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A 75.0g sample of liquid contains 17.5% by mass of H3PO4 (molar mass = 98.0g/mol). If

215.0mL of Ba(OH)2 is needed to completely neutralize the acid, determine the concentration
of the Ba(OH)2 solution used

2 answers

How much H3PO4 is in the sample?
That's 75.0 x 0.175 = approx 13g but you need to do it more accurately. How many mols is that? That's about 13/98 = approx 0.13.

2H3PO4 + 3Ba(OH)2 ==> Ba3(PO4)2 + 6H2O
mols Ba(OH)2 = approx 0.13 mols H3PO4 x (3 mol Ba(OH)2/2 mol H3PO4) = about 0.13 x 3/2 = about 0.2 mols Ba(OH)2.
So M Ba(OH)2 = mols/L. YOu have mols and convert 215.0 mL to L.
Donloud