What mass of water is formed during the decomposition of 30.9 g of chromium (III) hydroxide?

2Cr (OH) 3 = Cr2O3 + 3H2O.
1) Find the molar mass of chromium hydroxide according to the periodic table: 52 + 48 + 3 = 103.
2) Find the amount of chromium hydroxide substance. To do this, divide the mass of the hydroxide by its molar mass: 30.9 / 103 = 0.3 mol.
3) According to the reaction equation, there are three moles of water for two moles of chromium hydroxide. This means that the amount of water substance is: 2 * 0.3 / 3 = 0.2 mol.
4) Molar mass of water: 1 * 2 + 16 = 18.
5) The mass of water: 0.2 * 18 = 3.6 g is the answer.



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