some chemistry problems....help, pls...?

Question

i have some problems here about chem and i have a hard time recalling how to answer these..
anyways, i have my own answers to these but im not really sure if i got the right answers.

please help me try these out..
:)

1.a standard sol'n to be used for UV-Vis analysis is prepared by dissolving 0.0702 g of reagent grade Fe(NH4)2(SO4)2 .6H2O in water to a volume of 1L. What is the conc'n in ppm Fe??

2. What is the molarity of K+ in an aqueous sol'n that contains 63.5 ppm of K3Fe(CN)6??

3. describe the preparation of 2L of 0.108 M BaCl2 from BaCl2.2H2O.

Answer 1

ppm and ppb are somewhat loosely defined, since ppm may mean ppm in weight/mass, ppm in volume, ppm in atoms, or even in mass/volume.
In your written content, it seems to me that the ppm is in mass/volume.

1) The molar mass of Fe(NH4)2(SO4)2•6H2O is 392.14g/mol
The molar mass of Fe is: 55.845 g/mol.
Hence 0.0702g Fe(NH4)2(SO4)2 .6H2O contains:
(55.845/392.14)*0.0702g Fe or 0.01g Fe.
Thus the solution is of 10 ppm Fe (since 1L ≈ 1kg).

2) Notice that the molar mass of Potassium ferricyanide is: 329.24 g/mol.
63.5 ppm of K3Fe(CN)6 in 1L <==> 0.0635g of K3Fe(CN)6 in 1L <==> 0.000193 M K3Fe(CN)6 = 0.193 mM K3Fe(CN)6.

3) The molar mass of BaCl2.2H2O is: 208.2324 g/mol.
2L of 0.108 M BaCl2 contains 0.216 mole of BaCl ==> 44.978g BaCl2.2H2O.
Weigh 44.978g BaCl2.2H2O, transfer to a 2L cylindrical measure, rinse the weighing glass a few times and pour the rinsing water also into the cylindrical measure. dissolve all the solid, and add water to the mark of 2L.