Empirical formula : Definition , steps and numericals

🧪 Empirical Formula and Its Calculation

📌 What is an Empirical Formula?

The empirical formula of a compound is the simplest whole number ratio of atoms of each element present in that compound.

It tells us the basic composition of the compound but not the exact number of atoms like the molecular formula.

For example:

• Glucose molecular formula: C₆H₁₂O₆
• Empirical formula: CH₂O

🧠 Difference Between Empirical and Molecular Formula

• Empirical Formula: Simplest ratio (e.g., CH₂O)
• Molecular Formula: Actual number of atoms (e.g., C₆H₁₂O₆)

Note: Sometimes empirical and molecular formulas are the same (e.g., H₂O).

📝 Steps to Calculate the Empirical Formula

1. Write down the mass (or percentage) of each element.
2. Divide each mass by the element’s atomic mass (molar mass) to get moles.
3. Divide all moles by the smallest number of moles to get a ratio.
4. If the ratio is not a whole number, multiply by 2, 3, or 4 to make it whole.
5. Write the formula using these numbers as subscripts.

📚 Example 1: Simple Empirical Formula

A compound contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen. Find its empirical formula.

Step 1: Assume 100 g sample → C = 40g, H = 6.7g, O = 53.3g

Step 2: Moles of each:
C = 40 / 12 = 3.33
H = 6.7 / 1 = 6.7
O = 53.3 / 16 = 3.33

Step 3: Divide by smallest moles (3.33):
C = 1, H = 2.01, O = 1

Step 4: Approx. whole numbers → C:1, H:2, O:1

Empirical Formula = CH₂O

📘 Example 2: Tricky Ratio

A compound has 71.65% chlorine and 24.27% carbon and 4.07% hydrogen. Calculate its empirical formula.

Assume 100g sample:
Cl = 71.65g → 71.65 / 35.5 = 2.02 mol
C = 24.27g → 24.27 / 12 = 2.02 mol
H = 4.07g → 4.07 / 1 = 4.07 mol

Smallest moles = 2.02
Cl = 1, C = 1, H = 2

Empirical Formula = CClH₂

🔁 Empirical Formula from Molecular Formula

To find the empirical formula from a molecular one, divide all subscripts by their HCF.

Molecular: C₆H₁₂O₆ → divide by 6 → CH₂O

🧪 Real-World Uses

• Used in chemical analysis and laboratory experiments
• Helps determine unknown compound structures
• Used in pharmaceuticals and chemical manufacturing

✅ Summary

• Empirical formula shows simplest ratio
• Calculated using atomic masses and mole ratios
• Key steps: Mass → Moles → Ratio → Formula
• Always reduce to smallest whole numbers

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