UNIT 3 - Quantities in Chemical Reactions

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Chapter 6 - The Mole and Mole Calculations

n=N/NA

n = m/M

m/M = N/NA

    • n = moles (mol)

    • N = particles (atoms, molecules, formula units..) (particles/mol)

    • NA = avogadro's constant (6.02 x 10^23 particles/mol)

    • m = mass (g)

    • M = molar mass (mass of 1 mole of substance, found on periodic table) (g/mol)

Chapter 7 - % composition

% composition 2 methods:

    • law of definite proportions

    • mass of element / mass of compound x 100%

    • Molar Mass of element(s) / Molar Mass of compound x 100%

Empirical Formula (lowest ratio of elements)

    • mass --> moles

    • moles --> subscripts

    • subscripts --> divide by lowest

    • subscripts --> multiply if needed (to get whole #)

Molecular Formula (actual subscripts)

    • r = Molar mass of Molecular formula / Molar Mass of Empirical Formula

    • Molecular formula subscripts = r x Empirical Formula Subscripts

Hydrates

    • ionic compounds that crystallize with water in their structure

    • Mass % of water = (total mass of sample - mass of anhydrous) / total mass of sample x 100%

    • Molecular formula: find moles of anhydrous and moles of water, divide by lowest

C- H Analyzer

    • Find % comp of H in H2O (Molar mass H2 / Molar mass H2O)

    • Mass H = % comp H x Mass H2O

    • Repeat for C in CO2

    • If Oxygen present: mass of O = Initial mass of compound - mass of H - mass of O

    • Convert all mass to moles (n=m/M)

    • Put moles as subscripts, divide by lowest and multiply to get whole #

POEM - to help you remember

% to Mass

Mass to Mole

Divide by Smallest

Multiply until Whole

CHAPTER 8 - STOICHIOMETRY

    • Mole Ratios

    • Writing and balancing equations

    • Stoichiometry: convert to moles, use mole ratio, convert back to mass or particles

    • Limiting Reactant: find the reactant that produces the LEAST amount of product

    • % Yield = actual yield / theoretical yield x 100%