MCAT General Chemistry Question 190: Answer and Explanation

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Question: 190

1. Na₂SO₄ is soluble in water. If NaCl(s) is added to a solution of Na₂SO₄(aq) so that the concentration of Na⁺ doubles, then the:

A. PBr₃O
B. PF₅
C. CCl₄
D. SF₆

Correct Answer: A

Explanation:

A A bond has a dipole moment when the two atoms involved in the bond differ in electronegativity. However, an entire molecule can only have a dipole if it contains bond dipoles and is asymmetrical. Choice A is tetrahedral and not all four substituents are the same. Therefore, it is asymmetrical and has a small negative dipole in the direction of the most electronegative substituent, oxygen. The remaining choices are trigonal bipyramidal, tetrahedral, and octahedral respectively. All have identical substituents, are symmetrical, and have no net dipole moment.

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