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.

 

[DeeNos]

for providing a link to the question for clarification. Based on the information provided, the first step would be to calculate the moles of AgI produced. This can be done by dividing the mass of AgI (5.255 g) by its molar mass (234.77 g/mol). This gives a value of 0.0224 moles of AgI.

Next, we need to determine the moles of iodine in the compound. Since the only source of iodine in the reaction is from the compound, we can assume that the moles of iodine in the compound is the same as the moles of AgI produced. Therefore, the compound contains 0.0224 moles of iodine.

To determine the moles of cobalt in the compound, we need to use the mass of the compound (3.500 g) and the mass of iodine (0.0224 moles x 126.9 g/mol = 2.8426 g) to calculate the mass of cobalt. The mass of cobalt is 3.500 g - 2.8426 g = 0.6574 g. Converting this to moles using the molar mass of cobalt (58.93 g/mol) gives a value of 0.0112 moles of cobalt.

Finally, we can use the moles of iodine and cobalt to determine the empirical formula of the compound. The ratio of moles of iodine to moles of cobalt is approximately 2:1, giving an empirical formula of CoI2.