A0.040 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 25â°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 25â°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

The correct answer is option B.

Explanation:

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

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

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

(ideal gas equation )

n =

moles of hydrogen are produced in this reaction.

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