In IB Chemistry, concentration appears across stoichiometry, acids and bases, titrations, equilibrium, and even redox topics. Although the calculations themselves are usually straightforward, many students lose marks because they don’t remember the correct units or when to use them. This guide breaks down everything you need to know about concentration units in an IB-friendly format.
Quick Start Checklist
The primary concentration unit in IB Chemistry is:
- mol dm⁻³ (moles per cubic decimeter)
You may also see:
- g dm⁻³ (grams per cubic decimeter)
- % concentration (percentage by mass or volume)
- ppm (parts per million)
- mol L⁻¹ (used interchangeably with mol dm⁻³ in some contexts)
But mol dm⁻³ is the standard for stoichiometry, titrations, and equilibria.
Strengthening your general chemistry skills—especially lab accuracy—helps when working with concentration calculations:
https://www.revisiondojo.com/blog/tips-to-improve-your-lab-skills-for-ib-chemistry
Why IB Chemistry Uses mol dm⁻³
1. Direct link to moles
Since moles are the foundation of most quantitative chemistry, expressing concentration as moles per volume makes calculations fast and consistent.
2. Works seamlessly with common formulas
Many essential IB formulas use molarity directly:
- n = c × V for solutions
- Kc expressions
- Titration calculations
- Reaction stoichiometry in aqueous solutions
Using mol dm⁻³ keeps everything in compatible units.
3. Matches laboratory practice
In most school labs, volumes are measured in cm³ or dm³, and solutions are prepared based on molar concentration. This aligns theory with hands-on skills, which is especially important in IA investigations.
To understand how lab expectations compare across IB sciences, see:
https://www.revisiondojo.com/blog/ib-biology-ia-vs-chemistry-ia-which-is-more-challenging
Converting Units (IB-Style)
dm³ and cm³
1 dm³ = 1000 cm³
1 dm³ = 1 liter
If volume is given in cm³, convert it:
V(dm³) = V(cm³) ÷ 1000
IB examiners expect you to handle this conversion without prompting.
Concentration Units You Must Know
1. mol dm⁻³
The standard for:
- titrations
- acid–base calculations
- equilibrium (Kc)
- rates
- stoichiometry
2. g dm⁻³
Useful for:
- solution preparation steps
- problems involving mass rather than moles
To convert:
c(mol dm⁻³) = c(g dm⁻³) ÷ molar mass
3. ppm (parts per million)
Seen in environmental chemistry and water analysis.
1 ppm ≈ 1 mg per dm³.
You can explore how chemistry connects to environmental pathways here:
https://www.revisiondojo.com/blog/ib-ess-vs-ib-chemistry-which-is-more-useful-for-environmental-careers
Sample IB Question
What is the concentration of a solution that contains 0.05 mol of NaOH in 250 cm³?
- Convert volume:
250 cm³ → 0.250 dm³ - Use c = n ÷ V:
c = 0.05 ÷ 0.25 = 0.20 mol dm⁻³
This structure—conversion, formula, answer—is exactly what earns full marks on Paper 2.
For subject comparison and planning your study strategy across sciences, see:
https://www.revisiondojo.com/blog/ib-biology-vs-ib-chemistry-which-science-is-better-for-you
Frequently Asked Questions
1. Are mol L⁻¹ and mol dm⁻³ the same?
Yes. 1 liter = 1 dm³, so mol L⁻¹ is equivalent to mol dm⁻³. IB prefers mol dm⁻³, but either is acceptable unless the question specifies otherwise.
2. Does IB use molarity (M)?
IB avoids the capital M notation used in some textbooks. Instead, it prefers mol dm⁻³ to avoid confusion. Always write the full unit on exam papers.
3. Can you use mol cm⁻³?
Technically yes, but it is almost never used because it gives very small values. IB examiners expect dm³ unless a question explicitly uses cm³ for volume, in which case you convert.
Conclusion
The main unit for concentration in IB Chemistry is mol dm⁻³, which aligns with mole-based calculations, equilibrium expressions, titration work, and laboratory practice. Understanding when and how to use other units—like g dm⁻³ and ppm—helps you confidently solve quantitative problems across both SL and HL. With RevisionDojo’s chemistry-focused learning guides, you can build accuracy and confidence across the entire course.
