Question

A chemist collects hydrogen gas over water in an apparatus shown below. If the eudiometer reads 17.3800 mL of gas and has a total pressure of

95.090 mm Hg at 15.0°C, then how many moles of hydrogen gas were collected? (the vapor pressure of water at 15.0°C is 12.8 mm Hg)

Answer 1

7.93 × 10⁻⁵ mol

Step-by-step explanation:

Step 1: Calculate the pressure of hydrogen

The total pressure is the sum of the partial pressures of hydrogen and water vapor.

P = pH₂ + pH₂O

pH₂ = P - pH₂O

pH₂ = 95.090 mmHg - 12.8 mmHg = 82.3 mmHg

We can convert it to atm using the conversion factor 1 atm = 760 mmHg.

82.3 mmHg × 1 atm/760 mmHg = 0.108 atm

Step 2: Convert 15.0 °C to Kelvin

We will use the following expression.

K = °C + 273.15 = 15.0 + 273.15 = 288.2 K

Step 3: Calculate the moles of hydrogen

We will use the ideal gas equation.

P × V = n × R × T

n = P × V / R × T

n = 0.108 atm × 0.0173800 L / (0.0821 atm.L/mol.K) × 288.2 K

n = 7.93 × 10⁻⁵ mol