Introduction to Moles

Introduction to Moles

• Moles are a unit of measurement used to count small entities such as atoms and molecules.

• The mole is similar to counting items in groups, like a dozen eggs (12).

• Avogadro's Number (6.022 x 10^23) is utilized by scientists as a standard measure for counting small particles.

Avogadro's Number

• Avogadro's number allows scientists to quantify atoms, molecules, and other tiny items concisely.

• It equates to 6.022 x 10^23 units, where "units" can be atoms, molecules, or other entities.

• This makes the numbers listed on the periodic table more practical for calculations.

Molar Mass

• Molar mass is the grams of one mole of an element.

• For instance:

  • One mole of carbon (C) atoms equals 6.022 x 10^23 carbon atoms.

  • The molar mass of carbon is 12.01 grams (which indicates that 12.01 grams of carbon is one mole).

• Molar mass values for specific elements include:

  • Sodium (Na): 22.99 grams per mole

  • Chlorine (Cl): 35.45 grams per mole

• Sodium Chloride (NaCl) has a molar mass equal to the sum of its components' molar masses: 22.99 + 35.45 = 58.44 grams per mole.

Practice Problems

Problem 1: Moles of Neon in 34.5 Grams

• Task: Find the number of moles of neon in 34.5 grams.

• Given: 1 mole of neon weighs 20.18 grams (from the periodic table).

• Calculation: 34.5 g Ne × (1 mole Ne / 20.18 g Ne) = 1.71 moles of Neon.

Problem 2: Number of Neon Atoms

• Task: Determine the number of neon atoms in 34.5 grams.

• Approach: Use the conversion from moles to atoms.

• Calculation: 1.71 moles of Neon × (6.022 x 10^23 atoms/mole) ≈ 1.03 x 10^24 atoms.

Problem 3: Mass of Sodium Chloride from Formula Units

• Task: Calculate the mass in grams of 3.87 x 10^24 formula units of sodium chloride.

• Given: One mole of NaCl weighs 58.44 grams, and contains 6.022 x 10^23 formula units.

• Calculation:

  • Find moles: 3.87 x 10^24 units NaCl × (1 mole NaCl / 6.022 x 10^23 units NaCl) = 6.43 moles NaCl.

  • Find mass: 6.43 moles NaCl × 58.44 g/mol = 376 grams of NaCl.