TGA Mass Loss Calculator
Convert a TGA thermogram into per-step mass loss, final residue and lost-group molar mass.
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What it does
Thermogravimetric analysis (TGA) records how a sample's mass changes as temperature rises, but a raw thermogram is just a falling curve. This calculator turns that curve into a structured table: the percentage lost in each step, the remaining mass after every step, the total mass lost, and the final residue. It also estimates the molar mass of whatever leaves in each step when you supply the residue formula. Materials scientists, inorganic chemists and battery engineers use it to check hydration, decomposition and the stoichiometry of decomposition products without hand arithmetic.
How it works
The calculator works only with percentages, so no absolute mass is needed. Each step loss is the drop in remaining mass from the previous step to the current one: step loss % = start % - end %. The first step is implicitly measured from 100%. Total loss % = 100 - final residue %. If you enter a residue formula, the molar mass M of that residue is parsed and each step's lost mass is scaled to one mole of residue: lost mass per mole = (step loss % / final residue %) x M, in g/mol. Temperatures are labels only and do not enter the math.
Worked example
Calcium oxalate monohydrate, CaC2O4·H2O, decomposes in three clean steps. From 100% it falls to about 87.6% near 150 C as one H2O (18.0 g/mol) leaves, to about 68.5% near 450 C as CO (28.0 g/mol) leaves, and to about 38.4% near 800 C as CO2 (44.0 g/mol) leaves, ending as CaO (56.1 g/mol). Taking CaO as the residue, the first step's lost mass per mole is (12.4 / 38.4) x 56.1 = about 18.1 g/mol, matching the 18.0 g/mol of water and confirming the assignment.
When to use it
Use this tool to interpret dehydration, decomposition and oxidation steps, to verify a hydrate's water count, or to estimate the formula of an unknown residue from its mass fraction. A frequent check is whether the per-step lost mass matches a plausible group (H2O, CO2, a ligand). The main pitfalls are that step assignment depends on atmosphere and heating rate: a step seen in air may be oxidation, not simple dehydration, and fast heating can merge or shift steps. Always read the temperature as a guide, not a proof, and confirm with an MS or XRD of the residue.
FAQ
- What does TGA measure and what units?
- TGA measures mass loss as a function of temperature, reported here as remaining mass percent from an initial 100%. Each step loss is the percent drop between two plateaus, and total loss is 100 minus the final residue. If you give the residue formula, the tool also reports lost mass per mole of residue in g/mol, which helps assign the leaving group without weighing the absolute sample mass.
- How is the lost mass per mole calculated?
- The tool parses the residue formula to get its molar mass M, then scales each step loss to one mole of that residue: lost mass per mole = (step loss % / final residue %) x M. For CaC2O4·H2O ending as CaO (56.1 g/mol), a first step loss of 12.4% over a final residue of 38.4% gives (12.4 / 38.4) x 56.1 = about 18.1 g/mol, matching water. No absolute mass is needed, only percentages.
- Why does step assignment depend on atmosphere?
- The same mass drop can mean different chemistry in different gases. In nitrogen a 44 g/mol step is usually CO2 loss, but in air the same sample may oxidize, so the residue is an oxide rather than the carbonate and the steps shift. Heating rate matters too: at 10 C/min versus 20 C/min a dehydration and decomposition can merge or separate. Always state the gas and rate, and confirm the residue by XRD or MS.
- What is a typical TGA heating rate and range?
- Most routine TGA runs heat from room temperature to about 800-1000 C at 10 C/min in flowing nitrogen or air, which keeps steps resolved without excessive run time. Hydration and ligand loss often appear below 300 C, carbonate breakdown near 400-600 C, and oxide formation above 600 C. Faster rates up to 20 C/min save time but can blur close steps, so 10 C/min is the common default for assignment work.