Gravimetric Analysis with empirical formula

[asz304]

Homework Statement

a 3.500 g sample of a compound of cobalt and iodine was dissolved in water and treated with excess AgNO3 solution producing 5.255g AgI. Determine the empirical formula.

A clearer view of the question:http://www.chem.mun.ca/courseinfo/c1050/Louise_Dawe/Basic%20Chemical%20Concepts%20I.pdf"

question # 20.

The Attempt at a Solution

I started by getting the mole of AgI and making a mole to mole ratio with Co_xI_y...and I'm not sure if what I did was right.
Thanks

 

[symbolipoint]

You do not yet know the mole ratios or atom ratios of the I to the Co. First use the 1:1 mole ratio for the reaction of AgNO3 to the Iodide ion. How many moles of Iodide were precipitated? That gives you the number of moles of I from the sample of the cobalt-iodine compound. Convert to grams; find the grams of cobalt by difference, since you know how much sample you used.

 

[asz304]

Do I need to find the moles of AgNO3 to find the 1:1 mole ratio? or get the moles of AgI from it's mass 5.255g? and to which Iodide are you referring to?

Thanks

 

[Borek]

AgNO₃ was in excess to ensure all iodine has been precipitated as AgI (silver iodide). Exact amount of AgNO₃ doesn't matter.