Zinc metal is added to hydrochloric acid to generate hydrogen gas and is collected over a liquid whose 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 0.788 atm. Determine the number of moles of hydrogen gas present in the sample.

Question

Quizplus · Accepted Answer

First, we need to find the partial pressure of hydrogen gas in the sample. To do this, we subtract the vapor pressure of the collected liquid from the total pressure of the sample:

partial pressure of hydrogen gas = total pressure - vapor pressure
partial pressure of hydrogen gas = 0.788 atm - 0.018 atm
partial pressure of hydrogen gas = 0.770 atm

Next, we can use the Ideal Gas Law to find the number of moles of hydrogen gas present:

PV = nRT
n = PV/RT

We know the pressure (0.770 atm), volume (1.7 L), and temperature (20.0°C = 293 K), so we can solve for n:

n = (0.770 atm)(1.7 L) / (0.0821 L·atm/mol·K)(293 K)
n = 0.0540 mol

Therefore, the number of moles of hydrogen gas present in the sample is 0.0540 mol, which corresponds to choice D.

Zinc Metal Is Added to Hydrochloric Acid to Generate Hydrogen