Answer:
Because the following rule of solubility:
*'Like dissolves Like"* i.e. a polar molecule dissolves in other polar molecules and non-polar dissovles in non-polar molecules.
The solubility categorization for each compound in water is as follows:
*Insoluble: (ii) toluene, (v) chloroform* , because Toluene is a non-polar molecule while chloroform is a polar molecule. Here are the specific details for each:
*Toluene (C7H8 ):* Toluene consists of a nonpolar benzene ring and a weakly polar methyl group -CH3). Because carbon and hydrogen have very similar electronegativities (2.55) and (2.20), respectively, the C-H bonds are essentially nonpolar. Although there is a slight asymmetry due to the methyl group, it is negligible, making the molecule as a whole nonpolar overall.
*Chloroform (CHCl3):* Chloroform is a polar molecule with a net dipole moment of roughly (1.04D). It has a tetrahedral molecular geometry, composed of three highly electronegative chlorine atoms (Electronegativity = 3.16) and one hydrogen atom (Electronegativity = (2.20) bonded to the central carbon atom. Because chlorine is significantly more electronegative than carbon, electrons are pulled toward the chlorine atoms, creating a region of partial negative charge on one side and a partial positive charge on the hydrogen side.
*Partially soluble: (i) phenol, (vi) pentanol,* because phenol is highly polar while pentanol is moderately polar molecule. (i) *Phenol (C6H5OH)*
Phenol is a highly polar molecule with a net dipole moment of about (1.5D to 1.7D).
Structure: It consists of a polar hydroxyl group (-OH) directly attached to an aromatic benzene ring (phenyl group).
Resonance Effect: The lone pair of electrons on the oxygen atom overlaps with the pi-electrons of the benzene ring. This delocalization (resonance) enhances the polarity of the O-H bond, making phenol more polar than standard aliphatic alcohols and imparting weakly acidic properties.
*Pentanol (C5H11OH)*
Pentanol is a moderately polar molecule with a net dipole moment similar to small alcohols around (1.6D to 1.7D).
Structure: It features a polar hydroxyl group (-OH) attached to a 5-carbon aliphatic chain (pentyl group).
"Dual" Nature: Pentanol has both a polar end and a nonpolar end. The (-OH) group allows it to engage in hydrogen bonding (making it somewhat soluble in water), while the relatively long 5-carbon nonpolar chain limits its solubility compared to smaller alcohols like methanol or ethanol.
*Highly soluble: (iii) formic acid, (iv) ethylene glycol* , because both are highly polar molecules.
*Formic Acid (HCOOH)*
Polarity: Highly polar.
Reason: It features a strongly polar carboxyl group (–COOH). The highly electronegative oxygen atoms pull electron density away from the carbon and hydrogen atoms.
Dipole Moment: The molecule has an asymmetrical, angular geometry. The uneven distribution of charge yields a distinct net dipole moment (approx 1.4 D).
Solubility: Because of its polarity, it can form strong hydrogen bonds and is infinitely miscible in other polar compunds.
*Ethylene Glycol (HOCH2CH2OH)*
Polarity: Highly polar.
Reason: Ethylene glycol contains two hydroxyl (–OH) groups that are highly polar because oxygen is significantly more electronegative than hydrogen.
Dipole Moment & Geometry: While the two (C–O) bond dipoles can cancel each other out when the molecule is drawn in a straight, fully extended (trans) configuration, this conformation is unstable. Instead, the molecule preferentially adopts a bent or "gauche" configuration due to internal hydrogen bonding. This rotation causes the molecule to have a permanent dipole moment, making it polar.
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