Q106P - Chemistry: Molecular Nature Of Matter And Change

Question

Write the formula of each compound, and determine its molecular(formula) mass:

(a) Ammonium Sulfate;

(b) Sodium dihydrogen phosphate;

(c) Potassium bicarbonate.

Step-by-Step Solution

Answer

(a) the formula of the ammonium sulfate is ${\left({\mathrm{NH}}_4\right)}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$and molecular mass is 132.15 amu.

(b) the formula of the Sodium dihydrogen phosphate is ${\mathbf{NaH}}_{\mathbf{2}}{\mathbf{PO}}_{\mathbf{4}}$and Molecular mass is 119.98 amu.

(C) The Formula of the Ammonium Sulfate ${\mathbf{KHCO}}_{\mathbf{3}}$ and molecular mass is 100.12 amu

Step 1: To Write the formula and calculate the molecular mass for Ammonium Sulfate

Ammonium is a polyatomic cation with the formula ${\mathbf{NH}}_{\mathbf{4}}^{\mathbf{+}}$ and sulfate is a polyatomic anion with the formula ${\mathbf{SO}}_{\mathbf{4}}^{\mathbf{2}\mathbf{-}}$

The charges of each ion will just interchange as subscripts to give its molecular formula.

${\mathbf{NH}}_{\mathbf{4}}^{\mathbf{+}}{\mathbf{SO}}_{\mathbf{4}}^{\mathbf{2}\mathbf{-}}\mathbf{\to }{\left({\mathrm{NH}}_4\right)}_{\mathbf{2}}\mathbf{ }{\mathbf{SO}}_{\mathbf{4}}$

List the atomic mass of each of the elements present.

$\mathbf{N}\mathbf{=}\mathbf{14}\mathbf{.}\mathbf{00}\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{H}\mathbf{=}\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{S}\mathbf{=}\mathbf{32}\mathbf{.}\mathbf{07}\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{O}\mathbf{=}\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{u}$

Then add the atomic masses of the constituent atoms.

Molecular mass

$$\begin{gathered} \mathbf{=}\mathbf{2}\mathbf{\times }\mathbf{ }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{N}\mathbf{+}\mathbf{8}\mathbf{\times }\mathbf{ }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{h}\mathbf{+}\mathbf{ }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{S}\mathbf{+}\mathbf{4}\mathbf{\times }\mathbf{ }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{O} \\ \mathbf{=}\mathbf{2}\mathbf{\times }\mathbf{14}\mathbf{.}\mathbf{00}\mathbf{+}\mathbf{8}\mathbf{\times }\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{+}\mathbf{32}\mathbf{.}\mathbf{07}\mathbf{+}\mathbf{4}\mathbf{\times }\mathbf{16}\mathbf{.}\mathbf{000} \end{gathered}$$

Molecular mass  $\mathbf{132}\mathbf{.}\mathbf{15}\mathbf{ }\mathbf{amu}\mathbf{ }\mathrm{amu}.$

Step 2: To Write the formula and calculate the molecular mass for Sodium dihydrogen phosphate

Sodium is a group 1 element with a charge of +1.

Dihydrogen phosphate is a polyatomic anion with the formula ${\mathrm{H}}_2{\mathrm{PO}}_4^{-}$ The Charges of each ion will just interchange as subscripts of its molecular formula.

${\mathbf{Na}}^{\mathbf{+}}{\mathbf{H}}_{\mathbf{2}}{\mathbf{PO}}_{\mathbf{4}}^{\mathbf{-}}\mathbf{\to }{\mathbf{NaH}}_{\mathbf{2}}{\mathbf{PO}}_{\mathbf{4}}$

List the atomic mass of each of the elements present.

$\mathbf{Na}\mathbf{=}\mathbf{22}\mathbf{.}\mathbf{9}\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{H}\mathbf{=}\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{P}\mathbf{=}\mathbf{30}\mathbf{.}\mathbf{97}\mathbf{u}\mathbf{,}\mathbf{ }\mathbf{O}\mathbf{=}\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{ }\mathbf{u}$

Then add the atomic masses of the constituent atoms.

Molecular mass

$$\begin{gathered} \mathbf{=}\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{Na}\mathbf{+}\mathbf{2}\mathbf{\times }\mathbf{ }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{H}\mathbf{+}\mathbf{ }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{P}\mathbf{+}\mathbf{4}\mathbf{\times }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{O} \\ \mathbf{=}\mathbf{22}\mathbf{.}\mathbf{99}\mathbf{+}\mathbf{2}\left(1.01\right)\mathbf{+}\mathbf{30}\mathbf{.}\mathbf{97}\mathbf{+}\mathbf{4}\left(16.00\right) \end{gathered}$$

Molecular mass $\mathbf{=}\mathbf{119}\mathbf{.}\mathbf{98}\mathbf{ }\mathbf{amu}$.

Step 3: To Write the formula and calculate the molecular mass for Potassium bicarbonate

Potassium is a group 1 element with a charge of +1 and bicarbonate is a polyatomic anion with the formula, ${\mathbf{HCO}}_{\mathbf{3}}^{\mathbf{-}}$

The charges of each ion will just interchange as subscripts and will give its molecular formula.  

data-custom-editor="chemistry" ${\mathbf{K}}^{\mathbf{+}}{\mathbf{HCO}}_{\mathbf{3}}^{\mathbf{-}}\mathbf{\to }{\mathbf{KHCO}}_{\mathbf{3}}$

List the atomic mass of each of the elements present.

$\mathbf{K}\mathbf{=}\mathbf{39}\mathbf{.}\mathbf{10}\mathbf{u}\mathbf{ }\mathbf{H}\mathbf{=}\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{u}\mathbf{ }\mathbf{C}\mathbf{=}\mathbf{12}\mathbf{.}\mathbf{01}\mathbf{u}\mathbf{ }\mathbf{O}\mathbf{=}\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{u}$

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

Molecular mass

$$\begin{gathered} \mathbf{=}\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{K}\mathbf{+}\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{H}\mathbf{+}\mathbf{ }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{C}\mathbf{+}\mathbf{3}\mathbf{\times }\mathbf{ }\mathbf{Atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{O} \\ \mathbf{=}\mathbf{39}\mathbf{.}\mathbf{10}\mathbf{+}\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{+}\mathbf{12}\mathbf{.}\mathbf{01}\mathbf{+}\mathbf{3}\left(16.00\right) \end{gathered}$$

Molecular mass $\mathbf{=}\mathbf{100}\mathbf{.}\mathbf{12}\mathbf{ }\mathbf{amu}\mathbf{.}$