Chapter 10.4, Problem 57PP

(a)

Interpretation Introduction

Interpretation:

The elements present in the compound needs to be identified and its molecular formula needs to be determined.

Concept introduction:

The compound is made up of different atoms and molecules.

These atoms and molecules have charge (valencies) on them to form stable compounds.

A chemical formula is a type of formula for the compound in which different elements are present and shows their relative composition in a compound.

For example $\text{AxBy}$ means x atoms of A and y atoms of B form the compound.

Explanation of Solution

The compound sodium sulphate is formed from sodium and sulphate ion.

Here, sulphate ion is ${\text{SO}}_{\text{4}}{}^{\text{2-}}$ which contains sulfur atom and $4$ oxygen atoms.

Sodium is Na having charge of $+1$

So, the chemical formula is ${\text{Na}}_{\text{2}}{\text{SO}}_{\text{4}}$ which means $\text{2}$ ion stabilizes 1 sulphate ion.

The chemical formula is ${\text{Na}}_{\text{2}}{\text{SO}}_{\text{4}}$

Interpretation Introduction

(b)

Interpretation:

Whether the compound is ionic or covalent needs to be determined.

Concept introduction:

A compound is ionic when formed from complete transfer of election from electropositive atom to electronegative atom. It is formed when electro negativity difference is more.

A compound is covalent when formed from mutual sharing of elections from the atom. It is formed when electro negativity difference is less.

Explanation of Solution

The formula for compounds is ${\text{Na}}_{\text{2}}{\text{SO}}_{\text{4}}$. It is an ionic compound containing ${\text{Na}}^{+}$ and ${\text{SO}}_{\text{4}}{}^{2-}$ ions. The electro negativity difference is more, and Na. (sodium) is electropositive in nature, and hence donates elections to ${\text{SO}}_{\text{4}}{}^{2-}$, and the overall molecule is ionic in nature.

c.

Interpretation Introduction

Interpretation:

The percent by mass of each element in sodium sulphate needs to be calculated.

Concept introduction:

A compound is formed from different composition. By percent of mass, one can find the composition of that element in that compound.

The molecular formula is required in this calculation.

$\text{Percent composition by mass = }\frac{\text{mass of atom }}{\text{total mass of compound}}\times 100$

$\begin{array}{l}\text{Sodium}\Rightarrow 32\cdot 3\%\\ \text{Sulphur}\Rightarrow 22\cdot 5\%\\ \text{Oxygen}\Rightarrow 45\%\end{array}$

Answer to Problem 57PP

$\begin{array}{l}\text{Sodium}\Rightarrow 32\cdot 3\%\\ \text{Sulphur}\Rightarrow 22\cdot 5\%\\ \text{Oxygen}\Rightarrow 45\%\end{array}$

Explanation of Solution

To find percent by mass of each element in compound ${\text{Na}}_{\text{2}}{\text{SO}}_{\text{4}}$

Atomic mass of Na (sodium) $\text{=23 g}$

Atomic mass of Sulphur $\text{=32 g}$

Atomic mass of oxygen $\text{=16 g}$

${\text{Na}}_{\text{2}}{\text{SO}}_{\text{4}}$

Total molar mass of compound $\text{=2}\times 23+32+64$

$\text{=142 g}$

$\text{Mass of atom in the compound}\Rightarrow \text{number of atoms}\times \text{atomic mass of the atom}$

Percentage by mass of sodium $=\frac{2\times 23}{142}\times 100\Rightarrow 32\cdot 3\%$

Percentage by mass of sulphur

$=\frac{32}{142}\times 100\Rightarrow 22\cdot 5\%$

Percentage by mass of oxygen $=\frac{64}{142}\times 100\Rightarrow 45\%$