what are some factors that may cause a percent yield to be greater than 100% ? what are some that may cause it to be less?

Answer 1

more than 100 in a lab? Usually measurement errors.

Less than 100 percent? Measurement errors, some of the product is washed away in solution, or the reaction did not react the way one thought (I remember Mg burning in air, then measuring MgO to get yeild. Problem is, some of the Mg formed Mg3N2 with the air.