## Fraction of total mass due to oxygen?

Jessica Pham_4B
Posts: 9
Joined: Wed Nov 15, 2017 3:00 am

### Fraction of total mass due to oxygen?

E.29 A chemist measured out 8.61 g of copper(II) chloride tetrahydrate, CuCl2 4H2O.
(a) How many moles of CuCl2 4H2O were measured out? 0.0417 mol
(b) How many moles of Cl ions are present in the sample? .0834 mol
(c) How many H2O molecules are present in the sample?
(d) What fraction of the total mass of the sample was due to oxygen?

Does anyone know how to approach part (d). I'm having a hard time understanding what the question is and how to approach it. Thank you <3

Chris Freking 2G
Posts: 60
Joined: Fri Sep 28, 2018 12:29 am

### Re: Fraction of total mass due to oxygen?

To clear up any confusion, it's referring to the oxygen itself, not oxygen gas molecules.

To find the fraction of the total mass of the sample due to oxygen, divide the molar mass of the oxygen by the molar mass of the entire compound.

(4 * 15.999 g mol^-1) / (206.53 g mol^-1)
(The 4 comes from the amount of oxygen moles in the compound, the 15.999g mol ^-1 comes from the atomic mass of oxygen, and the 206.53 g mol^-1 comes from the added atomic weight of the entire compound)

= 0.3099 or 30.99%