22. Zinc metal is added to hydrochloric acid to generate hydrogen gas and is col

Question

22. Zinc metal is added to hydrochloric acid to generate hydrogen gas and is collect vapor pressure is the same as that of pure water at 20.0°C (18 torr). The volume of the mixture is 1.7 L, and its total pressure is 0.987 atm. Determine the number of moles of hydrogen gas present in the sample. ed over a liquid whose 23. How many moles of 02(g) are needed to react completely with 38.6 L of CHafg) at STP to produce CO.(g) and H20(g) according to the following reaction? C (g) +2O2 (g) CO2 (g)+2H2O(g)

Explanation / Answer

(22)

Zn + 2HCl ------> ZnCl2 + H2

vapor pressure of the liquid = 18 torr

Volume of mixture = 1.7 L

total pressure = 0.987 atm x 760 torr/1 atm = 750.12 torr

From Dalton's law of partial pressures...

Total pressure = partial pressure of liquid + partial pressure of hydrogen has

partial pressure of hydrogen gas = Total pressure - partial pressure of liquid

partial pressure of hydrogen gas = 750.12 torr - 18 torr = 732.12 torr x 1atm/760 torr = 0.963 atm

temperature = 20 + 273 = 293K

since the gas covers the total volume, so volume of Hydrogen gas would also be 1.7 L

from ideal gas equation, PV = nRT

n = PV/RT

n = (0.963 x 1.7)/(0.0821 x 293)

n = 0.0681 moles (Answer)

(23)

CH4(g) + 2O2(g) -----> CO2(g) + 2H2O(g)

we know that, at STP, volume of 1 mol of a gas is 22.4 L.

So, 38.6 L of CH4 x 1mol/22.4 L = 1.72 mol of CH4

Now to calculate the moles of O2, we will use the stoichiometry...

1.72 mol of CH4 x 2 mol of O2/1 mol of CH4 = 3.44 mol of O2

So, the answer is 3.44 mol of O2.

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