What is Molecular Formula?

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Grade Level:

Class 12

AI/ML, Physics, Biotechnology, FinTech, EVs, Space Technology, Climate Science, Blockchain, Medicine, Engineering, Law, Economics

Definition

What is it?

The molecular formula tells us the exact number of atoms of each element present in one molecule of a compound. It's like a detailed ingredient list for a chemical compound, showing every single atom.

Simple Example

Quick Example

Imagine you're making a special chai mix. The empirical formula might tell you the ratio of ginger to cardamom is 1:1. But the molecular formula would tell you exactly how many grams of ginger and how many grams of cardamom are in one serving of your chai. For glucose, the empirical formula is CH2O, but the molecular formula is C6H12O6, showing exactly 6 carbon, 12 hydrogen, and 6 oxygen atoms.

Worked Example

Step-by-Step

Let's find the molecular formula of a compound if its empirical formula is CH2 and its molecular mass is 28 g/mol.

Step 1: Calculate the empirical formula mass (EFM) for CH2.
EFM = (1 x atomic mass of C) + (2 x atomic mass of H)
EFM = (1 x 12) + (2 x 1) = 12 + 2 = 14 g/mol.

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Step 2: Determine the value of 'n' using the formula: n = Molecular Mass / Empirical Formula Mass.
n = 28 g/mol / 14 g/mol = 2.

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Step 3: Multiply the subscripts in the empirical formula by 'n' to get the molecular formula.
Molecular Formula = (CH2)n = (CH2)2.

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Step 4: Distribute 'n' to each element.
Molecular Formula = C(1x2)H(2x2) = C2H4.

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Answer: The molecular formula of the compound is C2H4.

Why It Matters

Understanding molecular formulas is crucial in medicine for designing new drugs, in biotechnology for creating new materials, and in environmental science to understand pollutants. Scientists and engineers use this knowledge to create everything from advanced batteries for EVs to new materials for space technology.

Common Mistakes

MISTAKE: Confusing empirical formula with molecular formula. | CORRECTION: Remember, empirical formula is the simplest whole-number ratio, while molecular formula is the actual number of atoms.

MISTAKE: Incorrectly calculating the empirical formula mass. | CORRECTION: Always double-check the atomic masses of elements and ensure correct multiplication and addition.

MISTAKE: Forgetting to multiply ALL subscripts in the empirical formula by 'n'. | CORRECTION: Make sure to apply the 'n' value to every element's subscript in the empirical formula.

Practice Questions

Try It Yourself

QUESTION: What is the molecular formula of hydrogen peroxide if its empirical formula is HO and its molecular mass is 34 g/mol? | ANSWER: H2O2

QUESTION: A compound has an empirical formula of C3H5O and a molecular mass of 114 g/mol. What is its molecular formula? (Atomic masses: C=12, H=1, O=16) | ANSWER: C6H10O2

QUESTION: If the empirical formula of a hydrocarbon is CH and its vapor density is 13, find its molecular formula. (Hint: Molecular mass = 2 x Vapor Density) | ANSWER: C2H2

MCQ

Quick Quiz

Which of the following represents the molecular formula?

The simplest ratio of atoms in a compound

The exact number of atoms of each element in a molecule

The arrangement of atoms in space

The mass of one mole of the compound

The Correct Answer Is:

The molecular formula specifically shows the exact count of each type of atom in a molecule. Option A describes the empirical formula, while C and D describe other aspects of compounds.

Real World Connection

In the Real World

When a food scientist at a company like Britannia or Amul develops a new biscuit or dairy product, they need to know the exact molecular formulas of ingredients like sugars (C6H12O6) or fats to ensure proper nutrition, taste, and shelf life. This precision helps them create safe and delicious food for everyone.

Key Vocabulary

Key Terms

MOLECULAR MASS: The sum of the atomic masses of all atoms in a molecule. | EMPIRICAL FORMULA: The simplest whole-number ratio of atoms in a compound. | ATOMIC MASS: The mass of an atom, typically measured in atomic mass units (amu). | COMPOUND: A substance formed when two or more chemical elements are chemically bonded together.

What's Next

What to Learn Next

Next, you should explore 'Empirical Formula' to understand how it relates to the molecular formula and how to calculate it from percentage composition. This will give you a complete picture of how we describe chemical compounds!