Chapter 9, Problem 63A

Interpretation Introduction

Interpretation: The element X with molecular formula ${\text{X}}_{\text{4}}$ that combines with HCl to form ${\text{XCl}}_{\text{3}}$ needs to be determined, with the help of balance chemical equation.

Concept Introduction: A chemical reaction involves the conversion of reactant to product by breaking and making of chemical bonds.

There can be more than one reactant molecules involve in a chemical reaction to form the products. The reactant which is present in limited amount in a chemical reaction is called as limiting reactant.

Answer to Problem 63A

X = P ( phosphorus)

Explanation of Solution

Given information:

Mass of ${\text{H}}_{\text{2}}$ formed during the reaction = 24.0 g

Mass of ${\text{X}}_{\text{4}}$ consumed = 248 g

The balance chemical equation of ${\text{X}}_{\text{4}}$ with HCl to form ${\text{XCl}}_{\text{3}}$ and ${\text{H}}_{\text{2}}$ can be written as:

  ${\text{X}}_{\text{4}}\text{+ 12 HCl}\stackrel{}{\to }{\text{ 4 XCl}}_{\text{3}}{\text{+ 6 H}}_{\text{2}}$

Mass of ${\text{H}}_{\text{2}}$ formed during the reaction = 24.0 g

Mass of ${\text{X}}_{\text{4}}$ consumed = 248 g

Molar mass of ${\text{H}}_{\text{2}}$ = 2.00 g

Calculate moles of ${\text{H}}_{\text{2}}$ :

  ${\text{Moles of H}}_{\text{2}}\text{= }\frac{\text{24}\text{.00}}{\text{2}\text{.00 g/mol}}\text{=12}\text{.0 moles}$

From the balance chemical equation:

1 mole of ${\text{X}}_{\text{4}}$ = form 6 mole of ${\text{H}}_{\text{2}}$

Calculate moles of ${\text{X}}_{\text{4}}$ :

  $\text{12}{\text{.0 moles H}}_{\text{2 }}\text{×}\frac{{\text{1 mole X}}_{\text{4}}}{{\text{6 mole H}}_{\text{2 }}}\text{ = 2}{\text{.0 moles X}}_{\text{4}}$

Calculate the molar mass of ${\text{X}}_{\text{4}}$ :

  $\begin{array}{l}{\text{Molar mass of X}}_{\text{4}}=\frac{\text{248 g}}{\text{2 mole}}\text{ = 124 g/mol }\\ \text{Molar mass of X =}\frac{\text{ 124 g/mol }}{\text{4}}\text{ = 31 g/mol}\end{array}$

The element with 31 g/mol molar mass of phosphorus.

Conclusion

Thus, the element X is P ( phosphorus) .