2. Gravimetric Analysis
Gravimetric methods is thequantitative methods that are based on determiningthe mass of a purecompound to which the analyte is chemically
related.
Gravimetric analysis is a technique throughwhich theamount of ananalyte(the ion being analyzed) canbe determined throughthe
measurement of mass. Gravimetric analyses depend on comparing the masses of two compounds containingthe analyte.
3. Gravimetric Analysis
Theprinciple behind gravimetric analysis is that the mass of an ion ina pure compound can be determinedand then used to find the mass
percent of thesame ion in a knownquantity of animpurecompound. In order for the analysis to be accurate,certain conditions must be met: -
Theion being analyzedmust becompletely precipitated.
Theprecipitate must bea pure compound.
Theprecipitate must beeasily filtered.
4. Gravimetric Analysis
Precipitationgravimetry:Theanalyteis separated from a solution of the sample as a precipitate and is converted to a compound of known
composition that can beweighed.
Theanalyteis converted to a sparingly soluble precipitate that is then filtered, washed freeof impuritiesand converted to a product of
knowncomposition by suitable heat treatment and weighed
5. Gravimetric Analysis
Ex. for determining the [Ca2+] in water:
2NH3(aq) + H2C2O4(aq) → 2NH4(aq) + C2O4(aq)
Ca2+ + C2O4(aq) → CaC2O4(s)
filtered, dried, ignited
Heat
CaC2O4(s) → CaO(s) + CO(g) + CO2(g)
After cooling, the precipitate is weighed and the mass is determined.
6. Gravimetric Analysis
Volatilization gravimetry: Theanalyteis separated from other constituents of a sample by converting it to a gas of knownchemicalcomposition
that can beweighed.
A second approach to gravimetryis to thermally or chemicallydecompose the sample and measure the resulting changein its mass. Alternatively,
wecan trap and weigh a volatile decomposition product. Because the release of a volatile species is an essential part of these methods, weclassify
them collectively as volatilization gravimetric methods of analysis.
8. Gravimetric Analysis
Thermogravimetry:
One method for determining the products of a thermal decomposition is to monitor the sample’s mass as a function of temperature, a process
called thermogravimetry. A typical thermogram shows change in mass in each “step” which basically represents the loss of a volatile product.
A thermogram can be used to identify a compound’s decomposition reactions.
