How to do this moles question
An oxide of Y has a formula YO. When 2.16g of this oxide is heated strongly. it decomposes completely to give 120 cm^3 of oxygen measured at room temperature and pressure
calculate relative atomic mass of Y
name the oxide of Y
When the YO decomposes, it will produce one mole of Y for every mole of YO and 1/2 mole of O2 for every mole of YO.
Since there are 22,400 cc of a gas in one mole, then in this case there are 120/22,400 moles of oxygen produced. This is equal to .0053 moles of oxygen. That means you started with .0107 moles of YO.
Now .0053 moles of oxygen = .0848 g which leaves 2.16 - .0848 or 2.0752 g of Y. Since this is equal to .01068 moles of Y, if you divide the mass by the number of moles you get the molar mass of the element. 2.0752/.01068 = 194.3 g. Looking at the periodic table, the element closest in mass to this is platinum at 195.2 g/mole.
Therefore, the name of the oxide would be platinum oxide.