Chapter 11, Problem 49A

Solid silicon dioxide, often called silica, reacts with hydrofluoric acid (HF) solution to produce the gas silicon tetrafluoride and water.

a. Write the balanced chemical equation for the reaction.
b. List three mole ratios, and explain how you would use them in stoichiometric calculations.

Interpretation Introduction

Interpretation:

The balance chemical equation for the reaction of solid silicon dioxide (silica) with hydrofluoric acid (HF) solution to produce the gas silicon tetrafluoride and water needs to be determined.

Concept introduction:

The mole concept provides the relation between moles, mass and molar mass. The mathematical expression of mole concept can be written as:

$\text{Mole =}\frac{\text{Mass}}{\text{Molar mass}}$

1 mole of any substance contains $\text{6}\text{.022 }\times {\text{ 10}}^{\text{23}}$ number of particles or atoms or molecules.

Answer to Problem 49A

${\text{Pb(NO}}_{\text{3}}{\text{)}}_{\text{2}}{}_{\text{(aq)}}{\text{ + 2 HCl}}_{\text{(aq)}}\stackrel{}{\to }{\text{PbCl}}_{\text{2}}{}_{\text{(s) }}{\text{ + 2 HNO}}_{\text{3}}{}_{\text{(aq)}}$

Explanation of Solution

The reaction of solid silicon dioxide (silica) with hydrofluoric acid (HF) solution produces the gas silicon tetrafluoride and water. The chemical formula of reactant and products are:

Silica = ${\text{SiO}}_{\text{2}}$

Hydrofluoric acid = HF

Silicon tetrafluoride = ${\text{SiF}}_{\text{4}}$

Water = ${\text{H}}_{\text{2}}\text{O}$

Thus the balance chemical equation must be:

${\text{SiO}}_{\text{2}}{}_{\text{(s)}}{\text{+ 4 HF}}_{\text{(aq)}}\stackrel{}{\to }{\text{ SiF}}_{\text{4}}{}_{\text{(g)}}{\text{+ 2 H}}_{\text{2}}{\text{O}}_{\text{(l)}}$

Interpretation Introduction

(b)

Interpretation:

The six mole rations for the reaction solid silicon dioxide (silica) with hydrofluoric acid (HF) solution to produce the gas silicon tetrafluoride and water needs to be determined.

Concept introduction:

A chemical reaction involves the conversion of certain molecules (reactant) to new substance (product) by bond breaking and making. One of the reactants, which is present in limited amount and determines the amount of product is known as limiting reactant. Whereas another reactant is known as excess reactant.

Answer to Problem 49A

$\begin{array}{l}{\text{SiO}}_{\text{2}}{}_{\text{(s)}}{\text{+ 4 HF}}_{\text{(aq)}}\stackrel{}{\to }{\text{ SiF}}_{\text{4}}{}_{\text{(g)}}{\text{+ 2 H}}_{\text{2}}{\text{O}}_{\text{(l)}}\\ \frac{\text{4 moles HF}}{{\text{1 moles SiO}}_{\text{2}}}{\text{ = gives amount of HF which will react with SiO}}_{\text{2}}\\ \frac{{\text{1 mole SiF}}_{\text{4}}}{{\text{1 moles SiO}}_{\text{2}}}{\text{= gives amount of SiF}}_{\text{4}}{\text{ which will form with SiO}}_{\text{2}}\\ \frac{{\text{2 moles H}}_{\text{2}}\text{O}}{{\text{1 mole SiF}}_4}={\text{gives amount of H}}_{\text{2}}{\text{O which will form with SiF}}_4\end{array}$

Explanation of Solution

The balance chemical equation for solid silicon dioxide (silica) with hydrofluoric acid (HF) solution to produce the gas silicon tetrafluoride and water can be written as:

${\text{SiO}}_{\text{2}}{}_{\text{(s)}}{\text{+ 4 HF}}_{\text{(aq)}}\stackrel{}{\to }{\text{ SiF}}_{\text{4}}{}_{\text{(g)}}{\text{+ 2 H}}_{\text{2}}{\text{O}}_{\text{(l)}}$

The mole ratio relates the moles of reactant with other reactant and product molecules in the balance chemical equation. Thus, one mole ratio relates with other mole ratio. The mole ratio in the given balance reaction must be:

$\begin{array}{l}{\text{SiO}}_{\text{2}}{}_{\text{(s)}}{\text{+ 4 HF}}_{\text{(aq)}}\stackrel{}{\to }{\text{ SiF}}_{\text{4}}{}_{\text{(g)}}{\text{+ 2 H}}_{\text{2}}{\text{O}}_{\text{(l)}}\\ \frac{\text{4 moles HF}}{{\text{1 moles SiO}}_{\text{2}}}{\text{ = gives amount of HF which will react with SiO}}_{\text{2}}\\ \frac{{\text{1 mole SiF}}_{\text{4}}}{{\text{1 moles SiO}}_{\text{2}}}{\text{= gives amount of SiF}}_{\text{4}}{\text{ which will form with SiO}}_{\text{2}}\\ \frac{{\text{2 moles H}}_{\text{2}}\text{O}}{{\text{1 mole SiF}}_4}={\text{gives amount of H}}_{\text{2}}{\text{O which will form with SiF}}_4\end{array}$