Theme B — The Particulate Nature of Matter
B.3.2 Amount of Substance — IB Physics HL Revision Notes & Topical Questions
5 min read 9 parts Lesson 26 of 53 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
B.3.2 Amount of Substance — IB PHYSICS SL notes: Use the mole, the Avogadro constant and molar mass to relate mass, number of particles and amount of substance.Mole = the amount of substance that contains as many elementary entities as there are atoms in 12 g of carbon-12.It is o…
- Why needed
- Naming the entity
- Data booklet
- Molar mass M
- Numerically
- Other values
Part 1 of 7The mole
Mole
Mole the amount of substance that contains as many elementary entities as there are atoms in 12 g of carbon-12.
- It is one of the seven SI base units and measures the amount of substance, not mass.
Avogadro constant
- NA = 6.02 × 1023 mol−1 (exactly 6.02214076 × 1023).
Why needed
- Why needed samples contain an unimaginably large number of particles, so a counting unit is used, like a dozen.
Naming the entity
- "1 mol of oxygen atoms" differs from "1 mol of oxygen molecules".
Data booklet
- Data booklet the value of NA is given.
Part 2 of 7Number of particles
Number of particles
Equations
- N = nNA and n = N/NA.
- N is the number of particles (atoms or molecules).
- n is the number of moles.
Units
- Units n carries the mole, N is a pure number and NA carries mol−1.
Example
- 2.0 mol of helium contains 2.0 × 6.02 × 1023 = 1.2 × 1024 atoms.
Part 3 of 7Molar mass
Molar mass M
Molar mass M the mass of the substance divided by its amount, M = m/n, in g mol−1 (or kg mol−1 in SI).
Numerically
- Numerically it equals the relative atomic mass, or relative molecular mass, from the periodic table.
Element
- Element one mole has a mass in grams equal to its relative atomic mass; helium has M = 4.0 g mol−1.
Compound
- Compound add the atomic masses of all the atoms; water is (2 × 1) + 16 = 18 g mol−1.
Other values
- Other values oxygen gas O2 has 32 g mol−1 and carbon dioxide 44 g mol−1.
Amount in a sample
- Amount in a sample n = m/M.What the symbols mean: n = amount of substance (mol) · m = mass (g) · M or Mr = molar mass (g mol−1, numerically equal to Mr)
Units
- Units if M is in g mol−1, then m must be in grams, so the mass is in grams, not kilograms.
Part 4 of 7Combined relations
Combined relations
Particles in a given mass
- N = (m/M)NA.
Mass of one particle
- Mass of one particle mparticle = M/NA.
In kilograms
- In kilograms convert M to kg mol−1 first.
Chain
- Chain mass to moles to number of particles, or the reverse.
Size check
- Size check a few grams of a light substance contain 1022 to 1024 particles, and one molecule has a mass of order 10−26 kg.
Significant figures
- Significant figures give the same number as the data.
Part 5 of 7Unified atomic mass unit
Unified atomic mass unit
Unit u
- Unit u one twelfth of the mass of a carbon-12 atom, 1.66 × 10−27 kg.
Molecule of relative molecular mass 32
- Molecule of relative molecular mass 32 its mass is 32 u.
Reason
- NA is defined so that 1 u × NA = 1 g mol−1.
Part 6 of 7Link to the gas laws
Ideal gas equation
- Ideal gas equation n appears in pV = nRT.
Equal amounts
- Equal amounts equal amounts of any ideal gas at the same temperature and pressure occupy the same volume.
Molar volume
- Molar volume at 273 K and 1.01 × 105 Pa one mole occupies about 22.4 dm3 (2.24 × 10−2 m3).
Kinetic theory
- N and the mass of one molecule are used with kB = R/NA = 1.38 × 10−23 J K−1.
Part 7 of 7More from the specification
More from the specification
Avogadro constant and mole calculations
- Avogadro constant and mole calculations multiplying molar quantity by the Avogadro number provides an exact means to count microscopic particles.
Amount of substance
- Amount of substance the mole counts particles, with one mole containing the Avogadro number of particles.
Molar mass
- Molar mass mass of one mole in grams, linking mass to number of particles.
Gas quantities
- Gas quantities average kinetic energy of molecules and number of moles relate through the ideal gas law.
Avogadro constant
- Avogadro constant about 6.02 times ten to the 23 per mole.
Energy and momentum
- Energy and momentum gas pressure and speed link molecular momentum changes to measurable macroscopic quantities.
Thermodynamic temperature
- Temperature in kelvin, to which an ideal gas's internal energy is proportional.
Momentum
- P = mv, a vector.
Proportional
- Changing by the same factor as another quantity.
Force
- A push or pull measured in newtons.
Collision
- Short interaction with large internal forces.
Kinetic energy
- K = ½mv2, energy of motion.
Boltzmann constant
- K = R/NA, the gas constant per molecule
Internal energy
- Total kinetic and potential energy of the particles in a system
Average speed
- Total distance divided by total time.
Key terms
| Term | Meaning |
|---|---|
| Mole | Amount of substance containing as many entities as atoms in 12 g of carbon-12 |
| Avogadro constant | NA = 6.02 × 1023 mol−1 |
| Molar mass | Mass of one mole of a substance, in g mol−1 |
| Relative atomic mass | Mass of an atom compared with one twelfth of carbon-12 |
| Unified atomic mass unit | One twelfth of the mass of a carbon-12 atom, 1.66 × 10−27 kg |
| Molar volume | Volume of one mole of ideal gas, about 22.4 dm3 at 273 K and 1.01 × 105 Pa |
Avoid these mistakes
1
Using grams with kg mol−1 — keep the units consistent.
2
Forgetting to name the entity — atoms and molecules differ.
3
Treating the mole as a mass — it is an amount of substance.
4
Multiplying instead of dividing to get n from N — n = N/NA.
5
Using molar mass in g mol−1 to give kilograms — the mass is in grams.
Marked practiceQuizzes for this lesson
Last updated:
\n