1990 AP chem question

[Lyristes]

An experiment is performed to determine the empirical formula of a copper iodide formed by direct combination of elements. A clean strip of copper metal is weighed accurately. It is suspended in a test tube containing iodine vapor generated by heating solid iodine, A white compound forms on the strip of copper, coating it uniformly. The strip with the adhering compound is weighed. Finally, the compound is washed completely from the surface of the metal and the clean strip is dried and reweighed.

Mass of clean copper strip: 1.2789 g
Mass of copper strip and compound: 1.2874 g
Mass of copper strip after washing: 1.2748 g

a. The number of moles of iodine that reacted?
a. The number of moles of copper that reacted?
b. Explain how you would determine the empirical formula for the copper iodide.?

c. Explain how each of the following would affect the empirical formula that could be calculated.
(1) Some unreacted iodine condensed on the strip.
(2) A small amount of the white compound flaked off before weighing.

For the moles of I and Cu reacted, I got: 6.698 * 10^-5 mol I and 1.983 * 10^-4 mol Cu, leading to the empirical formula CuI₃. What did I do wrong????

[ChenBeier]

Mass of copper strip and compound: 1.2874 g - Mass of clean copper strip: 1.2789 g = mass of iodine as 0.5 I₂
Mass of clean copper strip: 1.2789 g - Mass of copper strip after washing: 1.2748 g = mass of Cu

Calculate moles by n = m/M

Your copper value is wrong.

[pugdistant]

It's easy to undertand!