Question

When 83.3 grams of phosphorus pentachloride react with an excess of water, as shown in the unbalanced chemical equation below, how many moles of hydrochloric acid will be produced?

PCl5 + H2O yields H3PO4 + HCl

0.4 moles
1.0 moles
1.6 moles
2.0 moles

Answer 1

2.0 moles. (83.3g / 208 [grams/moles] *5 [from balancing] = around 2

Answer 2

The answer is 2 moles of HCl

Step-by-step explanation:

To solve we have to adjust the equation:

PCl5 + 4H2O = 5HCl + H3PO4

we calculate the molecular weights of the compounds using the periodic table:

P = 30.97 g/mol

Cl = 5x35.45 = 177.25 g/mol

H = 1 g/mol

PCl5 = 30.97+177.25 = 208.22 g/mol

HCl =1+35.45 = 36.45 g/mol

we use a rule of three to calculate the mass of hydrochloric acid that forms when the 83.3 phosphorus pentachloride reacts:

208.22 g PCl5-----------------182.25 g HCl

83.3 g PCl5------------------------X g HCl

Clearing the X, we have:

X g HCl = (83.3x182.25)/208.22 = 72.91 g HCl

we calculate the moles of hydrochloric acid:

Moles of HCl = 72.91/36.45 = 2 moles of HCl