Question

Lab 6: Chemical Formula of Magnesium Oxide

Would the following experimental errors give a mass percent of magnesium too high or too low?

1. incomplete combustion of magnesium ["too low", "too high"]      
2. not heating the crucible to dryness ["too high", "too low"]      
3. spilled some ashes ["too high", "too low"]      

Answer 1

1) incomplete cumbustion of magnesium gives lower value for moles of magnesium from the formula moles = weight/molecular weight and hence leads to too low value.

2) not heating crucible to dryness will lead to lower value of mass of magnesium, also too low value.

3) spilled some ashes means lost weight of the magnesium, so again too low value.

all the three experimental errors mentioned will lead to reduction in magnesium weight, which lowers moles of magnesium and finally the mass percent of magnesium will be too low.