[helpme]

If I want a .2 Molar concentration of MgCl2 in 3 Liters how many grams of MgCl2 should I add?

[chemicalLindsay]

allright one mole of MgCl2 is 94 grams (hence magnesium 24g and two times chlorine 70g).now if we were to make a 0.2 molar solution in one litre of solution we would add a fifth of a mole of MgCl2 which equates to roughly 18.8 grams of MgCl2 and 981.2g of water.To increase this to 3 liters we simply times it by three to get 56.4g of MgCl2 and 2943.6g of water.
does that answer your questionand good luck.

[Scratch-]

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[jdurg]

allright one mole of MgCl2 is 94 grams (hence magnesium 24g and two times chlorine 70g).now if we were to make a 0.2 molar solution in one litre of solution we would add a fifth of a mole of MgCl2 which equates to roughly 18.8 grams of MgCl2 and 981.2g of water.To increase this to 3 liters we simply times it by three to get 56.4g of MgCl2 and 2943.6g of water.
does that answer your questionand good luck.

The concentration is in Molar, not Molal so the mass of the water should not even be considered in all of this.  It's the total volume of solution that is important.