Question

The reaction of solid aluminum with hydrochloric acid is used to make hydrogen gas in a laboratory experiment. The reaction is 2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g). The hydrogen gas is collected over water. How many moles of hydrogen gas were formed when 75.3 mL is collected at 20.0oC and 768.0 torr pressure? The vapor pressure of water at this temperature is 17.5 torr.

Answer 1

Answer:

0.003088 moles of hydrogen gas were formed .

Explanation:

Pressure at which hydrogen  gas is collected at 20°C = 768.0 Torr

Vapor pressure of water at 20°C = 17.5 Torr

Total pressure = Vapor pressure of water + Partial pressure of hydrogen gas

Partial pressure of hydrogen gas:

Total pressure - Vapor pressure of water

= 768.0 Torr - 17.5 Torr = 750.5 Torr = 0.987 atm

(1 Torr = 0.001315 atm)

Pressure of hydrogen gas =P = 0.986 atm

Temperature at which gas was collected ,T= 20°C = 293.15 K

Volume of the gas ,V= 75.3 mL = 0.0753 L

Moles of hydrogen gas = n

PV=nRT (An ideal gas equation)

$n=\frac{PV}{RT}=\frac{0.987 atm\times 0.0753 L}{0.0821 atm L/mol K\times 293.15 K}=0.003088 mol$

0.003088 moles of hydrogen gas were formed .