Calculate mass from solution concentration
Quantitative chemistry • Amount of substance and mass
Flashcards
Test your knowledge with interactive flashcards
Key concepts
What you'll likely be quizzed about
Definition of concentration (mass per volume)
Concentration (mass concentration) quantifies the mass of solute dissolved in a given volume of solution. The standard unit for calculations in this context is grams per cubic decimetre (g/dm3), sometimes written as g dm-3. Cause: adding more solute increases the mass per volume. Effect: concentration increases proportionally when the mass of solute increases while volume remains constant.
Core formula and rearrangements
The primary equation links concentration, mass and volume: concentration = mass ÷ volume. Rearranged forms enable different calculations: mass = concentration × volume and volume = mass ÷ concentration. Cause: knowing any two variables allows calculation of the third by algebraic rearrangement. Effect: incorrect units or omission of conversions causes wrong answers; unit consistency prevents errors.
Unit conversions for volume
Standard calculation uses volume in cubic decimetres (dm3). Conversion rule: 1 dm3 = 1000 cm3. Cause: concentrations in g/dm3 require volume expressed in dm3 to yield mass in grams directly. Effect: when volume is given in cm3, divide by 1000 before using mass = concentration × volume. Example: 250 cm3 becomes 0.250 dm3.
Link with amount (HT) and molar concentration
Molar concentration (c, in mol dm-3) relates to mass concentration (ρ, in g dm-3) through the molar mass (Mr): ρ = c × Mr. Cause: moles × molar mass produce mass, so molar concentration × molar mass × volume produces mass of solute. Effect: mass of solute = c × Mr × volume (with volume in dm3). This relation allows conversion between molar and mass-based calculations when Mr is available.
Limiting factors and practical considerations
Solubility limits restrict the maximum mass that dissolves at a given temperature. Temperature changes alter solution volume slightly and therefore change concentration even if mass of solute remains constant. Cause: heating often increases solubility and can expand solvent volume. Effect: measured concentrations depend on temperature control and solubility; statements of concentration must specify units and conditions when precision matters.
Key notes
Important points to keep in mind