Molality : It is defined as the number o...

Molality : It is defined as the number of moles of the solute present in 1 kg of the solvent. It is denoted by 'm'.
Molality(m)=`"Number of moles of solute"/"Number of kilo-grams of the solvent"`
Let `w_A` grams of the solute of molecular mass `m_A` be present in `w_a` grams of the solvent, then
Molality (m)=`w_A/(m_Axxw_B)xx100`
Realtion between mole fraction and Molality :
`X_A=n/(N+n) and X_B=N/(N+n)`
`X_A/X_B=n/N="Moles of solute"/"Moles of solvent"=(w_Axxm_B)/(w_Bxxm_A)`
`(X_Axx1000)/(X_Bxxm_B)=(w_Axx1000)/(w_Bxxm_A)=m or (X_Axx1000)/((1-X_A)m_B)=m`
What is the molality of final solution obtained in the above problem

1.422

14.22

15.22

None

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Verified by Experts

The correct Answer is:

Mole of solute=`(300xx0.3+500xx0.4)/40=7.25`
Mass of solvent=800-290=510
Molality`=7.25/510xx1000=14.22`

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