Vapour Pressure Of Liquid Solutions

Determining Molar Mass Using Raoult's Law

Given:

• Vapour pressure of pure benzene,
• Vapour pressure of solution,
• Mass of solute = 1.0 g
• Mass of benzene = 39.0 g
• Molar mass of benzene = 78 g/mol

Raoult's Law:

Let molar mass of solute =

Then, moles of solute =

Moles of benzene =

Now, plug values into the formula:

Correct Answer: 340 g mol^-1

The dipole moment of a molecule is a vector quantity which depends on the magnitude of the bond dipoles and the angle between them. Molecules like NH have a higher dipole moment because of the following reasons:
- NH (Ammonia) has a trigonal pyramidal structure, where the nitrogen atom has a lone pair of electrons that contributes to the dipole moment. The dipoles do not cancel each other out, leading to a net dipole moment.
- NF , BeF , CCl , and BF are all molecules with a symmetric shape (tetrahedral or linear). In these molecules, the dipole moments of individual bonds cancel each other out, resulting in a net dipole moment of zero or a smaller dipole moment compared to NH .
Therefore, the molecule with the highest dipole moment is NH .

Lindlar’s catalyst is used for the hydrogenation of alkynes to cis-alkenes. This catalyst is specifically designed to selectively hydrogenate alkynes without reducing them to alkanes. It does this by allowing the addition of hydrogen across the triple bond to form a cis-alkene.
In the given reactions:
- Option (A): This is a typical hydrogenation reaction, but it is not a case where Lindlar's catalyst is used.
- Option (B): This reaction involves the reduction of a ketone to an alcohol, which does not require Lindlar's catalyst.
- Option (C): This reaction involves the reduction of a nitro group to an amine, which also does not require Lindlar's catalyst.
- Option (D): This is a reduction of an aldehyde to a primary alcohol, which does not involve Lindlar’s catalyst.
- Option (E): This reaction shows the hydrogenation of an alkyne ( ) to a cis-alkene ( ), which is exactly the type of reaction Lindlar's catalyst is used for.
Thus, the correct answer is option (E), .