A sample of gas is collected over water at at a barometric pressure of 751 mm Hg (vapour pressure of water at is 21 mm Hg).The partial pressure of gas in the sample collected is

Options

A. 21 mm Hg
B. 751 mm Hg
C. 0.96 atm
D. 1.02 atm

Answer

To find the partial pressure of the gas in the sample collected over water, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Total Pressure**: The total pressure of the gas collected over water is given as 751 mm Hg. This pressure includes both the pressure of the gas and the vapor pressure of the water.

2. **Identify the Vapor Pressure of Water**: The vapor pressure of water at the given temperature is provided as 21 mm Hg. This is the pressure exerted by the water vapor in the container.

3. **Calculate the Partial Pressure of the Gas**: To find the partial pressure of the gas, we need to subtract the vapor pressure of water from the total pressure:
\[ \text{Partial Pressure of Gas} = \text{Total Pressure} - \text{Vapor Pressure of Water} \]
Substituting the values:
\[ \text{Partial Pressure of Gas} = 751 \, \text{mm Hg} - 21 \, \text{mm Hg} = 730 \, \text{mm Hg} \]

4. **Convert to Atmospheres**: Since the problem may require the answer in atmospheres (atm), we convert the pressure from mm Hg to atm. We know that 1 atm = 760 mm Hg. Therefore:
\[ \text{Partial Pressure in atm} = \frac{730 \, \text{mm Hg}}{760 \, \text{mm Hg/atm}} \approx 0.96 \, \text{atm} \]

### Final Answer:
The partial pressure of the gas in the sample collected is approximately **0.96 atm**.

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