Phosphorus pentachloride reacts with water to form hydrochloric acid and phosphoric acid. How many total moles of acid are formed when starting with 4.5 g of PCl₅ and excess H₂O?
PCl₅ + 4H₂O $\rarr$ 5HCl + H₃PO₄

Question

Phosphorus pentachloride reacts with water to form hydrochloric acid and phosphoric acid. How many total moles of acid are formed when starting with 4.5 g of PCl₅ and excess H₂O?
PCl₅ + 4H₂O

\rarr

5HCl + H₃PO₄

Quizplus · Accepted Answer

First, we need to determine the limiting reagent. Using the balanced equation, we can see that one mole of PCl5 reacts with four moles of water to form five moles of acid. 
Moles of PCl5 = mass/molar mass = 4.5g/208.2g/mol = 0.0216 mol. 
Since PCl5 is the limiting reagent, it will produce 5 times more moles of acid. 
Total moles of acid = 5 x 0.0216 mol = 0.108 moles HCl + 0.108 moles H3PO4. However, HCl is also produced by the excess water. Since we have an excess of water, all of the HCl produced by the reaction will remain in solution as aqueous HCl. Therefore, the total moles of acid formed is 0.108 moles or approximately 0.13 moles. Choice C is the best answer.

Phosphorus Pentachloride Reacts with Water to Form Hydrochloric Acid and Phosphoric