Question

If $P^{\circ}$ and $P$ are the vapour pressure of solvent and solution $n_{1}$ and $n_{2}$ are the moles of solute and solvent then

• A. $P ^{\circ}= P \left(\frac{ n _{2}}{ n _{1}+ n _{2}}\right)$
• B. $P = P ^{\circ}\left(\frac{ n _{2}}{ n _{1}+ n _{2}}\right)$
• C. $P ^{\circ}= P \left(\frac{ n _{1}}{ n _{1}+ n _{2}}\right)$
• D. $P ^{\circ}= P \times n _{1}$

Answer 1

Answer: (B)

$P=P^{0} x $
$P^{\circ}=$ solvent
$P=P^{0}\left(\frac{n_{2}}{n_{1}+n_{2}}\right)$
$x=$ mole fraction of solvent $=\frac{\text { Moles of solvent }}{\text { moles of solute }+\text { moles of solvent }}$
$=\frac{n_{2}}{n_{1}+n_{2}}$