Calculate the molarity of Mg2+ ions in a diluted solution.

Question

Calculate the molarity (in mol/L) of the Mg²⁺ ion in a solution resulting from the dilution of 75.2 mL of 7.41×10^-3 M Mg(NO₂)₂ to a final volume of 346 mL.

Answer 1

First let's find how many actual moles of Mg2+ there are.

As the molarity is 7.41 x 10^-3 in Mg(NO)2, and it dissociates into Mg2+ and 2 (NO2)1- ions, the molarity of the Mg2+ is also 7.41 x 10^-3 M.

The number of moles of Mg2+ then 7.41 x 10^-3 moles/1000 mL x 75.2 mL = 5.57 x 10^-4 moles.

When this is diluted to 346 mL, there will be 5.57 x 10^-4 moles of Mg2+ in 346 mL.

By definition, molarity is moles per liter, so 5.57 x 10^-4 moles / 346 mL x 1000 mL/L = 1.61 x 10^-3 Molar

Always check the math.