Applications of Daltons Law

 This law is used in the calculation of following relationships,

(i) Mole fraction of a gas (X1) in a mixture of gas = (Partial pressure of a gas (P1)/Ptotal)

(ii) % of a gas in mixture = (Partial pressure of a gas (P1)/Ptotal )×100

(iii) Pressure of dry gas collected over water : When a gas is collected over water, it becomes moist due to water vapour which exerts its own partial pressure at the same temperature of the gas. This partial perssure of water vapours is called aqueous tension. Thus,      

Pdry gas = Pmoist gas or Ptotal – Pwater vapour  

or Pdrygas = Pmoist gas Aqueous tension (Aqueous tension is directly proportional to absolute temperature)

(iv) Relative humidity (RH) at a given temperature is given by,

RH = (Partial pressure of water in air/Vapour pre ssure of water)

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