how many moles of hydroxide ions are there in 82.35 mL of a 2.164M Sr(OH)2 solution?

Question

i understand how to do the math for problems like these, but i don't know how to find the moles of just hydroxide ions.

Answer 1

So you know to do M x L = moles Sr(OH)2.
To find the OH^- alone, that is just twice the moles Sr(OH)2 BECAUSE there are two OH^- per mole Sr(OH)2. To find Sr alone, that is just 1 x (the same) as moles Sr(OH)2.
To find moles Mg in Mg3(PO4)2.
find moles Mg3(PO4)2, then double that to find PO4^-3, triple it to find Mg^+2, double to find moles P and multiply by 8 to find moles O. Got it??