Question

The pressure exerted by saturated water vapour is called aqueous tension. The pressure of the dry gas can be calculated as?
A. ${{\text{P}}_{\text{Dry gas}}}={{\text{P}}_{\text{Total}}}-\text{aqueous tension}$
B. ${{\text{P}}_{\text{Dry gas}}}={{\text{P}}_{\text{Total}}}+\text{aqueous tension}$
C. ${{\text{P}}_{\text{Dry gas}}}={{\text{P}}_{\text{Total}}}\text{/aqueous tension}$
D. ${{\text{P}}_{\text{Dry gas}}}={{\text{P}}_{\text{Total}}}\times \text{aqueous tension}$

Answer 1

Hint: Aqueous tension is actually the pressure of saturated vapours. Saturated vapour is the maximum limit of water vapour that a particular quantity of air can hold at a particular temperature is termed as saturated vapour. Check the properties of aqueous tension and its definition in detail.

Complete answer:
Aqueous tension is the partial pressure of the water vapour present in the moist gas. The partial pressure due to the water vapour mixed with a gas measured over water.
How does the gas become moist? The answer to this question is during experiments, some gases are collected over water; with that the gas during the collection gathers water vapours and becomes moist. This moistness is due to the presence of a small quantity of water vapour caused by evaporation. Therefore, the pressure exerted by this moist gas is the sum of the partial pressures of the dry gas and of the water vapours. This gives rise to aqueous tension.
- The statement is the pressure exerted by moist gas = pressure exerted by dry gas + pressure of aqueous tension. Mathematically, represented as ${{\text{P}}_{\text{moist gas}}}={{\text{P}}_{\text{dry gas}}}+{{\text{P}}_{\text{water vapour}}}$. This pressure of water vapours is given a name aqueous tension. So, the formula is ${{\text{P}}_{\text{Dry gas}}}={{\text{P}}_{\text{Total}}}-\text{aqueous tension}$.
The pressure of the dry gas can be calculated as ${{\text{P}}_{\text{Dry gas}}}={{\text{P}}_{\text{Total}}}-\text{aqueous tension}$.

Hence, the correct answer is option ‘c’.

Note:
​It is specific and definite for each temperature. Aqueous tension is dependent on temperature. It is independent of volume and pressure. Like equilibrium constants, it only depends on temperature. While doing numericals, the pressure of water vapours is not added, that is pressure of dry gas is considered in ideal gas equations numericals.