A six-coordinate complex of formula CrCl6.6H2O is green in colour. A 0.1M solution of the complex when treated with excess of AgNO3 gave 28.7g of white precipitate. The formula of the complex would be:
A
[Cr(H2O)6]Cl3
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B
[Cr(H2O)5Cl]Cl2.H2O
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C
[Cr(H2O)4Cl2]Cl.2H2O
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D
[Cr(H2O)3Cl3].3H2O
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Solution
The correct option is B[Cr(H2O)5Cl]Cl2.H2O Let us call the six-coordinate compound of Cr 'x'. When a 0.1 M solution of x is treated with excess AgNO3, we get white precipitate of AgCl. The number of moles of AgCl found will give us an estimate of the number of moles of Cl outside the coordination sphere in x.
We know that the molecular weight of AgCl is 143 g.
Obtained weight of precipitate is 28.7 g.
Hence, the number of moles of AgCl will be 28.7/1430.1= 2 mol
Hence, we know that 2 moles of Cl atoms are present outside the coordination sphere in the solution. This tells us that the formula of the six coordination compound has to be [Cr(H2O)5Cl]Cl2.H2O