What is the molar concentration of sulfate ions (SO_4^{2-}) in a 0.150 M Na_2SO_4 solution?

• A. 0.050 M
• B. 0.075 M
• C. 0.150 M
• D. 0.300 M

Answer: (C)

Verified step by step guidance

1. Identify the chemical formula of the compound: sodium sulfate is Na_2SO_4, which dissociates completely in water into 2 Na^+ ions and 1 SO_4^{2-} ion per formula unit.
2. Write the dissociation equation: \(\text{Na}_2\text{SO}_4 \rightarrow 2\text{Na}^+ + \text{SO}_4^{2-}\).
3. Recognize that for every 1 mole of Na_2SO_4 dissolved, 1 mole of SO_4^{2-} ions is produced because the ratio of Na_2SO_4 to SO_4^{2-} is 1:1.
4. Since the initial concentration of Na_2SO_4 is 0.150 M, the concentration of sulfate ions will be the same, 0.150 M, due to the 1:1 molar ratio.
5. Therefore, the molar concentration of sulfate ions in the solution is equal to the molar concentration of the sodium sulfate solution.