queston in description

Question

How many liters of Dihydrogen gas will form at 5 C and 752 torr when 175.0 cm³ of a 1.07 M Phosphoric Acid reacts with 2.5g of Zinc Metal Forming Zinc Phosphate as the other product?

Answer 1

First, you must write a correctly balanced equation for this reaction:

2H₃PO₄ + 3Zn ==> Zn₃(PO₄)₂ + 3H₂

moles of H3PO4 present = 1.07 moles/L x 0.175 L = 0.1873 moles

moles Zn present = 2.5 g x 1 mole/65.38 g = 0.0382 moles 

Which reactant is limiting?  From the mole ratios of the balanced equation, it is clear that Zn is limiting.

Moles H2 produced = 0.0382 moles Zn x 3 moles H2/3 moles Zn = 0.0382 moles H2 gas

Liters of H2 gas:  PV = nRT and V = nRT/P (T=5+273=278K and P = 752/760 = 0.989 atm)

V = (0.0382)(0.0821)(278)/0.989 = 0.882 liters