## Question E29

Jane Burgan 1C
Posts: 73
Joined: Fri Sep 28, 2018 12:15 am

### Question E29

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

How do you figure out b and c?

Christopher Tran 1J
Posts: 77
Joined: Fri Sep 28, 2018 12:15 am

### Re: Question E29

For Part B and C, you need the number of moles of CuCl2 * 4H2O calculated in Part A, which is 0.0417 mol CuCl2*4H2O.

Part B: For each mole of CuCl2*4H2O, there are two moles of Cl- because of the subscript number 2 in CuCl2. Therefore, multiply 0.0417 by 2 to get 0.0834 mol Cl- ions.

Part C: For each mole of CuCl2*4H2O, there are four moles of H2O because of the coefficient 4 before H2O. Therefore, multiply 0.0417 by 4 to get 0.1668 mol H2O.

For each mol of H2O, there are 6.022*10^23 molecules of H2O (Avogadro's number), so you have to multiply 0.1668 mol by 6.022*10^23 to get 1.00*10^23 molecules H2O.