The question is: consider the double replacement, metathesisreaction: Potassium

Question

The question is: consider the double replacement, metathesisreaction:
Potassium Phosphate+ Magnesium sulfate (arrow)
(a) write the net ionic reaction.

I know that the ions will shift partners but I cant get the chargesbalanced right.

(b)If 100.0 mL of a 0.42 solution of Magnesium Sulfate are requiredto compeletly react with 77.2mL of Potassium Phosphate, What is theMolarity of the Potassium Phosphate Solution.

This seems like a limiting reagent problem so would I find theamount of moles then put mol/L?

Explanation / Answer

a)

2K3PO4 + 3MgSO4 = 3K2SO4 + Mg3(PO4)2

PO4 is insoluble, except with compounds of NH4+ and the alkalimetal cations (Group 1A)

Mg is not in Group 1A, so Mg3(PO4)2 is insoluble.

The ionic equation is:

6K + 2PO4 +3Mg + 3SO4 = 6K + 3SO4 + Mg3(PO4)2

Now, remove the ones that appear on both sides.

Cancel 6K, and 3SO4 from both sides

This leaves, 2PO4 +3Mg = Mg3(PO4)2

That is your net ionic equation. You shoud also show the ioncharges Mg is 2- and PO4 is 3+

b)

You want to use the equation:

Molarity1 X Volume 1 = Molarity2 X Volume2

(.42M)(.1L) = (M2)(.1 + .0772)

The Molarity of the Potassium Phosphate is.237M.

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