The most abundant metal in Earth's crust is aluminum, found mostly in the form of clays. There are no economical routes for extracting aluminum from clay. However, bauxite ore, impure hydrated aluminum oxide, is found in hot, humid regions, such as Australia, Guinea, and Brazil, and it can be purified and refined to make the metal. After the first purification step, hydrated aluminum oxide (Al₂O₃ . xH₂O) is obtained. When 100.0 g of this solid were heated, and the water driven off, 65.36 g of Al₂O₃ remained. How many water molecules (x in the molecular formula) were there in the hydrate?

Question

Quizplus · Accepted Answer

First, calculate the mass of water lost: 100.0 g - 65.36 g = 34.64 g Then, use the molar mass of water (18.015 g/mol) to convert this mass to moles: 34.64 g / 18.015 g/mol = 1.922 mol The ratio of moles of water to moles of Al₂O₃ in the formula is x:1. So, the answer is closest to the whole number that equals x. 1.922 is closest to 2, so x = 2, and the answer is (B) 2.

The Most Abundant Metal in Earth's Crust Is Aluminum, Found