achiver test 59 chem

[pistolpete007]

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What is the molality of 85% phosphoric acid, H3PO4, if the density of the solution is 1.70 g/ml?

A.1000 * (1.70/1) * (100.0 / 15.0) * (1.70/1) * (85.0 / 100.0) * (1/98) m
B.1000 * (1/1.70) * (100.0 / 15.0) * (1.70/1) * (85.0 / 100.0) * (1/98) m
i dont see why b is the answer?

 

[sl2obel2ts]

1.7g/ml is really unneccessary here u can figure it out without this info

molality = mole of H3PO4 / 1KG H2O
well lets say u got 1L
how many moles of H3PO4 u got?
1700g * 0.85/98

how much water u got in 1L?
1700 * 0.15

divide top by bottom
(0.85/98)/0.15
same as B

 

[pistolpete007]

1.7g/ml is really unneccessary here u can figure it out without this info

molality = mole of H3PO4 / 1KG H2O
well lets say u got 1L
how many moles of H3PO4 u got?
1700g * 0.85/98 where did u get 1700g from if u are leaving 1.7g/ml out

how much water u got in 1L?
1700 * 0.15 again same here...can u put units in these please? still kinda confused sorry lol

divide top by bottom
(0.85/98)/0.15
same as B

 

[sl2obel2ts]

doenst matter if u give it 1L or 1ml u dont even have to put 1700g. i jsut give the volume 1L, thus 1L * 1.7kg/1L = 1700g