🎓 Prepared by students from Boğaziçi University

What is the Mole Concept?

The mole is a fundamental unit in chemistry that represents 6.022 × 10²³ particles (atoms, molecules, ions) — Avogadro's number. It links the macroscopic world (grams) to the atomic world.

Short answer

A mole is 6.022 × 10²³ particles. The mole equation n = m/M converts mass (m) to moles (n) using molar mass (M).

Converting Between Mass, Moles, and Particles

1
Mass (g)
Macroscopic amount you can measure
↓
2
÷ Molar Mass (g/mol)
Divide by the formula mass
↓
3
Moles (mol)
Intermediate step, count of particles
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4
× Avogadro's Number
Multiply by 6.022 × 10²³
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5
Number of Particles
Atoms, molecules, or ions

Try it: interactive calculator

Number of moles (n)

2mol

= 36.04/18.02

Mass (m)36.04 gMolar mass (M)18.02 g/mol

Step-by-step worked examples

How many moles are in 36.04 g of H₂O?

Given: mass = 36.04 g, molar mass of H₂O = 18.02 g/mol
n = m / M = 36.04 / 18.02 = 2.00 mol

What is the mass of 0.5 mol of CO₂?

Rearrange: m = n × M
Molar mass of CO₂ = 44.01 g/mol
m = 0.5 × 44.01 = 22.01 g

How many molecules in 1 mol of O₂?

n = 1 mol
Number of molecules = n × Avogadro's number
= 1 × 6.022 × 10²³ = 6.022 × 10²³ molecules

Flashcards

Quick quiz

Q1.How many moles in 44.01 g of CO₂?

Correct answer: B. n = 44.01 / 44.01 = 1.0 mol.

Q2.Mass of 2.5 mol of H₂O (M = 18.02 g/mol)?

Correct answer: D. m = n × M = 2.5 × 18.02 = 45.05 g.

Q3.Avogadro's number is…

Correct answer: B. Avogadro's number is 6.022 × 10²³ particles per mole.

Q4.What links mass to particle count?

Correct answer: B. Molar mass converts g to mol; Avogadro's number converts mol to particles.

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Common mistakes

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One mole of all substances is the same mass. — Correct: One mole has the same number of particles (6.022 × 10²³) but different masses — depends on molar mass.

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Avogadro's number is the mass of one mole in grams. — Correct: It's the number of particles in one mole (6.022 × 10²³).

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The mole concept only applies to molecules. — Correct: It applies to atoms, molecules, ions, and any particles.

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Forget to use the molar mass in calculations. — Correct: Molar mass is essential — it converts between mass and moles.

FAQ

What is the mole formula?

n = m / M, where n = moles, m = mass (g), M = molar mass (g/mol).

Why is the mole important in chemistry?

It connects the macroscopic world (measurable grams) to the atomic world (individual particles).

How many particles in one mole?

6.022 × 10²³ — Avogadro's number. Same for any substance.

Can I calculate mass from moles?

Yes, rearrange the equation: m = n × M.