Predict which of the following compounds will be insoluble in water.
A. NaCl
B. HCl
C. CF4
D. CuSO4
The correct Answer and Explanation is:
The correct answer is C. CF4.
Explanation:
The solubility of a compound in water depends on the polarity of the compound and the ability of water molecules to interact with the compound’s molecules or ions. Water is a polar solvent, which means it has a positive and negative end due to the unequal sharing of electrons between oxygen and hydrogen atoms. Polar or ionic compounds generally dissolve well in water because they can form interactions with water molecules.
A. NaCl (Sodium Chloride)
NaCl is an ionic compound made up of sodium (Na⁺) and chloride (Cl⁻) ions. When NaCl is added to water, the polar water molecules surround the individual Na⁺ and Cl⁻ ions, effectively dissolving the salt. The positive end of the water molecule (the hydrogen atoms) is attracted to the negative chloride ions, while the negative end (the oxygen atom) is attracted to the positive sodium ions. This process is called dissociation, making NaCl soluble in water.
B. HCl (Hydrochloric Acid)
HCl is a polar covalent compound. When HCl is dissolved in water, it dissociates into hydrogen ions (H⁺) and chloride ions (Cl⁻), making it very soluble in water. HCl is also a strong acid, which means it dissociates completely in water, further enhancing its solubility.
C. CF4 (Carbon Tetrafluoride)
CF4 is a nonpolar molecule because the tetrahedral arrangement of fluorine atoms around the central carbon atom cancels out any dipole moments. Since water is polar and CF4 is nonpolar, there is no strong interaction between water molecules and CF4. Nonpolar molecules do not dissolve well in polar solvents like water due to the lack of attraction between the molecules, making CF4 insoluble in water.
D. CuSO4 (Copper(II) Sulfate)
CuSO4 is an ionic compound composed of copper (Cu²⁺) and sulfate (SO4²⁻) ions. Like NaCl, CuSO4 dissociates into its respective ions when dissolved in water. The polar water molecules are attracted to these ions, allowing the compound to dissolve. Therefore, CuSO4 is soluble in water.
In summary, CF4 is the correct answer because it is nonpolar, and nonpolar molecules do not dissolve well in water, which is polar.