Question

As a solution of copper sulfate slowly evaporates, beautiful blue crystals made of Cu(II) and sulfate ions form such that water molecules are trapped inside the crystals. The overall formula of the compound is CuSO4 • 5H2O.

part 1

what is the percent water in this compound?

___%

part 2

at high tempreatures the water in the compound is driven off as steam. what mass percentage of the original sample of the blue solid is lost as a result?

___%

Answer 1

Atomic masses: Cu = 63.55 g/mol,
S = 32.07 g/mol
O x 4 = 16.00 g/mol x 4 = 64.00 g/mol
H = 1.008 g/mol,

So, H2O = (2*1.008+16.00)*5 = 90.10 g/mol

Molar mass of CuSO4,5H2O = 249.72 g/mol.

Out of that 249.72 grams, 90.10 grams is water,

So, percentage by mass of water in CuSO4,5H2O

= 90.10*100/249.72 = 36.08.%

SO 36.08% OF MASS IS LOST

AT HIGH TEMPERATURE ALL THE WATER MOLECULES ARE LOST SO

Calculate weight of the copper sulfate, CuSO4, without the water., Cu = 63.55 * 1 = 63.55 amu; S = 32.07 * 1 = 32.07 amu; and O = 16.00 * 4 = 64.00 amu. These values total 159.62 amu.

159.62 / 249.72 * 100 = 63.92 percent.

This means that a 100-gram sample of copper sulfate pentahydrate will contain 63.92 grams of copper sulfate. It also means that copper sulfate pentahydrate contains 100 - 63.92 = 36.08 percent water by mass.