Homework Question E9a

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Rebecca Chu 1C
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Joined: Fri Apr 06, 2018 11:02 am

Homework Question E9a

Postby Rebecca Chu 1C » Mon Apr 09, 2018 7:22 pm

"Epsom salts consist of magnesium sulfate heptahydrate. Write its formula. (a) How many atoms of oxygen are in 5.15 g of Epsom salts?"

I referred to the solutions manual while solving for the atoms of O. It used 11 mol O atoms in the dimensional analysis, but I'm confused why it isn't just 11 O atoms because I thought MgSO4·7H2O had 11 atoms of O not 11 moles of O atoms.

Please help. Thanks.

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Joined: Fri Apr 06, 2018 11:05 am

Re: Homework Question E9a

Postby nikitasridhar_1b » Mon Apr 09, 2018 8:46 pm

Since 6.022*10^23 is the number of particles (atoms, molecules, etc) in one mole, and since oxygen is repeated 11 times in the formula, we multiply the number of moles of oxygen by 6.02*10^23 to find the number of atoms in one mole. We multiplt 11 to this number since oxygen is repeated 11 times.

I have a diff q about E9; I don't get how they got the formula mass to be 246.48, I keep getting 239.477

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Joined: Thu Feb 15, 2018 3:00 am

Re: Homework Question E9a

Postby yazminedesan1F » Mon Apr 09, 2018 9:00 pm

Mg: 24.305 (atomic mass) x 1(amount of element)
S: 32.06 x 1 = 32.06
O: 16 x 4 = 64
for the 7H20 you bring 7 and multiply it by 2 for hydrogen to get 14 hydrogen and 7 multiplied by one oxygen is 7 oxygen
H: 1.008 x 14 = 14.112
O: 16 x 7=112
add all of these and you should get 246.477 which, because of sig figs, will be 246.48gmol^-1!

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