Question

1. a 14.02 g sample of magnesium reacts with oxygen to form 24.98 g of magnesium oxide.

a. what is the experimental percent mass of magnesium in the sample?

b. if the formula for magnesium oxide is mgo, what is the expected percent mass of magnesium?

c. calculate the percent error.

\frac{|expected - experimental|}{expected} \times 100

Explanation:

Step1: Calculate experimental percent mass

Percent mass formula: $\frac{\text{mass of component}}{\text{mass of compound}}\times100$.
For part a, mass of magnesium ($\text{Mg}$) is $14.02$ g and mass of magnesium oxide ($\text{MgO}$) is $24.98$ g.
Experimental percent mass of $\text{Mg}=\frac{14.02}{24.98}\times100$.

Step2: Calculate expected percent mass

Molar mass of $\text{Mg}=24.31$ g/mol, molar mass of $\text{O}=16.00$ g/mol.
Molar mass of $\text{MgO}=24.31 + 16.00=40.31$ g/mol.
Expected percent mass of $\text{Mg}=\frac{24.31}{40.31}\times100$.

Step3: Calculate percent error

Let experimental value $E=\frac{14.02}{24.98}\times100\approx56.12\%$, expected value $Ex=\frac{24.31}{40.31}\times100\approx60.31\%$.
Percent error $=\frac{\vert Ex - E\vert}{Ex}\times100=\frac{\vert60.31 - 56.12\vert}{60.31}\times100$.

Answer:

a. $\frac{14.02}{24.98}\times100\approx56.12\%$
b. $\frac{24.31}{40.31}\times100\approx60.31\%$
c. $\frac{\vert60.31 - 56.12\vert}{60.31}\times100\approx6.95\%$