Chapter 8, Problem 1SAQ

Sulfur and fluorine react to form sulfur hexafluoride according to the reaction shown here. How many mol of ${\text{F}}_2$

are required to react completely with 2.55 mol of S? $S\left(s\right)+3{\text{F}}_2\left(g\right)\to {\text{SF}}_6\left(g\right)$

a. 0.85 mol ${\text{F}}_2$

b. 2055 mol ${\text{F}}_2$

c. 7.65 mol ${\text{F}}_2$

d. 15.3 mol ${\text{F}}_2$

Interpretation Introduction

Interpretation: The number of mol of $F_2$ that would be required to react completely with $2.55mol$ of $S$ in the following reaction is to be determined.

$\text{S}\left(\text{s}\right)+3{\text{F}}_{\text{2}}\left(\text{g}\right)\to {\text{SF}}_{\text{6}}\left(\text{g}\right)$

Concept Introduction: When mole of one reactant is given, then apply mole–mole stoichiometric relationship between the moles of the reactants.

Answer to Problem 1SAQ

Correct answer: For complete reaction with $2.55\text{ mol}$ of sulfur, $7.65\text{ mol}$ of fluorine is required.

Therefore, option (c) is correct.

Explanation of Solution

Reason for correct option:

The reaction is given as follows:

$\text{S}\left(\text{s}\right)+3{\text{F}}_{\text{2}}\left(\text{g}\right)\to {\text{SF}}_{\text{6}}\left(\text{g}\right)$

From the above chemical reaction, it is clear that 1 mole of $\text{S}$ reacts with 3 moles of ${\text{F}}_{\text{2}}$. This can be expressed in ratio in terms of moles as follows:

$1{\text{ mol S:3 mol F}}_2$

Thus, to calculate the moles of fluorine from the given moles of sulfur, the conversion factor used will be $\frac{{\text{3 mol F}}_2}{1\text{ mol S}}$.

Multiply the conversion factor with the given $2.55\text{ mol}$ of sulfur, cancelling units to get the desired quantity.

Hence

$2.55\cancel{\text{mol S}}\times \frac{{\text{3 mol F}}_2}{1\cancel{\text{mol S}}}=7.65{\text{ mol F}}_2$

As the given value is in three significant figures, the final answer should also be in three significant figures. Therefore, the final answer will be $7.65{\text{ mol F}}_2$.

Hence, option (c) is correct.

Reasons for incorrect options:

Option (a) is incorrect because according to the above calculation, $0.85{\text{ mol F}}_2$ cannot be obtained. So, it is a wrong answer.

Option (b) is incorrect because according to the above calculation, $2.55{\text{ mol F}}_2$ cannot be obtained. So, it is a wrong answer.

Option (d) is incorrect because according to the above calculation, $15.3{\text{ mol F}}_2$ cannot be obtained. So, it is a wrong answer.

Hence, options (a), (b), and (d) are incorrect.