mathbf{ }\mathbf{in}\mathbf{ }\mathbf{Chloric}\mathbf{ }\mathbf{acid}\mathbf{,}{\left({\mathrm{NH}}_4\right)}_{\mathbf{2}}{\mathbf{HPO}}_{\mathbf{4}} \\ \mathbf{ }\mathbf{ }\mathbf{\left(}\mathbf{c}\mathbf{\right)}\mathbf{ }\mathbf{Oxygen}\mathbf{ }\mathbf{in}\mathbf{ }\mathbf{the}\mathbf{ }\mathbf{mineral}\mathbf{ }\mathbf{azurite}\mathbf{,}{\mathbf{Cu}}_{\mathbf{3}}{\left(\mathrm{OH}\right)}_{\mathbf{2}}{\left({\mathrm{CO}}_3\right)}_{\mathbf{2}} \end{gathered}$$

Step-by-Step Solution

Answer

(a) The Number of atoms is 12 O-toms, and the Molecular mass is 342.17 amu.

(b) The Number of atoms is 9H-atoms, and the Molecular mass is 132.02 amu.

(c) The Number of atoms is 8 O-atoms, and the Molecular mass is 344.67 amu

Step 1:Detail information about aluminium sulfate AI 2 ( SO 4 ) 3

There are 4 oxygen atoms in sulfate ${\mathbf{SO}}_{\mathbf{4}}^{\mathbf{3}\mathbf{-}}$and there are 3 sulfate ions present.

We have $\mathbf{3}\mathbf{\times }\mathbf{4}\mathbf{=}\mathbf{12}\mathbf{ }\mathbf{O}\mathbf{-}\mathbf{atoms}\mathbf{ }\mathbf{atoms}\mathbf{ }\mathbf{in}\mathbf{ }{\mathbf{AI}}_{\mathbf{2}}{\mathbf{\left(}{\mathbf{SO}}_{\mathbf{4}}\mathbf{\right)}}_{\mathbf{3}}$.

List the atomic mass of each of the elements present : 

$\mathbf{AI}\mathbf{=}\mathbf{26}\mathbf{.}\mathbf{98}\mathbf{ }\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{S}\mathbf{=}\mathbf{32}\mathbf{.}\mathbf{07}\mathbf{ }\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{O}\mathbf{=}\mathbf{15}\mathbf{.}\mathbf{99}\mathbf{ }\mathbf{u}$ 

Then add the atomic masses of the constituent atoms to get the molecular formula mass.

Molecular mass $$\begin{gathered} \mathbf{=}\mathbf{2}\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{AI}\mathbf{+}\mathbf{3}\mathbf{(}\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{S}\mathbf{+}\mathbf{4}\mathbf{ }\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{O}\mathbf{)} \\ \mathbf{=}\mathbf{2}\left(26.98\right)\mathbf{+}\mathbf{3}\left(32.07+4\left(15.99\right)\right) \end{gathered}$$

 Molecular mass $\mathbf{=}\mathbf{342}\mathbf{.}\mathbf{17}$amu.

Step 2: Details about caloric acid, ( NH 4 ) 2 HPO 4

There are 4 Hydrogen atoms in ammonium ${\mathbf{NH}}_{\mathbf{4}}^{\mathbf{+}}$and there are 2 ammonium ions present in the given compound.

So there are $\mathbf{2}\mathbf{\times }\mathbf{4}\mathbf{=}\mathbf{8}\mathbf{H}\mathbf{-}\mathbf{atoms}$ in ammonium. And we also have 1 hydrogen atom in hydrogen phosphate.

So, now we have a total of 9 hydrogen atoms ${\left({\mathrm{NH}}_4\right)}_{\mathbf{2}}{\mathbf{HPO}}_{\mathbf{4}}$.

List the atomic mass of each of the elements present.

$\mathbf{N}\mathbf{=}\mathbf{14}\mathbf{.}\mathbf{00}\mathbf{uH}\mathbf{=}\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{uP}\mathbf{=}\mathbf{30}\mathbf{.}\mathbf{97}\mathbf{uO}\mathbf{=}\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{u}$ 

Then add the atomic masses of the constituent atoms.

Molecular mass  

$$\begin{gathered} \mathbf{=}\mathbf{2}\mathbf{\times }\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{N}\mathbf{+}\mathbf{9}\mathbf{ }\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{H}\mathbf{+}\mathbf{4}\mathbf{ }\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{O}\mathbf{+}\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{P} \\ \mathbf{=}\mathbf{2}\mathbf{\times }\mathbf{14}\mathbf{.}\mathbf{00}\mathbf{+}\mathbf{9}\left(1.01\right)\mathbf{+}\mathbf{4}\mathbf{\times }\left(15.99\right)\mathbf{+}\mathbf{30}\mathbf{.}\mathbf{97} \\ \mathrm{Molecular} \mathrm{mass}\mathbf{=}\mathbf{132}\mathbf{.}\mathbf{02}\mathbf{ }\mathrm{amu}. \end{gathered}$$

Step 3: Details of mineral azurite, Cu 3 ( OH ) 2 ( CO 3 ) 2

There is one oxygen in hydroxide and there are two hydroxide ions present in the mineral azurite. 

And there are also3oxygen atoms in each carbonate ion and again there are two carbonate ions.

So, we total oxygen atoms in azurite are, $\left(2\times 1\right)\mathbf{+}\left(2\times 3\right)\mathbf{=}\mathbf{8}\mathbf{ }\mathbf{O}\mathbf{-}\mathbf{atoms}$

List the atomic mass of each of the elements present.

$\mathbf{Cu}\mathbf{=}\mathbf{63}\mathbf{.}\mathbf{55}\mathbf{u}\mathbf{ }\mathbf{O}\mathbf{=}\mathbf{15}\mathbf{.}\mathbf{99}\mathbf{u}\mathbf{ }\mathbf{H}\mathbf{=}\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{u}\mathbf{ }\mathbf{C}\mathbf{=}\mathbf{12}\mathbf{.}\mathbf{01}\mathbf{u}$ 

Then add the atomic masses of the constituent atoms.

$$\begin{gathered} Molecular mass\mathbf{ }\mathbf{=}\mathbf{3}\mathbf{Cu}\mathbf{+}\mathbf{2}\mathbf{(}\mathbf{O}\mathbf{+}\mathbf{H}\mathbf{)}\mathbf{+}\mathbf{2}\mathbf{(}\mathbf{C}\mathbf{+}\mathbf{3}\mathbf{O}\mathbf{)} \\ \mathbf{=}\mathbf{3}\mathbf{(}\mathbf{63}\mathbf{.}\mathbf{55}\mathbf{)}\mathbf{+}\mathbf{2}\mathbf{(}\mathbf{15}\mathbf{.}\mathbf{99}\mathbf{+}\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{)}\mathbf{+}\mathbf{2}\mathbf{(}\mathbf{12}\mathbf{.}\mathbf{01}\mathbf{+}\mathbf{3}\left(16.00\right)\mathbf{)} \end{gathered}$$

 Molecular mass $=344.67 \mathrm{amu}.$