Mole Conversions

Introduction to the Mole

• The mole is a fundamental unit in chemistry used to count particles (atoms, molecules, etc.).

• Defined as 6.02 x 10²³, known as Avogadro's number.

• Important to memorize Avogadro's number for calculations.

Avogadro and the Mole

• Avogadro's experiments with gases at the same temperature and pressure revealed that equal volumes of different gases contain equal numbers of particles.

• For example, at STP, one mole of any gas occupies a volume of 22.4 liters.

• This led to the identification of Avogadro's number as a counting unit, similar to a dozen which represents 12 of anything.

Concept of Counting Units

• Similar to a dozen: 1 mole = 6.02 x 10²³ of any item, regardless of what that item is.

• Example: 1 mole of pencils = 6.02 x 10²³ pencils, 1 mole of people = 6.02 x 10²³ people.

• While quantities count the same, their masses will differ based on the substance.

Moles as a Linking Unit

• The mole acts as a bridge between mass (grams) and number of entities (molecules/atoms).

• Changes in mass can lead to matching mole quantities, but the actual masses will vary by substance.

Understanding Conversions

• Proficiency in conversions is crucial for applying the concepts of moles.

• Review common conversions from gram to mole, mole to molecule, and other related processes.

Example Conversion: Grams to Moles

• Problem: How many moles are in 4.56 g of sodium chloride (NaCl)?

• Given: 4.56 g of NaCl.

• Conversion required using molar mass of sodium chloride.

• Sodium (Na): 22.99 g/mol and Chlorine (Cl): 35.45 g/mol.

  • Molar mass of NaCl = 22.99 + 35.45 = 58.44 g/mol.

• Setup conversion:

  [ \text{Moles} = \frac{4.56 \text{ g NaCl}}{58.44 \text{ g/mol}} \approx 0.078 \text{ mol} ]

Example Conversion: Moles to Molecules

• Problem: Find molecules in 1.7 x 10⁻¹⁵ moles of NaCl.

• Conversion using Avogadro's number (6.02 x 10²³).

• Setup conversion:

  [ \text{Molecules} = 1.7 \times 10^{-15} \text{ moles NaCl} \times 6.02 \times 10^{23} \text{ molecules/mole} \approx 1.0 \times 10^9 \text{ molecules NaCl} ]

Example Conversion: Grams to Atoms

• Problem: How many atoms in 54.3 g of copper(II) nitrate (Cu(NO₃)₂)?

• Find molar mass of Cu(NO₃)₂:

  • Cu: 63.55 g/mol, N: (2) * 14.01 = 28.02 g/mol, O: (6) * 15.999 = 95.994 g/mol.

  • Total molar mass: 63.55 + 28.02 + 95.994 = 187.57 g/mol.

• Conversion to moles:

  • [ \text{Moles of Cu(NO}_3)_2 = \frac{54.3 \text{ g}}{187.57 \text{ g/mol}} \approx 0.289 \text{ moles} ]

• Convert moles to molecules:

  • [ \text{Molecules} = 0.289 \text{ moles} \times 6.02 \times 10^{23} \approx 1.74 \times 10^{23} \text{ molecules} ]

• Convert molecules to atoms:

  • Each molecule has 9 atoms (Cu: 1, N: 2, O: 6).

  • [ \text{Atoms} = 1.74 \times 10^{23} \text{ molecules} \times 9 ext{ atoms/molecule} \approx 1.57 \times 10^{24} ext{ atoms} ]

Conclusion

• Understanding mole conversions is crucial for stoichiometry and further chemistry concepts.

• Practice various conversion problems to become proficient.

• The mole links grams, moles, atoms, and molecules in analytical chemistry.