Question

Question #729cf

Answer 1

576g

Explanation:

Al2(SO4)3 has 3 x 4 = 12 oxygen atoms

that weigh 16g/m apiece. Therefore

3mole x 16g/mole x 12 = 576g

= the mass of oxygen contained in 3moles Aluminum Sulfate.

Answer 2

`1.68` grams O.

Explanation:

First, calculate the number of moles of `Al_2(SO_4)_3` in 3.0 moles. Then multiply by 12 to get the total number of `O` moles (or we can us 6 for `O_2` - just don't get them confused). Finally, multiply this by the molecular weight of O to get the final value in grams.

`Al_2(SO_4)_3` = `342 g/"mol"`

`3.0/342 = 0.00877` moles `Al_2(SO_4)_3`

`0.00877 xx 12 = 0.105` moles O
`0.105 xx 16 = 1.68` grams O

CHECK:
Mass% O in `Al_2(SO_4)_3`: `192/342 = 56.14%`
`0.5614 xx 3.0 = 1.68` Correct.

(OR, do the check and calculation in the reverse order, if you like.)