# MgO Lab: How would your calculated value for the percent composition of magnesium oxide been affected if all the magnesium in the crucible had not reacted?

## Calculation: % Mg = (m_(Mg))/m_(MgO) x 100% Will the %Mg be over-reported? Under-reported?

Jul 30, 2017

#### Answer:

Would it not be under-reported?

#### Explanation:

Look at your quotient.......

"%Metal" ="Mass of magnesium"/"Mass of magnesium oxide"xx100%......

Incomplete reaction DETRACTS from the denominator, and reduces the measured mass of magnesium oxide...., i.e. we measure $\text{mass of magnesium oxide + mass of unreacted metal}$. Since the starting mass of metal is UNCHANGED, the quotient should reduce...and %yield should be under-reported.....

Since magnesium oxidizes fairly fiercely, this circumstance is unlikely to occur.....of course, given the reaction some mass loss of the magnesium oxide ash could occur.

Here is a short video which summarizes this experiment.