Which molecule would you expect to be more soluble in water, CCl4 or CH2Cl2?
The correct answer and explanation is:
Correct Answer: CH₂Cl₂ (dichloromethane) is more soluble in water than CCl₄ (carbon tetrachloride).
Explanation:
Water is a polar solvent, meaning it dissolves other polar substances more readily than nonpolar ones. This principle is often summarized as “like dissolves like.” When evaluating the solubility of two molecules in water, their polarity becomes the main factor to consider.
CH₂Cl₂ (dichloromethane) has a bent molecular shape and contains two chlorine atoms and two hydrogen atoms bonded to a central carbon. Because chlorine is significantly more electronegative than hydrogen, the C–Cl bonds create dipoles. Due to the geometry of the molecule, these dipoles do not cancel out. This makes CH₂Cl₂ a polar molecule. Polar molecules interact more favorably with the polar water molecules through dipole-dipole interactions and hydrogen bonding with water, increasing solubility.
On the other hand, CCl₄ (carbon tetrachloride) is a symmetrical molecule with four chlorine atoms evenly distributed around a central carbon atom. Although each C–Cl bond is polar, the molecule’s tetrahedral symmetry means that the individual bond dipoles cancel each other out. As a result, CCl₄ is a nonpolar molecule. Nonpolar molecules do not interact well with water molecules because they cannot form strong dipole-dipole attractions or hydrogen bonds. This leads to very low solubility in water.
In summary, the polarity of CH₂Cl₂ allows it to dissolve better in water than nonpolar CCl₄. While both are covalent compounds, the key difference lies in molecular shape and the presence of net dipole moments. CH₂Cl₂’s polar nature allows it to interact favorably with water, while CCl₄’s nonpolar character results in poor solubility.