Question

what mass of aluminum hydroxide is needed to decompose in order to produce aluminum oxide and 35 L of water at STP

Answer 1

The mass of aluminium hydroxide is 81.12 g.

Explanation:

The chemical equation for the decomposition of Aluminium hydroxide follows:

                    2 Al(OH)3 ------> Al2O3 + 3H2O

At STP:

22.4 L of volume is occupied by 1 mole of a gas.

So, 35 L of the  volume will be occupied by = (1 / 22.4) $\times$ 35 = 1.56 mol

By Stoichiometry of the reaction:

3 moles of water is produced by 2 moles of Aluminium hydroxide

So, 1.56 moles of water is produced by = (2 /3) $\times$ 1.56 = 1.04 mol.

To calculate the mass of Aluminium hydroxide, we use the equation:

         Number of moles = given mass / molar mass

Number of moles of Aluminium hydroxide = 1.04 mol

The Molar mass of Aluminium hydroxide = 78 g/mol

Putting values in above equation, we get:

           1.04 mol = mass of Aluminium hydroxide / 78

The mass of Aluminium hydroxide needed is 81.12 grams.