7.5 g of aluminum reacts with an excess of oxygen how many grams of aluminum oxide are produced?

14.2 grams

Let's start by looking up the atomic weights of aluminum and oxygen. Atomic weight aluminum = 26.981539

Atomic weight oxygen = 15.999

Moles Al = 7.5 g / 26.981539 g/mol = 0.277967836

The formula for aluminum oxide is Al2O3, so for every 2 moles of Al, 3 moles of O is required. So let's calculate the number of moles of O we need and from that the mass.

0.277967836 mol / 2 * 3 = 0.416951754 mol

Mass O2 = 0.416951754 * 15.999 = 6.670811105

The mass of aluminum oxide is simply the mass of aluminum plus the mass of oxygen. So:

7.5 g + 6.670811105 g = 14.17081111 g

Rounding to 1 decimal place gives 14.2 g.