3.34 Answers Calculate The Molar Mass of The Following Substances

What is molar mass?

Molar mass, also known as molecular weight, is the mass of one mole of a substance. It's a crucial concept in chemistry because it allows chemists to relate the mass of a substance to the amount of substance (measured in moles). The molar mass is typically expressed in grams per mole (g/mol).

The mole is the SI unit for amount of substance, defined as exactly 6.02214076 × 10²³ particles (atoms, molecules, ions, or electrons). This number is known as Avogadro's number. When we talk about molar mass, we're essentially referring to the mass of Avogadro's number of particles.

How to calculate molar mass

Calculating molar mass involves summing the atomic masses of all atoms in a molecule. Here's a step-by-step guide:

1. Identify the chemical formula of the substance.
2. Determine the atomic mass of each element in the formula from the periodic table.
3. Count the number of atoms of each element in the molecule.
4. Multiply the atomic mass of each element by the number of atoms of that element.
5. Sum all these values to get the molar mass.

For example, to calculate the molar mass of water (H₂O):

1. Hydrogen (H) has an atomic mass of approximately 1.008 g/mol.
2. Oxygen (O) has an atomic mass of approximately 15.999 g/mol.
3. There are 2 hydrogen atoms and 1 oxygen atom in water.
4. Molar mass of water = (2 × 1.008) + (1 × 15.999) = 18.015 g/mol.

Examples of molar mass calculations

Let's look at a few examples to illustrate how to calculate molar mass:

Example 1: Methane (CH₄)

Methane is the main component of natural gas. To calculate its molar mass:

1. Carbon (C) has an atomic mass of approximately 12.011 g/mol.
2. Hydrogen (H) has an atomic mass of approximately 1.008 g/mol.
3. There is 1 carbon atom and 4 hydrogen atoms in methane.
4. Molar mass of methane = (1 × 12.011) + (4 × 1.008) = 16.043 g/mol.

Example 2: Ethanol (C₂H₅OH)

Ethanol is a common alcohol used in beverages and as a solvent. To calculate its molar mass:

1. Carbon (C) has an atomic mass of approximately 12.011 g/mol.
2. Hydrogen (H) has an atomic mass of approximately 1.008 g/mol.
3. Oxygen (O) has an atomic mass of approximately 15.999 g/mol.
4. There are 2 carbon atoms, 6 hydrogen atoms, and 1 oxygen atom in ethanol.
5. Molar mass of ethanol = (2 × 12.011) + (6 × 1.008) + (1 × 15.999) = 46.069 g/mol.

Example 3: Sodium Chloride (NaCl)

Sodium chloride is table salt. To calculate its molar mass:

1. Sodium (Na) has an atomic mass of approximately 22.990 g/mol.
2. Chlorine (Cl) has an atomic mass of approximately 35.453 g/mol.
3. There is 1 sodium atom and 1 chlorine atom in sodium chloride.
4. Molar mass of sodium chloride = (1 × 22.990) + (1 × 35.453) = 58.443 g/mol.

Molar masses of common substances

Here's a table showing the molar masses of some common substances: