Molecular Mass of Methane

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Questions and Answers

What is the definition of one atomic mass unit (amu)?

One-twelfth the mass of a hydrogen atom

One-twelfth the mass of a helium atom

One-twelfth the mass of an oxygen atom

One-twelfth the mass of a carbon-12 atom (correct)

Why do atoms of different elements differ in mass?

Because they have different numbers of neutrons (correct)

Because they have different numbers of protons

Because they have different atomic numbers

Because they have different electron configurations

What occurs during a chemical reaction?

Atoms are created or destroyed

Electrons are transferred between atoms

Molecules are broken down into atoms

Atoms are rearranged to form new compounds (correct)

How is molecular mass calculated?

By adding the atomic masses of the elements present Signup and view all the answers

What is the mass of a hydrogen atom in amu?

1.6736 Signup and view all the answers

What is the standard atom used to define the atomic mass unit (amu)?

Carbon-12 Signup and view all the answers

Why do compounds have a fixed ratio of atoms?

Because compounds are formed when atoms of different elements combine in a fixed ratio Signup and view all the answers

What is the relationship between atomic mass and molecular mass?

Molecular mass is the sum of atomic masses Signup and view all the answers

What is the molar mass of sodium chloride?

58.5 g/mol Signup and view all the answers

How many atoms are in one mole of hydrogen?

6.022 × 10^23 atoms Signup and view all the answers

What is the defined value of one mole of a substance in terms of entities?

6.022 × 10^23 entities Signup and view all the answers

What is the relationship between the molar mass and molecular mass in units?

They are numerically equal. Signup and view all the answers

What is the correct molar mass of water?

18.02 g/mol Signup and view all the answers

In the SI system, how is the mole defined?

As the unit for the amount of substance. Signup and view all the answers

Which of the following statements is true about the mole concept?

The mole is similar to dozen or gross in counting. Signup and view all the answers

What is the total molecular mass when adding 72.066 u, 12.096 u, and 96.00 u?

180.162 u Signup and view all the answers

What is the molecular mass of methane (CH4)?

16.043 u Signup and view all the answers

Which term is used to describe the new unit for atomic mass?

u Signup and view all the answers

How is the average atomic mass calculated?

By considering the isotopes and their relative abundance Signup and view all the answers

What is the molecular mass of water (H2O) calculated as?

2(1.008 u) + 1(16.00 u) Signup and view all the answers

What type of substances do not contain discrete molecules as their constituent units?

Ionic compounds Signup and view all the answers

Which of these is NOT included in the calculation of average atomic mass?

Mass of the lightest isotope Signup and view all the answers

How is the mass of one oxygen atom in its isotope 16O represented?

15.995 amu Signup and view all the answers

What is the primary reason we calculate average atomic masses?

Due to the existence of multiple isotopes Signup and view all the answers

Study Notes

Molecular Mass

Methane (CH₄) molecular mass calculation: 1 carbon atom (12.011 u) + 4 hydrogen atoms (4 × 1.008 u) = 16.043 u.
Oxygen-16 (¹⁶O) atom mass is approximately 15.995 amu, corresponding to 16.00 u.
The unit 'amu' has been replaced by 'u' (unified mass).

Average Atomic Mass

Average atomic mass considers isotopes and their relative abundances in naturally occurring elements.
All atoms of a specific element have identical properties, including mass; isotopes differ in mass.
Example of a standard: the carbon-12 isotope (¹²C) is assigned exactly 12 amu.

Molecular Mass Calculation

Molecular mass is the sum of atomic masses of all elements in a molecule.
Determined by multiplying the atomic mass of each element by the number of its atoms and summing them.
Example: molecular mass of water (H₂O) is calculated as 2 (1.008 u) + 16.00 u = 18.02 u.

Mole Concept

The mole (symbol: mol) is the SI unit for the amount of substance.
One mole contains 6.022 × 10²³ entities (atoms, molecules, ions, etc.).
Molar mass numerically equals atomic/molecular/formula mass measured in grams per mole (g mol⁻¹).

Molar Mass Examples

Molar mass of water = 18.02 g mol⁻¹.
Molar mass of sodium chloride (NaCl) = 58.5 g mol⁻¹.

Percentage Composition

Previously focused on counting entities in a sample, moving towards calculating their percentage compositions within compounds.

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Description

Calculate the molecular mass of methane (CH4) containing one carbon and four hydrogen atoms.