General chemistry · Stoichiometry

Mole Conversions

22 terms · by ineedtostudy · updated 21 hours ago

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Terms in this set

Mole (mol)

The amount of a substance containing 6.022 × 10²³ particles — atoms, molecules, ions or formula units. It is a counting word, like "dozen".

Avogadro's number

6.022 × 10²³ particles per mole. The bridge between things you can count and things you can weigh.

Molar mass

The mass of one mole, in g/mol. Numerically the same as the formula mass in amu, so it is read straight off the periodic table.

The mole map

grams ↔ moles ↔ particles, with litres of gas hanging off moles. Everything routes through moles; nothing converts grams straight to particles.

Grams → moles

Divide by the molar mass. moles = grams ÷ (g/mol).

Moles → grams

Multiply by the molar mass. grams = moles × (g/mol).

Moles → particles

Multiply by 6.022 × 10²³.

Particles → moles

Divide by 6.022 × 10²³.

Grams → particles

Two steps, always through moles: divide by the molar mass, then multiply by 6.022 × 10²³.

Molar volume at STP

One mole of an ideal gas occupies 22.4 L at STP (0 °C and 1 atm). Litres ÷ 22.4 gives moles; moles × 22.4 gives litres.

Mole ratio

The ratio of the coefficients in a balanced equation. It is the only legitimate way to cross from one substance to another.

Dimensional analysis

Write every conversion as a fraction whose unwanted unit cancels. If the units do not cancel to the unit you want, the setup is wrong before any arithmetic happens.

Molar mass of H₂O

18.02 g/mol — 2 × 1.008 + 16.00.

Molar mass of CO₂

44.01 g/mol — 12.01 + 2 × 16.00.

Molar mass of NaCl

58.44 g/mol — 22.99 + 35.45.

36.0 g of H₂O in moles

36.0 ÷ 18.02 = 2.00 mol.

2.00 mol of H₂O in molecules

2.00 × 6.022 × 10²³ = 1.20 × 10²⁴ molecules.

0.500 mol of CO₂ in grams

0.500 × 44.01 = 22.0 g.

Percent composition

(mass of the element in one mole ÷ molar mass of the compound) × 100.

Empirical formula from percentages

Assume 100 g, turn each percentage into moles, divide every result by the smallest, then multiply up to whole numbers.

Limiting reactant

Convert every reactant to moles, divide each by its coefficient, and the smallest answer is the reactant that runs out first.

Percent yield

The theoretical yield comes from the limiting reactant through the mole ratio. Percent yield = (actual ÷ theoretical) × 100.