# Dalton’s Law Formula | Problems (With Answers)

Dalton’s law formula states that the total pressure (PTotal) of the mixture of gases is equal to the sum of partial pressure of individual gases in the mixture. Here’s the formula of dalton’s law: PTotal = P1 + P2 + P3 + …. Pn

Let’s solve some problems based on this formula, so you’ll get a clear idea.

## Dalton’s Law Practice Problems

Problem 1: A mixture of nitrogen, oxygen and helium is filled in a cylinder. This mixture of these three gases exerts a total pressure of 12 atm on the wall of a cylinder. If the partial pressures of nitrogen and oxygen are 2 atm and 3 atm respectively, then calculate the partial pressure of helium.

Solution:

Given data:
Total pressure of the gas, PTotal = 12 atm
Partial pressure of the nitrogen gas, P1 = 2 atm
Partial pressure of the oxygen gas, P2 = 3 atm
Partial pressure of the helium gas, P3 = ?

Using the formula of dalton’s law,
PTotal = P1 + P2 + P3 + …. Pn
PTotal = P1 +P2 + P3 (Because, a mixture is made up of three gases)
12 = 2 + 3 + P3
P3 = 12 – 5
P3 = 7 atm

Therefore, the partial pressure of the helium gas is 7 atm.

Problem 2: A solid container contains a mixture of four gases whose partial pressures are 4 atm, 3 atm, 5 atm and 8 atm respectively. Calculate the total pressure of the gas.

Solution:

Given data:
Partial pressure of the gas 1, P1 = 4 atm
Partial pressure of the gas 2, P2 = 3 atm
Partial pressure of the gas 3, P3 = 5 atm
Partial pressure of the gas 4, P4 = 8 atm
Total pressure of the gas, PTotal = ?

Using the formula of dalton’s law,
PTotal = P1 + P2 + P3 + …. Pn
PTotal = P1 +P2 + P3 + P4 (Because, a mixture is made up of four gases)
PTotal = 4 + 3 + 5 + 8
PTotal = 20 atm

Therefore, the total pressure of the gas is 20 atm.

Problem 3: A mixture of hydrogen gas and argon gas is filled in one container. Calculate the partial pressure of the argon gas, if the total pressure of the gas is 9 atm and the partial pressure of the hydrogen gas is 6 atm.

Solution:

Given data:
Partial pressure of the argon gas, P1 = ?
Total pressure of the gas, PTotal = 9 atm
Partial pressure of the hydrogen gas, P2 = 6 atm

Using the formula of dalton’s law,
PTotal = P1 + P2 + P3 + …. Pn
PTotal = P1 +P2 (Because, a mixture is made up of two gases)
9 = P1 + 6
P1 = 9 – 6
P1 = 3 atm

Therefore, the partial pressure of the argon gas is 3 atm.

Problem 4: Five gases filled in the container exerts a 24 atm of total pressure on the walls of the container. The partial pressures of the four gases are 2 atm, 5 atm, 6 atm and 8 atm respectively. Calculate the partial pressure of the fifth gas.

Solution:

Given data:
Total pressure of the gas, PTotal = 24 atm
Partial pressure of the gas 1, P1 = 2 atm
Partial pressure of the gas 2, P2 = 5 atm
Partial pressure of the gas 3, P3 = 6 atm
Partial pressure of the gas 4, P4 = 8 atm
Partial pressure of the gas 5, P5 = ?

Using the formula of dalton’s law,
PTotal = P1 + P2 + P3 + …. Pn
24 = 2 +5 + 6 + 8 + P5 (Because, a mixture is made up of five gases)
24 = 21 + P5
P5 = 24 – 21
P5 = 3 atm

Therefore, the partial pressure of the fifth gas is 3 atm.

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