IBDP Chemistry: Stoichiometry & Moles Core

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The Mole Concept Definition

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The mole is the SI unit for amount of substance. One mole contains exactly 6.02214076 * 10^23 elementary entities (atoms, molecules, ions, etc.), known as Avogadro's constant (N_A). This number corresponds to the number of atoms in 12 grams of Carbon-12.

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Calculating Moles from Mass

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Use the formula n = m / M, where n is the amount in moles, m is the mass in grams, and M is the molar mass in g/mol. Molar mass is calculated by summing the relative atomic masses (A_r) of all atoms in the chemical formula.

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Empirical vs. Molecular Formula

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The **empirical formula** shows the simplest whole-number ratio of atoms of each element in a compound. The **molecular formula** shows the actual number of atoms of each element in a molecule. For example, glucose has an empirical formula of CH2O and a molecular formula of C6H12O6.

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Determining Empirical Formula from Mass Data

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1. Convert mass of each element to moles (n = m/M). 2. Divide all mole values by the smallest number of moles calculated. 3. If the results are not whole numbers, multiply all by an integer to convert them to whole numbers (e.g., if you get 1.5, multiply all by 2).

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Reacting Mass Calculations

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Use stoichiometric ratios from the balanced equation to convert moles of one substance to moles of another. Process: Mass A -> Moles A (divide by M_A) -> Moles B (multiply by mole ratio) -> Mass B (multiply by M_B).