S1.4.3 Molar mass

Summary

This video script by MSJ Chem explores the concept of molar mass, defining it as the mass in grams of one mole of a substance, measured in grams per mole. It distinguishes between molar mass and relative atomic mass, noting that while they are numerically equal, molar mass includes the unit grams per mole. The script demonstrates the conversion from relative atomic mass to molar mass using the molar mass constant and illustrates the process with examples of various substances, including ethanol, emphasizing the importance of units in molar mass calculations.

Takeaways

• 🔍 Molar mass is defined as the mass in grams of one mole of a substance, with the unit grams per mole.
• 📏 The molar mass of a substance is numerically equal to its relative atomic mass but has units, unlike the dimensionless relative atomic mass.
• 📚 Relative atomic masses of elements can be found on the periodic table and are used to calculate molar mass.
• 🔢 To convert from relative atomic mass to molar mass, multiply by the molar mass constant, approximately one gram per mole.
• 🌐 The molar mass of elements like carbon, magnesium, sulfur, and iron are 12.01 g/mol, 24.31 g/mol, 32.07 g/mol, and 55.85 g/mol respectively.
• 🧪 Calculating the molar mass of a compound involves summing the molar masses of its constituent atoms and then multiplying by the molar mass constant.
• 🍺 For example, the molar mass of ethanol (C2H5OH) is calculated by adding the molar masses of 2 carbon atoms, 6 hydrogen atoms, and 1 oxygen atom, resulting in 46.08 g/mol.
• 🌀 The molar mass of a molecule or compound tells us the mass of one mole of that substance, such as 46.08 grams for one mole of ethanol.
• 📘 The script provides examples of various substances, including molecular oxygen (O2), water (H2O), methane (CH4), sodium chloride (NaCl), ammonium carbonate, and aluminum oxide, with their respective molar masses.
• ⚖️ The relative molecular mass or relative formula mass of a compound is numerically equal to its molar mass, but the former lacks units while the latter is expressed in grams per mole.

Q & A

What is the definition of molar mass?

Molar mass is the mass in grams of one mole of a substance, with the unit being grams per mole.

What is the relationship between molar mass and the number of particles in a mole?

One mole of any substance contains 6.02 times 10 to the 23 particles, and the molar mass numerically equals the relative atomic mass of the substance.

Where can the relative atomic masses of elements be found?

The relative atomic masses of elements can be found on the periodic table.

How is molar mass different from relative atomic mass?

While molar mass and relative atomic mass are numerically equal, the difference is that molar mass has units of grams per mole, whereas relative atomic mass is dimensionless and has no units.

What is the molar mass constant and what is its approximate value?

The molar mass constant is used to convert from relative atomic mass to molar mass, and it is approximately equal to one gram per mole.

What is the molar mass of carbon, and how is it determined?

The molar mass of carbon is 12.01 grams per mole, which is determined by multiplying its relative atomic mass of 12.01 by the molar mass constant.

How do you calculate the molar mass of a compound like ethanol?

To calculate the molar mass of a compound, you sum the molar masses of all the atoms in the molecule. For ethanol (C2H5OH), it's calculated as 2 times the molar mass of carbon (2 * 12.01) plus the molar mass of oxygen (16) plus 6 times the molar mass of hydrogen (6 * 1.01).

What is the molar mass of ethanol and how is it derived?

The molar mass of ethanol is 46.08 grams per mole, derived from the sum of the relative atomic masses of its constituent atoms multiplied by the molar mass constant.

Can you provide an example of calculating the molar mass of a diatomic molecule like O2?

The molar mass of O2 is 32.00 grams per mole, which is twice the relative atomic mass of a single oxygen atom (16 * 2).

How does the molar mass of water (H2O) compare to its relative molecular mass?

The molar mass of water is 18.02 grams per mole, which is numerically equal to its relative molecular mass (2 * 1.01 for hydrogen + 16 for oxygen).

What is the molar mass of sodium chloride (NaCl), and how is it calculated?

The molar mass of sodium chloride is 58.44 grams per mole, calculated by adding the molar masses of sodium (22.99) and chlorine (35.45).

Why does the molar mass of a compound have units, while the relative formula mass does not?

The molar mass has units of grams per mole because it represents the mass of one mole of the substance. The relative formula mass does not have units because it is a dimensionless ratio comparing the mass of atoms to the mass of carbon-12.