2. An active metal (an oxidation state is +3) reacts with hydrochloric acid (HCI

Question

2. An active metal (an oxidation state is +3) reacts with hydrochloric acid (HCI) to form nydrogen gas. The gas is collected in a gas buret. The following during the study data were obtained Mass of active metal = 0.225 g Volume of gas in buret = 96.52 mL Water height differential-156 mm apor pressure of water in the wet hydrogen gas- 22.4 mm Hg Barometric pressure 759 mm Hg Temperature 25°C You are given the following conversion factors and universal gas constant. 1.00 mm Hg = 13.6 mm H2O 1.00 atm 760 mm Hg °C + 273 = K R = 0.08206 L' atm/K-mol (a) Calculate pressure of the wet gas in the buret Pgas. Show your calculations. (2 points) (b) Calculate partial pressure of dry hydrogen PH2 in the buret. Show your calculations (2 points) 723.13 mm H 759-11.47

Explanation / Answer

total pressure of gas = 741.73 mm Hg

Volume of gas = 96.52/1000 L

Temperature = 25+273 K =298 K

From gas law,

PV = nRT where n is the number of moles of gas.

so, putting the values we get n= 2.92 moles

Now, from Daltons law of partial pressure we have, pi/p = ni/n

pi is the partial pressure of the gas and ni is its number of moles

So for water we have, 22.4/741.73 = ni/2,92

ni = 0.088 moles

So, number of moles of hydrogen = 2.92- 0.088 = 2.83 moles

So, partial pressure of 2.83 moles of hydrogen = 2.83 * 741.73/2.92 = 718.86 mm Hg

Alternatively,

Total pressure = sum of partial pressures of water and hydrogen

or, 741.73 = 22.4 + pH2

or, pH2= 719.33

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