Gravimetric Analysis- Questions

[dekoi]

Gravimetric Analysis-- Questions

I am in first-year Chemistry in university and I can't seem to find the answers for two questions from my course work. I have tried many times, and I keep reading the textbook but I still can't get it.

Please help if you know the correct answers. Thank you.

Here are the questions:

1.) A compound of Iron and Chlorine is soluble in water. An excess of Silver Nitrate was added to precipitate the chloride ion as silver chloride. If a 134.8 mg sample of the compound gave 304.8 mg of AgCl, what is the formula of the compound?

2.) Determine the oxidation number of HgCr2O7.

Thank you.

 

[dekoi]

Anyone?




...

 

[dekoi]

I would appreciate if anyone could give me suggestions on these questions.

 

[Cesium]

1) First figure out the mass of the chloride ions. The compound is FeCl_x.

304.8 mg AgCl --> 0.002 moles AgCl --> 0.002 moles Cl- --> 75 mg Cl-

134.8 mg FeCl_x - 75 mg Cl- = 59.4 mg Fe+x

0.002 moles Cl-
59.4 mg Fe+x --> 0.001 moles Fe+x

Therefore there is twice as much Cl- as Fe+x, so it must be Fe+2.

FeCl2

2)

Determine the oxidation number of HgCr2O7.

This does not make sense. The problem is asking you for the oxidation of a certain atom or for the oxidations numbers of each atom.

Since this is a compound you know that the overall charge is 0. The dichromate atom as an overall charge of -2. Oxygen is -2 in this case.

 

[cizie]

2) HgCr2O7

you will have to remember that Oxygen has an oxidation state of -2 no matter wat
so, O7= -2*7 = -14

as for Hg it will have an oxidation state of +2, because it is in the same group as zn.

therefore -14+2= -12

in closing Cr has an oxidation state of -12. but Cr2 will have to be -12/2 = -6. so since chromiun is beside oxygen its oxidation state changes to +6