Magnesium metal is added to excess acid to generate hydrogen gas, which is collected over water at 25.0°C (vapour pressure of water is 23.8 mm Hg). The volume of the mixture is 0.0251 m3, and its total pressure is 96.4 kPa. Determine the amount of magnesium used in the reaction. Mg + 2H+ --> H2 (g) + Mg2+

Explanation:

PV / RT =  n , n is number of moles

Total pressure  = 96400 Pa

vapour pressure = 23.8 mm of Hg

= .0238 x 13.6 x 10³ x 10 Pa = 3236.8 Pa

Pressure of hydrogen gas P = 96400 - 3236.8

= 93163.2 Pa

n = 93163.2 x .0251 / 8.31 x 298

= .944 moles of hydrogen gas is produced

moles of magnesium reacted = .944

grams of magnesium reacted = .944 x 24 = 22.66 grams .

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