Which pair is immiscible?

Which pair is immiscible?

• A. Water and Ethanol
• B. Water and Gas
• C. Salt in Water
• D. Oil and Water

Answer: (D)

Immiscibility arises when two liquids do not mix to form a single phase because their molecular interactions are so different that favorable interactions between them are negligible. Water is highly polar and forms strong hydrogen bonds with itself, while most oils are nonpolar hydrocarbons that cannot engage in hydrogen bonding with water. Mixing would require breaking water–water hydrogen bonds and creating new, weak oil–water interactions, which is energetically unfavorable, so the liquids separate into distinct layers. Oil and water are the classic example of this, with the oil usually floating on top due to its generally lower density. In contrast, water and ethanol mix readily because ethanol can also engage in hydrogen bonding and shares similar polarity; salt in water dissolves to form a homogeneous solution (not two layers); and water and gas do not form two liquid phases—gases dissolve to some extent rather than creating an immiscible pair.

Immiscibility arises when two liquids do not mix to form a single phase because their molecular interactions are so different that favorable interactions between them are negligible. Water is highly polar and forms strong hydrogen bonds with itself, while most oils are nonpolar hydrocarbons that cannot engage in hydrogen bonding with water. Mixing would require breaking water–water hydrogen bonds and creating new, weak oil–water interactions, which is energetically unfavorable, so the liquids separate into distinct layers. Oil and water are the classic example of this, with the oil usually floating on top due to its generally lower density. In contrast, water and ethanol mix readily because ethanol can also engage in hydrogen bonding and shares similar polarity; salt in water dissolves to form a homogeneous solution (not two layers); and water and gas do not form two liquid phases—gases dissolve to some extent rather than creating an immiscible pair.