Concentration of solutions: units, practice, pitfalls
Quantitative chemistry • Concentration of solutions
Flashcards
Test your knowledge with interactive flashcards
Key concepts
What you'll likely be quizzed about
Definition and main formula
Concentration measures amount of solute per volume of solution. The primary formula uses amount in moles (n) and volume in cubic decimetres (V): c = n / V. Incorrect volume units cause systematic errors in the result because the formula requires volume in dm3 when reporting concentration in mol dm-3.
Common units and their relationships
Mol dm-3 (also written mol L-1) expresses moles per cubic decimetre. Cubic centimetres (cm3) and cubic decimetres (dm3) relate by 1 dm3 = 1000 cm3. Mass concentration uses g dm-3 or g L-1 and requires conversion from mass to moles using molar mass when a molar concentration is required. Failure to convert volume from cm3 to dm3 produces an answer too large by a factor of 1000.
Converting mass to moles
Amount in moles equals mass divided by relative molecular or atomic mass: n = mass / Mr. Mass reported in grams requires no unit conversion for this formula. Using mass in kilograms without converting to grams produces an answer smaller by a factor of 1000 and breaks subsequent concentration calculations.
Volume handling and limiting factors
Volume in titrations or dilutions refers to final solution volume, not the sum of separate component volumes unless stated. Temperature changes alter solution density but do not affect calculations that use measured volume in dm3. Concentration calculations assume complete dissolution and no reaction side processes unless otherwise specified.
Rearrangement and algebra
Rearrangement of c = n / V yields n = c × V and V = n / c. Algebraic errors cause wrong intermediate values and incorrect final answers. Substituting values with inconsistent units causes magnitude errors even when algebra is correct.
Key notes
Important points to keep in mind