Chapter 17, Problem 11STP

Interpretation Introduction

Interpretation:

The molar ratio of water to phosphoric acid is to be calculated.

Concept introduction

Molar ratio tells the proportion of reactants and products which are used and formed in a chemical reaction. This ratio is calculated from the coefficients of a balanced chemical equation.

Answer to Problem 11STP

The molar ratio of water to phosphoric acid in a given reaction is $\text{4:1}$.

Explanation of Solution

The given reaction is as follows:

${\text{PCl}}_{\text{5}}{\text{+ H}}_{\text{2}}\text{O }\to {\text{ H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{+ HCl}$

The molar ratio of a balanced chemical equation is the proportion of reactants and products which are used in a balanced chemical equation.

So, the balanced equation is

${\text{PCl}}_{\text{5}}{\text{+ 4H}}_{\text{2}}\text{O }\to {\text{ H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{+ 5HCl}$

Explanation:

Left side Right side

$\begin{array}{l}\text{P=1 P =1}\hfill \\ \text{Cl =5 Cl =1}\hfill \\ \text{H=2 H=3+1}\hfill \\ \text{O=1 O= 4}\hfill \end{array}$

Now start balancing the easiest element such as $\text{Cl}$

Left side Right side

$\begin{array}{l}\text{P=1 P =1}\hfill \\ \text{Cl =5 Cl = 1×5 = 5}\hfill \\ \text{H=2 H= 3+ }\left(\text{1×5}\right)\text{ = 8}\hfill \\ \text{O=1 O = 4}\hfill \end{array}$

Now equation becomes

${\text{PCl}}_{\text{5}}{\text{+ H}}_{\text{2}}{\text{O = H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{+ 5HCl}$

Now balancing the H atom

Left side Right side

$\begin{array}{l}\text{P=1 P=1}\hfill \\ \text{Cl=5 Cl= 1×5 =5}\hfill \\ \text{H= 2×4 = 8 H= 3+ }\left(\text{1×5}\right)\text{ = 8}\hfill \\ \text{O= 1×4= 4 O= 4 }\hfill \end{array}$

So, finally the given equation is balanced

${\text{PCl}}_{\text{5}}{\text{+ 4H}}_{\text{2}}\text{O }\to {\text{ H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{+ 5HCl}$

Hence, in this way a given equation becomes balanced.

The proportion of water and phosphoric acid are 4 and 1 after the balancing process.

The molar ratio of water and phosphoric acid is $\text{4:1}$.

Conclusion

The molar ratio of water and phosphoric acid is $\text{4:1}$.