Thermogravimetry which is one form of volatilization gravimetry

Thermogravimetry, which is one form of volatilization gravimetry, the sample’s mass is continuously monitored while the applied temperature is slowly increased. This requirement is rarely a problem for organic compounds in which volatilization is usually accomplished by combustion and the products are gases such as CO 2, H 2 O, and N.

Thermal Gravimetric Analysis (TGA) gave information about: - • Evaluate thermal decomposition and stability of materials — Polymers, resins, rubbers, explosives • Information on bulk composition of compounds — Thermal oxidation, heat resistance — Residual water or solvents — Compositional analysis — Ash content in a sample — Quantity of inorganic filler in a polymer

Thermograrns for some common polymeric materials. PVC = polyvinyl chloride PMMA= poly methyl methacrylate LDPE= low density po 1 y ethy 1 ene PTFE= Po 1 y tetrafluoroethylene P 1 = aromatic Poly pyromellitimide

Ex. : - The change in mass for a sample of calcium oxalate monohydrate, Ca. C 2 O 4. H 2 O. The original sample weighed 24. 60 mg and was heated from room temperature to 1000 °C at a rate of 5 °C min. The following changes in mass and corresponding temperature ranges were observed: Loss of 3. 03 mg from 100– 250 °C Loss of 4. 72 mg from 400– 500 °C Loss of 7. 41 mg from 700– 850 °C Determine the identities of the volatilization products and the solid residue at each step of thermal decomposition.

H 2 O, C 7 H 3 O 6, C 6 H 4 , CO 2 are consecutively lost.

Ex. : - A 101. 3 -mg sample of an organic compound containing chlorine is combusted in pure O 2 and the volatile gases collected in absorbent traps. The trap for CO 2 increases in mass by 167. 6 mg and the trap for H 2 O show a 13. 7 -mg increase. A second sample of 121. 8 mg is treated with concentrated HNO 3 producing Cl 2, which subsequently reacts with Ag+, forming 262. 7 mg of Ag. Cl. Determine the compound’s composition, as well as its empirical formula

Exercise 1 Naturally occurring gypsum is a hydrated salt of calcium sulphate(Ca. SO 4. XH 2 O). A 67. 5 gm sample of gypsum is heated in a crucible until a constant mass is obtained. The mass of anhydrous salt (Ca. SO 4) was found to be 53. 4 gm, calculate : a- The percent by mass of water in the gypsum sample (hydrated salt). b-What is the formula of gypsum ? Exercise 2 A 695 gm of Cu. SO 4. XH 2 O is heated in a crucible until a constant mass is obtained and the mass of the anhydrous salt (Cu. SO 4) was found to be 444 gm, if you know that the F. W. of H 2 O = 18 gm/mol and the F. W. of anhydrous salt Cu. SO 4 = 159. 54 gm/mol, calculate a- The percent by mass of water in the hydrated salt. b-What is the formula of hydrated salt ?