From thermogravimetric analysis of a 0.7g desiccated sample you find that 5.2% of mass is lost before 150C. You also find that 26.5% of the mass is lost between 150 and 500C. Finally, 23.4% of the mass is lost near 840C. By other means, you know this soil is devoid of Si but high in Ca and Fe. What are the likely phases present? Be as specific as you can. For example, metal oxide is bad. Giving the exact stoichiometry for the most likely metal oxide is good.

Check below for answers and explanations

Explanation:

The components of the soil are organic matter, minerals, calcium and iron.

Let us find the masses of the individual components

Mass of the dessicated sample, M = 0.7 g

For the 5.2% loss in mass:

Mass of organic matter below 150°C = 5.2% of 0.7g

Mass of organic matter below 150°C = 0.052*0.7 = 0.0364 g

Mass of minerals below 500°C = 26.5% of 0.7g

Mass of minerals below 500°C = 0.265 * 0.7

Mass of minerals below 500°C = 0.1855 g

Mass of calcium below 840°C = 23.5% of 0.7

Mass of calcium below 840°C = 0.235 * 0.7

Mass of calcium below 840°C = 0.1645 g

Note: The melting point of calcium is 840°C

The mass of Iron = 0.7 - (0.0364 + 0.1855 + 0.1645)

Mass of iron = 0.3136 g

the answer would be c