Your lab partner accidentally mixed some sodium chloride with your sample of Epsom salts (MgSO₄･7H₂O). You want to make a standard solution of magnesium ion, and this is the only sample of a magnesium salt you have. To determine the amount of magnesium salt in the mixture, you heat 100.00 g to drive off the water of hydration and find that the anhydrous mixture has a mass of 56.75 g. How many grams of the original salt mixture must you add to 1.000 L of water to make a 0.100 M solution of Mg²⁺ ion? g

Explanation:

Let x = the mass of MgSO₄·7H₂O

and y = the mass of NaCl

and z = the mass of MgSO₄

Then, you have two conditions:

That's two conditions but three unknowns. You need a third condition.

Fortunately, you are both an excellent chemist and mathematician. You know that

Mᵣ:          247.47             120.37

          MgSO₄·7H₂O ⟶ MgSO₄ + 7H₂O

m/g:             x                        z

This is your third condition.

1. Calculate the mass of MgSO₄

2. Calculate the moles of MgSO₄ needed for the solution

3. Calculate the mass of MgSO₄

4.Calculate the mass of the mixture required.

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