A coordination compound is composed of 19.36% chromium, 31.69% NH3, 13.20% chlor
ID: 1070810 • Letter: A
Question
A coordination compound is composed of 19.36% chromium, 31.69% NH3, 13.20% chloride ion, and 35.76% sulfate ion (SO_4^2-), by mass, (a) Determine the empirical formula for the coordination compound in the form of Cr(NH_3)_xCl(SO_4) (where w, x, y, and z are simple integers) The solution of this compound does not yield any precipitate when treated with AgNO_3. However, when a solution that contains 1.450 g of the compound is treated with excess Ba(NO_3)_2, a white precipitate is formed. Upon filtering, washing, and drying, the precipitate yields 1.260 g of BaSO_4. (b) How many moles of sulfate ion (SO_4^2-) are present in the sample? Calculate the molar mass of the compound and determine its molecular formula, (c) Assuming that all of NH_3 are ligands, write the Werner's formula for this compound and give its systematic name.Explanation / Answer
First we will find the emperical formula of the coordination compound
Step 1 convert weight % to mole %
Mole % of Cr = 19.36 / 52 = 0.372
Mole % of NH3 = 31.69/17 = 1.864
Mole % of Cl- = 13.20/35.5 = 0.372
Mole % of SO4-2 = 35.76 / 96 = 0.372
Now making them in normal ratios we get : Cr : NH3 :Cl-:SO4-2 1:5:1:1
Therfor the emperical formula of the compound is Cr (NH3)5Cl-SO4
We know Cl- react with AgNO3 to give ppt whereas SO4-2 react with Ba(NO3)2 to give ppt of BaSO4 , So as we are getting ppt with BaCl2 ,It means SO4 is outside the cordination sphere.As the species which are in the cordination sphere cannot react individually.Hence the formula of the complex will be
[Cr(NH3)5Cl]SO4
b) Now weight of this compound = 52 + 17*5 +35.5 + 96 = 268.5
Moles of the coordinate compound present in 1.45 g = 1.45 / 268.5 =5.4 milli moles
Moles of BaSO4 formed = 1.260 /mass of BaSO4 = 1.260/233.43 = 5.4 milli moles
So we have same number of moles obtained , this means the SO4- are present in equal ratio . So no. of moles of SO4 in BaSO4 is 1 , so is in the coordinate compound.
Hence the required molecular formula of coordinate complex = [Cr(NH3)5Cl]SO4
Name will be pentaamminechlorochromium(III) sulfate