Q: Which calculation is necessary to determine the number of moles of magnesium used in the experiment?

$\text{moles of Mg} = \dfrac{\text{mass of Mg}}{24.31}$

Question 1

In the Magnesium Oxide Lab, which of the following is the correct empirical formula for magnesium oxide based on the experimental data and calculations?

Accepted Answer

$\mathrm{MgO}$

Question 2

During the experiment, why is it important to record the mass of the crucible and lid before and after the reaction?

Accepted Answer

To determine the mass of magnesium and oxygen that reacted by subtracting the mass of the crucible and lid from the total mass.

Question 3

If the mass of magnesium used is $0.06\ \mathrm{g}$ and the mass of oxygen gained is $0.04\ \mathrm{g}$, what is the mole ratio of magnesium to oxygen? (Atomic masses: Mg = $24.31\ \mathrm{g/mol}$, O = $16.00\ \mathrm{g/mol}$)

Accepted Answer

$\dfrac{0.06/24.31}{0.04/16.00} \approx 1:1$

Question 4

A student finds the mass of magnesium after burning is lower than expected. Which error most likely occurred?

Accepted Answer

Some magnesium oxide escaped through the opening in the lid.

Question 5

Why does the experimental mole ratio of Mg to O sometimes appear higher than the theoretical value?

Accepted Answer

Loss of magnesium oxide product during heating causes the calculated oxygen mass to be artificially high.

Question 6

Given the following data: mass of crucible and lid = $23.75\ \mathrm{g}$, mass of crucible, lid, and magnesium before heating = $23.81\ \mathrm{g}$, mass after reaction = $23.87\ \mathrm{g}$, calculate the mass of oxygen that reacted.

Accepted Answer

$0.07\ \mathrm{g}$

Question 7

If a student calculates the empirical formula of magnesium oxide as $\mathrm{MgO_2}$, which experimental error most likely occurred?

Accepted Answer

The mass of oxygen was overestimated due to contamination or loss of magnesium oxide.

Question 8

Which calculation is necessary to determine the number of moles of magnesium used in the experiment?

Accepted Answer

$	ext{moles of Mg} = \dfrac{	ext{mass of Mg}}{24.31}$

Question 9

After burning magnesium in air, a student finds the mass of the product is less than expected. What is the most likely cause?

Accepted Answer

Some magnesium oxide escaped from the crucible during heating.

Question 10

If the calculated mole ratio of Mg to O is $3.95:1$, what should the student do to determine the correct empirical formula?

Accepted Answer

Divide both values by the smallest number to get a ratio close to $1:1$.

Question 11

Which of the following best explains why the mass of oxygen might be too high in the experiment?

Accepted Answer

Magnesium oxide product escaped, causing the oxygen mass to be overestimated.

Question 12

A student records the following: mass of Mg = $0.06\ \mathrm{g}$, mass of O = $0.04\ \mathrm{g}$. Calculate the empirical formula for magnesium oxide.

Accepted Answer

$\mathrm{MgO}$

Question 13

Why is it necessary to burn magnesium in a crucible with a lid during the experiment?

Accepted Answer

To prevent magnesium oxide from escaping and to control the amount of oxygen entering.

Question 14

If the mass of magnesium used is $0.06\ \mathrm{g}$ and the mass of oxygen gained is $0.07\ \mathrm{g}$, what is the empirical formula of the product? (Mg = $24.31\ \mathrm{g/mol}$, O = $16.00\ \mathrm{g/mol}$)

Accepted Answer

$\mathrm{Mg_2O_3}$

Question 15

Which step is NOT part of the procedure for determining the empirical formula of magnesium oxide?

Accepted Answer

Measuring the temperature of the crucible before and after reaction.

Question 16

If a student does not use a lid during the heating of magnesium, what is the most likely consequence?

Accepted Answer

Magnesium oxide will escape, leading to inaccurate mass measurements.

Question 17

What is the purpose of calculating the number of moles of magnesium and oxygen in the experiment?

Accepted Answer

To determine the simplest whole number ratio and thus the empirical formula.

Question 18

If the mass of oxygen calculated is less than expected, what is the most likely explanation?

Accepted Answer

Not all of the magnesium reacted, so the oxygen mass is lower than it should be.

Question 19

Which of the following is a possible source of error that could lead to a calculated empirical formula of $\mathrm{Mg_3O_2}$?

Accepted Answer

Loss of magnesium oxide product during heating.

Magnesium Oxide Lab Notes

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