Question

how many grams mg are in 1000 ml ( mgcl2.6h2o disolved in deionized water)

Answer 1

When the compound is dissolved it breaks into $Mg^{2+}, Cl^-$ ions.

Let Molarity of the compound be x M.

Then molarity of the ions is as follows : $Mg^{2+}=x M, Cl^-=2x M$

Thus, amount of Mg present in 1000 ml is $24x$ gms. (since, atomic weight of Magnesium is 24 gm.)