Precipitation gravimetry and gravimetric factors
In precipitation gravimetry, a measured precipitate mass is converted to analyte mass using the analyte-to-precipitate mass fraction established by chemical stoichiometry.
The entered coefficients must describe the balanced relationship between analyte and weighed precipitate. Chemical formulas are used only to calculate molar masses; the calculator does not balance the reaction.
How to calculate gravimetric mass percent
- Enter masses: Use sample and dry precipitate masses in grams.
- Enter formulas: Use element symbols, subscripts as digits, and parentheses where needed; omit charges and hydrate dots.
- Enter stoichiometry: Provide positive coefficients from the balanced analyte-to-precipitate relationship.
- Calculate and review: Check factor, analyte mass, and percent against chemical plausibility and quality controls.
Formula and variables
The gravimetric factor gF converts weighed precipitate mass to the corresponding analyte mass.
gF = (MAνA)/(MPνP); w% = (mP × gF / msample) × 100- MA — Analyte molar mass
- Calculated from the analyte formula (g/mol)
- MP — Precipitate molar mass
- Calculated from the weighed precipitate formula (g/mol)
- νA, νP — Stoichiometric numbers
- Balanced analyte and precipitate relationship (dimensionless)
- mP — Precipitate mass
- Dry weighed precipitate (g)
- msample — Sample mass
- Original sample mass (g)
Phosphorus weighed as magnesium pyrophosphate
A 1.5 g sample yields 0.25 g Mg₂P₂O₇; one mole of precipitate contains two moles of P.
- Masses
- 1.5 g sample; 0.25 g precipitate
- Formulas and coefficients
- 2 P per 1 Mg₂P₂O₇
- gF = (2 × M(P)) / M(Mg₂P₂O₇) ≈ 0.27835
- w% = 0.25 × 0.27835 / 1.5 × 100
Result: The phosphorus mass percentage is approximately 4.64%.
The estimated sample contains about 0.0696 g of phosphorus under the assumed reaction and recovery.
Understanding your results
Chemical validity comes before arithmetic
A precise numeric result can still be biased by an invalid precipitate composition or incomplete laboratory process.
- The precipitate must have the assumed stoichiometric composition.
- Incomplete precipitation causes low recovery.
- Coprecipitation, contamination, or retained moisture can cause high mass.
- Blank correction and replicate uncertainty are not included.
Assumptions
- The precipitate is pure, dry, stable, and of the entered formula.
- Stoichiometric coefficients come from a valid balanced reaction.
- Sample and precipitate masses use the same mass unit.
Limitations
- Does not balance reactions or model solubility, recovery, blanks, impurities, or measurement uncertainty.
- Formula parser does not support charges, hydrate-dot notation, isotopes, or nonstoichiometric solids.
- Atomic weights are conventional tabulated values and may not match isotope-specific work.
Common mistakes
- Using formula subscripts as reaction coefficients.
- Reversing analyte and precipitate stoichiometric numbers.
- Weighing a precipitate before complete drying or ignition.
- Assuming precipitation is quantitative without validation.
Practical use cases
Analytical chemistry coursework
Check factor and mass-fraction calculations from a balanced precipitation reaction.
Laboratory calculation review
Verify arithmetic after appropriate method blanks and quality controls are established separately.
Frequently asked questions
What is a gravimetric factor?
It is the mass fraction of analyte represented by the weighed precipitate for the specified stoichiometric relationship.
Does the calculator balance the reaction?
No. You must enter coefficients from a correctly balanced chemical relationship.
Can the mass percent exceed 100%?
A result above 100% usually signals inconsistent inputs, formulas, stoichiometry, contamination, or an inapplicable method; the arithmetic alone cannot diagnose the cause.
Sources and review
- Gravimetric Factor — IUPAC Compendium of Chemical Terminology. Accessed 2026-07-13.
Reviewed 2026-07-13.