Empirical Formula

<aside> 💡 Simplest ratio of elements in a substance

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3 Types of problems (Easiest → Hardest)

1) Given Moles of all elements

<aside> 💡 Divide by smallest mole

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Example

0.75 mol C / 0.25 = 3 C

1.5 mol H / 0.25 = 6 H

0.25 mol O / 0.25 = 1 O

$C_3H_6O$

BUT If instead 0.5 mol O

0.75 mol C / 0.50 = 1.5 C * 2

1.5 mol H / 0.50 = 3 H * 2

0.50 mol O / 0.50 = 1 O * 2

$C_3H_6O_2$

Multiply by 2 to get rid of common decimal

**Common Decimals are when you can multiply by a whole number to make sure all the elements have a whole number of moles

2) Given masses of all elements

<aside> 💡 (Grams → Moles) then /smallest mol

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3) Given percent masses of all elements

<aside> 💡 (Convert percentages to grams assuming 100g sample → Grams to Moles) then /smallest mol

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Molecular Formula

• Actual number of each atom in a molecule

Steps to Determine Molecular Formula:

1. Find Empirical Formula Mass: Calculate the mass of the empirical formula.
2. Determine Molar Mass Ratio: Divide the compound's molar mass by the empirical formula mass.
3. Multiply Empirical Formula: Use the ratio to multiply the subscripts in the empirical formula to get the molecular formula.

<aside> 💡 $(mol_{M.F.})/(mol_{E.F.})$ = Multiplier for E.F.

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