Advanced Placement (AP) Biology Practice Exam

What is the ionization constant for sodium chloride (NaCl)?

1. 1

2. 2

3. 3

4. 4

The correct answer is: 2

The ionization constant for sodium chloride (NaCl) is 2. This value reflects the number of ions produced when one formula unit of NaCl dissolves in water. When NaCl dissolves, it separates into two distinct ions: one sodium ion (Na⁺) and one chloride ion (Cl⁻). Therefore, the total number of ions formed from one mole of NaCl is two. The concept of ionization constant is particularly relevant in the context of solutions, where it's important to know how many ions a solute will produce upon dissociation. In contrast, the other choices do not accurately represent the number of ions produced. A value of 1 would indicate that there is only one ion involved, which does not apply to the dissociation of NaCl. Values of 3 and 4 are also incorrect because they would suggest that NaCl produces three or four separate ions upon ionization, which does not align with its chemical behavior in solution.