Question

In an experiment, a student dehydrated a hydrate unknown and found that the mass of hydrate was initially 4.13 g. After heating, the mass of the desiccant was 3.52 g.

a) calculate the mass % of water in the hydrate.

b)the possible hydrates that could be the unknown are

CuSO4-5H2O

BaCl2-2H2O

MgSO4-7H2O

Find the mass of salt(g), mass of water(g), and mass percent (%), of the possible hydrates.

c) Compare the mass % values to determine the identity of your unknown.

Answer 1

dm = mi - mf = 4.13-3.52 = 0.61 g of water

mol= mass/MW = 0.61/18 = 0.033888 mol of H2O

dissecant mol = masS/MW = 3.52 / MW

MW of CuSO4 = 159.609

MW of BaCl2= 208.23

MW of MgSO4= 120.366

If CuSO4

dissecant moles = 3.52 / MW = 3.52/159.609 = 0.022053.

If BaCl2

dissecant moles = 3.52 / MW = 3.52/208.23 = 0.016904

If BaCl2

dissecant moles = 3.52 / MW = 3.52/120.366 = 0.029244

find ratios:

0.033888 /0.022053= 1.53666

0.033888 /0.016904 = 2

0.033888 /0.029244= 1.1588

then, the only option is BaCl2 - 2 H2O

% mass = 3.52/4.13 * 100 = 85.23% of BaCl2