What is the concentration of nitrate ions in 40.0 mL of a 0.25 M solution of copper(II) nitrate (Cu(NO_3)_2)?

• A. 0.25 M
• B. 0.50 M
• C. 0.75 M
• D. 0.125 M

Answer: (B)

Verified step by step guidance

1. Identify the chemical formula of copper(II) nitrate, which is Cu(NO\_3)\_2. This means each formula unit contains one copper ion (Cu\^{2+}) and two nitrate ions (NO\_3\^-).
2. Understand that the concentration of copper(II) nitrate given is 0.25 M, which means 0.25 moles of Cu(NO\_3)\_2 are dissolved per liter of solution.
3. Since each mole of Cu(NO\_3)\_2 produces 2 moles of nitrate ions, calculate the concentration of nitrate ions by multiplying the concentration of Cu(NO\_3)\_2 by 2: \(\text{[NO\_3\^-]} = 2 \times 0.25\,M\).
4. Note that the volume of the solution (40.0 mL) is not necessary to find the concentration of nitrate ions because molarity is independent of volume when the solution concentration is already given.
5. Conclude that the concentration of nitrate ions is twice the concentration of copper(II) nitrate, reflecting the stoichiometry of the compound.