Question

A 4.691 g sample of MgCl2 is dissolved in enough water to give 750. mL of solution. What is the magnesium ion concentration in this solution?

Answer 1

Convert 4.691 g MgCl2 to moles. moles = grams/molar mass.
There is 1 Mg ion/molecule MgCl2; therefore, moles Mg = moles MgCl2.
M Mg ion = moles/L = moles from above/0.750 = ??

Answer 2

6.52x10^-2

Answer 3

But when the MgCl2 is dissolved it will form MgO which is solid as well as HCl. So some if not all Of the Mg+ ions will have been used to form the MgO precipitate.