MCAT / FREE INTRODUCTION
See what dilution preserves
From particle model to equation
Read the free introduction transcript
01 · Predict before you calculate
Five millilitres. Zero point two four moles per litre. Add solvent until the total solution volume reaches thirty millilitres. Before using an equation, predict: should the concentration rise, fall, or stay the same? It falls. We have more space for the same amount of solute. Keep that prediction. It will help you catch a reversed ratio later.
02 · Follow the conserved quantity
Watch the same twelve symbols spread through a larger volume. They stand for a fixed amount of solute, not twelve literal molecules in the sample. Six times the volume means one sixth of the concentration. Zero point two four divided by six gives zero point zero four zero moles per litre. The amount stays at one point two zero millimoles. The concentration changes because the total volume changes. That is dilution in this model: add solvent, conserve solute, and use the final total volume.
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The full lesson adds a decision pause, a worked explanation, and three follow-up cases with reasoning feedback.
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Scope and sources
Original idealized chemistry models. Assume a homogeneous solution, no reaction or solute loss, and the stated final solution volume. Particle counts are schematic, not molecular-scale measurements.
- OpenStax Chemistry 2e — 3.3 Molarity
Molarity and conservation of solute during dilution. Original numerical examples and diagrams; no source questions or artwork reproduced.
Sources checked 3 November 2026. Original QuietStride teaching material with synthetic narration and illustrated diagrams. Independent preparation; no exam-provider affiliation or endorsement.