MYP Chemistry: Concentration & Dilution FAQ

Start by identifying what's given and what's asked — moles, volume, or concentration — then pick the right formula: concentration = moles ÷ volume (mol/dm³), or for dilutions, C₁V₁ = C₂V₂. Show units at every step. According to the MYP Sciences guide, criterion C rewards a clear, logical processing of quantitative data, not just a final number.

Concentration equals the amount of solute (in moles) divided by the volume of solution (in dm³), giving units of mol/dm³. Some MYP tasks use g/dm³ instead, so always check which unit the question expects before you calculate — examiners mark units as part of accuracy, not as an afterthought.

Concentration tells you how much solute is packed into a given volume of solution — it's a measurement. Dilution is the process of adding solvent (usually water) to lower that concentration, without changing the total moles of solute present. Students often confuse the two because both use the same C₁V₁ = C₂V₂ relationship.

Identify the known concentration and volume before dilution (C₁, V₁), the target concentration after dilution (C₂), then rearrange to find the missing volume (V₂). This equation works because the moles of solute don't change during dilution — only the total volume of solution increases.

Concentration and dilution calculations are usually assessed under Criterion C: Processing and Evaluating, which rewards accurate data collection, correct use of significant figures, and appropriate units in numerical processing. A well-labelled calculation with clear working scores higher than a correct answer with no method shown.

The most common mistake I see is confusing the volume of water added with the final total volume — they're not the same number. Second most common: forgetting to convert cm³ to dm³ before applying the concentration formula, which throws the answer out by a factor of 1000.

Practice past-style questions until the C1V1 = C2V2 rearrangement is automatic, and always write out units alongside numbers — examiners specifically credit correct unit use in Criterion C. Weak students calculate; strong students calculate and explain why the method makes sense chemically.

Dilution lets chemists work safely and accurately with solutions that would otherwise be too concentrated to handle or measure precisely — hospital IV drug doses and school titration standards are diluted from stock solutions for exactly this reason. In MYP practicals, you'll often dilute a stock solution to create a range of concentrations for a graph.

A serial dilution halves (or reduces by a fixed factor) the concentration at each step by taking a set volume of the previous solution and adding an equal or larger volume of solvent. It's used to create a concentration range for calibration curves without preparing each solution from scratch.

No — MYP concentration and dilution is the foundation for DP Chemistry, not a separate harder topic. DP adds molar concentration in more complex multi-step calculations, buffer solutions, and titration curve analysis, but the core C1V1 = C2V2 logic taught at MYP 4-5 carries straight through unchanged.

Conceptual understanding first, always. A student who memorises C1V1 = C2V2 without understanding that moles stay constant during dilution will freeze the moment a question is phrased differently. In my experience, students who can explain the "why" in one sentence rarely make the unit-conversion mistakes that cost marks.