Question

A tank contains 7.0 moles of a mixture of nitrogen gas and oxygen gas. The total

pressure exerted by the gas mixture is 530 kPa. The partial pressure exerted by the
oxygen is 140 kPa. How many moles of NITROGEN gas are present in the tank?

Answer 1

5.2 mol

Step-by-step explanation:

Step 1: Given data

• Total number of moles (n): 7.0 mol

• Total pressure (P): 530 kPa

• Partial pressure of oxygen (pO₂): 140 kPa

Step 2: Calculate the mole fraction of oxygen

We will use the following expression.

pO₂ = P × X(O₂)

X(O₂) = pO₂ / P

X(O₂) = 140 kPa / 530 kPa

X(O₂) = 0.264

Step 3: Calculate the moles of oxygen

We will use the definition of mole fraction of oxygen.

X(O₂) = n(O₂) / n

n(O₂) = X(O₂) × n

n(O₂) = 0.264 × 7.0 mol

n(O₂) = 1.8 mol

Step 4: Calculate the moles of nitrogen

The total number of moles is equal to the sum of moles of the individual gases.

n(O₂) + n(N₂) = n

n(N₂) = n - n(O₂)

n(N₂) = 7.0 mol - 1.8 mol

n(N₂) = 5.2 mol