Chemistry Chapter: Dimensional Analysis & Moles

Study Notes

Dimensional analysis is used to convert between different units in calculations.
Showing how units cancel is crucial in dimensional analysis.
Moles are a unit that relates the number of particles (atoms or molecules) to mass.
Avogadro's number (6.02 x 10²³) links the number of moles to the number of particles.
The molar mass of a substance is the mass in grams of one mole of that substance. It equals the substance's atomic mass in grams.

Example problems include calculating the number of atoms in a given number of moles of aluminum (Al).
Another example is calculating the number of moles containing a certain number of formula units of zinc chloride (ZnCl₂).

A mole of an element has a mass equal to its atomic mass in grams.
A mole of a compound has a mass equal to the sum of the atomic masses of its constituent elements.
The molar mass of a substance is crucial for converting between mass and moles or particles in a calculation.

Atomic mass units (amu) are based on the number of protons and neutrons in an atom.
The periodic table's average atomic mass is based on the abundance of different isotopes of an element.
Atomic mass is not always a whole number due to the presence of different isotopes for each element.

Moles are based on the number of atoms present in 12 grams of carbon-12.
Calculating the number of atoms in 12 grams of carbon-12 led to Avogadro's number.

Convert between mass, moles, and particles.
Conversion factors using moles and molar mass help solve problems involving these quantities.

Example 1: Calculating the molar mass of potassium hydroxide (KOH). The calculation involved adding the atomic masses of K, O, and H to determine the molar mass.
Example 2: Determining the number of moles in 2.85 grams of calcium carbide (CaC₂). Using dimensional analysis, this problem gives the answer of 0.0445 moles.
Example 3: Determining the mass of 1.32 moles of calcium (Ca). Using the conversion factor of molar mass (40.08g/mol), the answer is 52.9 grams.
Example 4: Calculating the number of atoms in 4.6 grams of silver (Ag). This involved a two-step calculation to determine the number of atoms.

Example: Calculating the mass of 1.60 x 10²⁴ atoms of manganese (Mn). The calculated answer is 146 grams. Note all conversion problems are solved using dimensional analysis.