10 mL of 0.2 M NiSO4 is mixed with 20 mL of 0.1 M CuSO4. Calculate the molarity of Ni2+, Cu2+and SO42- ions present in solution.

Question

10 mL of 0.2 M NiSO4 is mixed with 20 mL of 0.1 M CuSO4. Calculate the molarity of Ni2+, Cu2+and SO42- ions present in solution.

Answer 1

Final volume = 10 ml + 20 ml = 30 ml

Ni²⁺ comes only from NiSO₄

Cu²⁺ comes only from CuSO₄

SO₄^2- comes from BOTH NiSO₄ and CuSO₄

Find moles of each ion as follows:

moles Ni2+ and SO42- from NiSO4 = 0.01 L x 0.2 moles/L = 0.002 moles Ni2+ and 0.002 moles SO42-

moles Cu²⁺ and SO₄^2- from CuSO₄ = 0.02 L x 0.1 moles/L = 0.002 moles Cu²⁺ and 0.002 moles SO₄^2-

Total moles of SO₄^2- = 0.002 + 0.002 = 0.004 moles SO₄^2-

Molarity of each ion (to 1 significant figure):

Ni²⁺ = 0.002 moles/0.03 L = 0.0666 M = 0.07 M

Cu²⁺ = 0.002 moles/0.03 L = 0.0666 M = 0.07 M

SO₄^2- = 0.004 moles SO42-/0.03 L = 0.133 M = 0.1 M