Question

4. An impatient student does not wait for all the iodine to react. Subsequently, the remaining iodine sublimes away during the product isolation step. Will the calculated mass ratio for the product, g I/g Zn, to be higher or lower than the correct value? Explain.

Answer 1

Answer:

Higher

Explanation:

It looks as if you prepared zinc iodide by the reaction of zinc with iodine.

Your procedure was probably something like this:

1. Measure out an exact amount of iodine and approximately the same mass if zinc (an excess).
2. React them in aqueous acetic acid.
3. Pour off the solution of zinc iodide and heat to dryness.
4. Determine the mass of the zinc iodide.

You know the mass of iodine used, so you can get the mass of zinc by difference.

For example, assume you measured out 0.5 g of I₂ and got 0.6 g of ZnI₂ as product. You would assume it contained 0.5 g of I₂ and 0.1 g of Zn. Your calculated mass ratio would be I₂/Zn = 5/1.

The impatient student loses 0.1 g of I₂ by sublimation, so they get only 0.55 g of ZnI₂. However, they still think it contains the original 0.5 g of I₂, and they determine the mass of Zn to be 0.05 g. Their calculated mass ratio is I₂/Zn = 0.5/0.05 = 10/1.

If some of the iodine sublimes away, the calculated value for the mass ratio will be higher than the correct value.