Thermal decomposition of 7.2 g of metal hydroxide resulted in 5.175 g of metal oxide.

Thermal decomposition of 7.2 g of metal hydroxide resulted in 5.175 g of metal oxide. Determine the formula for the metal hydroxide.

Let us write down the equations of possible reactions of metal decomposition, taking into account the valence:

Me (OH) 2 = MeO + H2O.

2Me (OH) 3 = Me2O3 + 3H2O.

Let’s make a proportion for the first reaction. We denote Me by x.

If 5.75 g of oxide is formed from 7.2 g of hydroxide, then MeO (x + 16) g is formed from Me (OH) 2 (x + 34) g.

Find x:

x = 55. The molar mass corresponds to manganese – Mn (OH) 2.

The proportion for the second reaction will have no solution.
7.2 g – 5.75 g
(2x + 51) g – (2x + 48) g.