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Old September 22nd, 2010, 12:02 PM   #1
excaliburr
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stoichiochemistry questions

concentrated tetrafluoroboric acid is 48% HBF_4 by mass. The density of the solution is 1.4g/mL. what volume is required to provide .127 moles of HBF_4?

do i have to find out the mass in moles of HBF_4 to start? if so how?

sorry im reeal new to this chemistry world. thanks!
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Old September 30th, 2010, 07:00 AM   #2
Unknown008
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First, you need to find the relative molecular mass of HBF_4

M_r = 1 + 80 + 19 + 19 + 19 + 19 = 157

So, 1 mol of HBF4 has a mass of 157 g
0.127 mol of HBF4 has a mass of = 157 x 0.127 = 19.9 g

Now, 1 mL of solution has a mass of 1.4 g.
Of that mass, 48% is HBF4. So, the mass of HBF4 = (48/100) x 1.4 = 0.672 g

So, 1 mL of solution contains 0.672 g of HBF4

Can you now find the volume which contains 19.9 g of HBF4?

Volume = (19.9 / 0.672) = 29.7 mL
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