Calculate how many grams of MgCl2 6H2O you need to take to prepare 500 g of a 20% MgCl2 solution.

Given:

mst = 500 g

v = 20%

To find:

m (MgCl2 * 6H2O) -?

Decision:

* v = (mst .. / mst.) * 100%

m thing. = v * mst. / 100%

m (MgCl2) = 20% * 500g / 100% = 100g – the mass of the required magnesium chloride in 500g of a 20% solution.

* Find out the mass fraction of magnesium chloride in the crystalline hydrate MgCl2 * 6H2O

M (MgCl2) = 95 g / mol

M (MgCl2 * 6H2O) = 95 + 6 * 18 = 203g / mol

v (MgCl2) = (95/203) * 100% = 46.8%

* The mass of the required crystalline hydrate is

m total = m number * 100% / v

m (MgCl2 * 6H2O) = 100g * 100% / 46.8% = 213.7g

Answer: 213.6 g. The mass of MgCl2 * 6H2O, necessary for the preparation of 500 g of a 20% solution of magnesium chloride.