GS-1 Physical Sciences Question 48

[michaelgar7090]

Isn't Mg3(PO4)2 insoluble? Solubility rules say phosphate compounds are insoluble, unless the cation is an alkali metal. Mg is not an alkali metal, it's an earth metal.

[nedaa.asba6809]

Yes, the Mg3(PO4)2 is insoluble but what we are focusing on In the question is the concentration of the Mg(+2) that can be obtained.

[Nirfoochil2984]

I found a way to do it all in one step.

(.005M Mg2+)(5mL) + (3x)(15mL) = (20mL)(.05M Mg2+)

x = molarity of Mg3(PO4)2 --> Solve for x

.025 + 45x = 1
45x = 0.975
x = 0.022

I put a 3 in front of x because there are 3 potential Mg2+ generated from each Mg3(PO4)2 in aqueous solution.

Converting everything to liters because molarity is in moles/ liters isn't necessary because you can cancel out mL by setting it up this way. Playing with all those zeros leaves more room for error in my opinion.

[dnpgr16513]

love it. saves so much time.