Gas Law Problems a) An sample of unknown gas has a mass of 0.125 g and a volume
ID: 529092 • Letter: G
Question
Gas Law Problems a) An sample of unknown gas has a mass of 0.125 g and a volume of 111 mL at 751 mmHg and 27.5 degree C. If the gas is known to be a molecular element, what is the identity of the unknown gas? b) A sample of magnesium is reacted with hydrochloric acid and hydrogen gas is produced and collected over water: Mg(s) 2 HCl(aq) rightarrow MgCl_2(aq) + H_2(g) If 85.0 mL of hydrogen gas is produced at a temperature of 17.5 degree C and a barometric pressure is 761.5 mm Hg, How many grams of hydrogen have been produced? At this temperature, the vapor pressure of water is 14.8 mm Hg.Explanation / Answer
Ans 8 a)
According to ideal gas law
pV = nRT
where p is pressure in atm = 0.98816 atm , V is volume in L = 0.111 L , R is universal gas constant = 0.08206 latm/mol K , T is temperature in Kelvin = 300.65K , n is number of moles of gas
Putting all the terms in the equation
0.98816 x 0.111 = n x 0.08206 x 300.65
n= 0.0044 moles
n = 0.125 g / M
M = 28.11 g/ mol
So the gas corresponds to the dinitrogen .
b) using the same law
pV = nRT
1.002 x 0.085 = n x 0.08206 x 290.65
n = 0.0036 moles
1 mole of hydrogen gas = 2 g/ mol
0.0036 moles = 0.0072 grams
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