Question

A 0.040 g piece of magnesium is placed in a beaker of hydrochloric acid. Hydrogen gas is generated according to the following equation:_______

Mg (s) + 2 HCl (aq) â MgCl2 (aq) + H2 (g)
The gas is collected over water at 25°C, and the gauge pressure during the experiment reads 784 mmHg.The gas displaces a volume of 100 mL. The vapor pressure of water at 25°C is approximately 24.0 mmHg. Based on this data, how many moles of hydrogen are produced in this reaction?
A. 4.04 Ã 10-5 moles hydrogen
B. 4.09 Ã 10-3 moles hydrogen
C. 3.07 Ã 10-2 moles hydrogen
D. 3.11 moles hydrogen

Answer 1

The correct answer is option B.

Step-by-step explanation:

`Mg (s) + 2 HCl (aq)\rightarrow  MgCl_2 (aq) + H_2 (g)`

Temperature of the hydrogen gas = T = 25°C=25+273 K= 298 K

Pressure of hydrogen gas ,P = gauge pressure - vapor pressure of water

`P=784 mmHg-24 mmHg= 760 mmHg`

`1 atm = 760 mmHg`

Volume of the hydrogen gas = V =100 mL =100 × 0.001 L= 0.1 L

(1 mL = 0.001 L)

Moles of hydrogen gas = n

`PV=nRT` (ideal gas equation )

`n=(PV)/(RT)=(1 atm * 0.1 L)/(0.0821 atm l/mol K* 298 K)`

n =
`4.09* 10^(-3) moles`

`4.09* 10^(-3)`moles of hydrogen are produced in this reaction.