Analytical Applications of Thermogravimetry

Therefore, the %W lost due to 1 mol of water of crystallization = (18/146) x 100 = 12.3%. If our initial sample mass was 20.00 mg, the mass loss at the first step would be 2.46 mg if there is 1 mol of water of crystallization. If the mass loss actually measured was 4.92 mg, it would mean that there were 2 mol of water of crystallization and the formula would be CaC204 2H20(s), a dihydrate. Upon further heating up to about 400°C, CO(g) is given off and the reaction that occurs is 

Finally, at even higher temperatures (about 800°C), the CaCOj formed at 400°C decomposes  

Because A and B have unique temperatures at which mass is lost, the composition of the 

We would lose 73 mg for every 100 mg of pure magnesium oxalate dihydrate we had in the mixture on heating the mixture to 500°C. Note that the decomposition of magnesium oxalate does not follow the same process as the decomposition of calcium oxalate. Calcium oxalate first forms calcium carbonate, which only loses carbon dioxide to form CaO at temperatures above 600°C. Magnesium oxalate appears to decompose directly to MgO in one step at about 500°C. The weight remaining from the magnesium oxalate is equal to 

The following data were obtained from our TGA curve  

This information reveals the chemical decomposition process occurring when materials are heated and permits identification of the formulas of the starting materials. TGA is very important in determining the upper use temperatures of materials such as polymers by identifying the temperature at which oxidative degradation occurs on heating in air. 

From Fig. 16.6 it can be determined that when pure calcium oxalate monohydrate, Ca(COO)2 H20(s), is heated, it first loses water of crystallization and forms Ca(COO)2(s). 

The fact that the compound contains only 1 mole of water of hydration can be determined from the mass loss. The reaction is  

Upon further heating up to about 400°C, CO(g) is given off and the reaction that occurs is  

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