# chemistry

posted by on .

Balance each of the following redox equations using the half-reaction method.

HI(s) + H2SO4 (aq) --> H2S(g) + I2 (s)

My only question about this equation is...how do I know how many electrons I need to put on both sides? Other than that I know how to do it.

• chemistry - ,

I in HI has an oxidation state of -1. On the other side I2 is zero. So in going from 2I^- to I2, I lost 2electrons.
S in H2SO4 is +6. S in H2S is -2. In going from +6 to -2, there is a gain of 8 electrons. I do this intuitively but you can do it mathematically.
+6-(-2) = +8 so gain of 8.
-2-(0) = -2 so loss of 2.

• chemistry - ,

You carefully measure 20.00 of powder and add it to 81.00 of solution in a reaction flask of known mass. You notice bubbles as a reaction takes place. You then determine that the contents of the flask have a mass of 92.80 . The relevant equation is

Assuming no other reactions take place, what mass of was produced in this reaction?
Express the mass numerically in