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.

Gallium melts near room temperature and has one of the largest  liquid  ranges of any metal, so it has found use in high temperature thermometers.

Each names a given number of objects