Molecular formula questions and Answers PDF

The molecular formula of a compound is a representation of the number and type of elements present in one molecular unit of the compound. This 10-question practice test deals with finding the molecular formula of chemical compounds.

A periodic table will be required to complete this test. Answers appear after the final question.

Question 1

An unknown compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen with a molecular mass of 60.0 g/mol. What is the molecular formula of the unknown compound?

Question 2

A hydrocarbon is a compound comprised of carbon and hydrogen atoms. An unknown hydrocarbon is found to contain 85.7% carbon and an atomic mass of 84.0 g/mol. What is its molecular formula?

Question 3

A piece of iron ore is found to contain a compound containing 72.3% iron and 27.7% oxygen with a molecular mass of 231.4 g/mol. What is the molecular formula of the compound?

Question 4

A compound containing 40.0% carbon, 5.7% hydrogen, and 53.3% oxygen has an atomic mass of 175 g/mol. What is the molecular formula?

Question 5

A compound contains 87.4% nitrogen and 12.6% hydrogen. If the molecular mass of the compound is 32.05 g/mol, what is the molecular formula?

Question 6

A compound with a molecular mass of 60.0 g/mol is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen. What is the molecular formula?

Question 7

A compound with molecular mass of 74.1 g/mol is found to contain 64.8% carbon, 13.5% hydrogen, and 21.7% oxygen. What is the molecular formula?

Question 8

A compound is found to contain 24.8% carbon, 2.0% hydrogen, and 73.2% chlorine with a molecular mass of 96.9 g/mol. What is the molecular formula?

Question 9

A compound contains 46.7% nitrogen and 53.3% oxygen. If the molecular mass of the compound is 60.0 g/mol, what is the molecular formula?

Question 10

A gas sample is found to contain 39.10% carbon, 7.67% hydrogen, 26.11% oxygen, 16.82% phosphorus, and 10.30% fluorine. If the molecular mass is 184.1 g/mol, what is the molecular formula?

Answers

1. C2H4O2
2. C6H12
3. Fe3O4
4. C6H12O6
5. N2H4
6. C2H4O2
7. C4H10O
8. C2H2Cl2
9. N2O2
10. C6H14O3PF

Cite this Article

Format

Your Citation

Helmenstine, Anne Marie, Ph.D. "Molecular Formula Practice Test Questions." ThoughtCo. https://www.thoughtco.com/molecular-formula-practice-test-questions-604125 (accessed November 30, 2022).

One of the easiest formulas for students to know and retain throughout tests or exams is the Chemical Formula of Magnesium Oxide. Before we get into the formula, let's have a look at the MgO compound name itself. Magnesium oxide, often known as magnesia, is a naturally occurring alkaline earth metal oxide that is mainly created by calcining certain minerals. At high temperatures, it is a solid that is both physically and chemically stable. As a result, it's usually employed in refractory materials.

MgO Compound Name

Magnesium oxide is formed up of the ions Mg2+ and O2-, which are joined by an ionic connection. However, based on the valency, we can conclude that the net charge in the molecules is zero and balanced, with one magnesium and one oxygen atom. As a result, the chemical formula for Magnesium Oxide is MgO.

Properties of Magnesium Oxide Formula 

Molecular formula of magnesium oxide- MgO

Molar Mass of magnesium oxygen symbol- 40.3044 g/mol

Density of magnesium oxygen formula- 3.58 g/cm3

Melting Point- 714 °C

Boiling Point- 1090°C

(Image will be uploaded soon)

(Image will be uploaded soon)

Experiment to Show Burning of Magnesium Ribbon Equation

When a piece of magnesium ribbon is ignited, it produces light and heat.

Aim:

This is a simple demonstration that explains the magnesium oxide symbol and the concept of an exothermic process and one that produces light energy.

Materials Required:

1. 6-8 cm magnesium ribbon sanded to remove oxide coating

2. Bunsen burner, charcoal grill lighter or similar

3. Tongs

Procedure: 

Adjust the flame to light blue after lighting the burner. Place the other end of the magnesium ribbon in the flame while holding one end with tongs. Holding the flaming ribbon at arm's length is recommended. Magnesium burns brightly and generates a lot of heat.

2Mg +  O2 → 2MgO (magnesium ribbon formula)

Magnesium oxidation or combustion in air has long been employed in photography and other photochemical reactions as a source of bright light. The energy released in this combustion is due to the reaction of magnesium with oxygen in the air, as shown in magnesium oxide balanced equation:

Magnesium oxide has a heat of formation of -601.83 kJ/mol. When magnesium burns, about 10% of the energy is converted to light, a figure that is unmatched among known energy transformations employed in the production of light.

Hazards:

The light from the burning magnesium ribbon is strong enough to inflict temporary blindness. Avoid gazing directly at the source of light. When magnesium is burned in the air, it produces a lot of heat, which can inflict burns and start a fire in flammable objects. A dry-powder extinguisher must be used because a carbon dioxide fire extinguisher will not extinguish burning magnesium.

Procedure for Balancing a Magnesium Oxide Equation:

To comprehend the stages needed in balancing a chemical equation, consider the chemical interaction between magnesium and oxygen.

Let's start by writing the reaction's word equation.

Magnesium + Oxygen → Magnesium oxide

Step 2: Write the chemical equation for the magnesium-oxygen reaction.

Mg + O2 → MgO

Step 3: Count how many times each element appears on both the LHS and RHS of this equation.

Mg +  O2 → MgO

Component  

Reactant 

Product

Magnesium

1

1

Oxygen        

2

1

This is an unbalanced magnesium oxide equation.

On each side of the equation, there are two oxygen atoms, but one magnesium atom on the reactants' side and two on the product's side. As a result, on the left-hand side, multiply the magnesium atom by two.

Component 

Reactant 

Product

Magnesium  

1 X 2 = 2

2

Oxygen    

2

2

The balanced equation is

2Mg +  O2 → 2MgO

The number of atoms in each reactant element equals the number of atoms in each product element.

Using the Arrow to write specific conditions The reaction takes place in the presence of heat.' When magnesium is heated, it reacts with oxygen in the air to generate magnesium oxide.

Different Types of Chemical Formulas

The chemical formula of a compound usually refers to its' molecular formula, which represents the total number of atoms of each component element in 1 molecule of the compound. The chemical compounds' compositions can be expressed in a variety of ways. 

A Chemical Formula can be expressed in a variety of ways, including:

• Empirical Formula- The ratio of the elements contained in a given chemical compound is represented by the empirical formula. The majority of empirical equations are derived through the study of experimental data. The molecular formulas can be used to derive empirical formulae.

• Molecular Formula-The number of components in a given molecule may be determined using the molecular formula. The elements are represented by their symbols in molecular formulas, and the number of atoms in each given element in the molecule is indicated with the subscript.

• Structural Formula- The structural formula of a given chemical compound supplies understanding into the configuration of the atoms in the given molecule.

Conclusion

Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium. MgO is prized as a refractory material that is physically and chemically stable at high temperatures.

What is a molecular formula answers?

What is molecular formula examples?

What are the 4 steps to calculating molecular formulas?