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What is the Molecular Formula?
Grade Level:
Class 10
AI/ML, Physics, Biotechnology, Space Technology, Chemistry, Engineering, Medicine
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 complete recipe that lists every single ingredient and its quantity in a dish.
Simple Example
Quick Example
Imagine you're making chai. If the recipe says '1 cup water, 1/2 cup milk, 1 teaspoon sugar, 1/4 teaspoon tea leaves', that's like its molecular formula. It tells you the exact amount of each ingredient. For water, its molecular formula is H2O, meaning it has exactly 2 Hydrogen atoms and 1 Oxygen atom.
Worked Example
Step-by-Step
Let's find the molecular formula of a compound if its empirical formula is CH2O and its molecular mass is 180 g/mol.
Step 1: Calculate the empirical formula mass (EFM) for CH2O.
Carbon (C) = 12 g/mol, Hydrogen (H) = 1 g/mol, Oxygen (O) = 16 g/mol.
EFM = (1 x 12) + (2 x 1) + (1 x 16) = 12 + 2 + 16 = 30 g/mol.
---Step 2: Calculate the 'n' factor (a whole number multiplier).
n = Molecular Mass / Empirical Formula Mass
n = 180 g/mol / 30 g/mol = 6.
---Step 3: Multiply the empirical formula by 'n' to get the molecular formula.
Molecular Formula = n x (Empirical Formula)
Molecular Formula = 6 x (CH2O) = C(1x6)H(2x6)O(1x6) = C6H12O6.
The molecular formula is C6H12O6.
Why It Matters
Knowing the molecular formula is crucial in fields like Biotechnology for designing new medicines, and in Engineering for creating new materials. Doctors use it to understand how drugs affect our bodies, and scientists at ISRO might use it to study compounds found in space.
Common Mistakes
MISTAKE: Confusing molecular formula with empirical formula, thinking they are always the same. | CORRECTION: Remember, the molecular formula shows the *exact* number of atoms, while the empirical formula shows the *simplest whole-number ratio* of atoms. They are only the same if the simplest ratio is also the exact number.
MISTAKE: Incorrectly calculating the empirical formula mass by using molecular mass values. | CORRECTION: Always use the atomic masses of individual elements to calculate the empirical formula mass, not the given molecular mass.
MISTAKE: Making calculation errors when finding the 'n' factor or when multiplying the empirical formula. | CORRECTION: Double-check your arithmetic, especially when dividing the molecular mass by the empirical formula mass and then multiplying the subscripts.
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 C2H3 and a molecular mass of 54 g/mol. Determine its molecular formula. (Atomic mass C=12, H=1) | ANSWER: C4H6
QUESTION: If a compound contains 40% Carbon, 6.67% Hydrogen, and 53.33% Oxygen, and its molecular mass is 90 g/mol, what is its molecular formula? (Hint: First find the empirical formula). | ANSWER: C3H6O3
MCQ
Quick Quiz
Which of the following represents the molecular formula of glucose?
CH2O
C6H12O6
C12H22O11
C2H4O2
The Correct Answer Is:
B
C6H12O6 is the exact number of atoms in one molecule of glucose. CH2O is its empirical formula, representing the simplest ratio.
Real World Connection
In the Real World
When you buy medicines from a chemist, the chemical name on the packaging often relates to its molecular formula. For example, 'Paracetamol' has a specific molecular formula (C8H9NO2) that scientists and doctors use to understand how it works in your body to reduce fever or pain. This formula helps pharmacists ensure you get the correct medicine.
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 of a chemical element. | COMPOUND: A substance formed when two or more chemical elements are chemically bonded together.
What's Next
What to Learn Next
Great job understanding molecular formulas! Next, you should learn about 'Balancing Chemical Equations'. This will help you see how different molecular formulas react with each other to form new substances, just like following a detailed recipe to cook a meal.
