A mixture of three gases has a total pressure of 786 mmHg. The mixture is 27% gas A and 53% gas B. What is the partial pressure due to the third gas?

212.2 mmHg

417 mmHg

157.2 mmHg

629.8 mmHg

1 answer

To find the partial pressure of the third gas in the mixture, we first need to determine the partial pressures of gases A and B using their respective percentages.

Given:

  • Total pressure, \( P_{\text{total}} = 786 , \text{mmHg} \)
  • Percentage of gas A, \( P_A = 27% \)
  • Percentage of gas B, \( P_B = 53% \)
  1. Calculate the partial pressure of gas A: \[ P_A = \frac{27}{100} \times P_{\text{total}} = 0.27 \times 786 , \text{mmHg} = 212.22 , \text{mmHg} \]

  2. Calculate the partial pressure of gas B: \[ P_B = \frac{53}{100} \times P_{\text{total}} = 0.53 \times 786 , \text{mmHg} = 416.58 , \text{mmHg} \]

  3. Use Dalton's law of partial pressures, which states that the total pressure is the sum of the partial pressures: \[ P_{\text{total}} = P_A + P_B + P_C \] Where \( P_C \) is the partial pressure of the third gas. Rearranging the equation gives: \[ P_C = P_{\text{total}} - P_A - P_B \]

  4. Substitute the values to find \( P_C \): \[ P_C = 786 , \text{mmHg} - 212.22 , \text{mmHg} - 416.58 , \text{mmHg} \] \[ P_C = 786 - 212.22 - 416.58 = 157.2 , \text{mmHg} \]

Therefore, the partial pressure due to the third gas is 157.2 mmHg.