When aluminum metal is heated with an element from group VIA of the periodic table, an ionic compound forms. When the experiment is performed with an unknown croup VIA element, the product is 18.56% Al by mass. What is the formula of the compound and what is its name?
Let's say you have l00 grams of this compound, so inside the compound would be l8.56 grams of Aluminum and the remaining. 81.44 grams of the second element. Elements in group 6A have 6 electrons in their outer shell and an oxidation # of -2 and the formula for the compound would be Al2X3. a 2mole Al to 3 mole X ratio. The compound would have the atom ratio of Al2X3 derived from the valences of +3 and -2. So the two aluminum atoms in the compound would be providing a total mass of l8.56 grams and the three atoms of X would be providing the remaining mass of 81.44 g so we have the ratio. l8.56 g Al/ 2 Al moles = 81.44 grams element X/ 3 moles X The mass ratio between these two elements is 8l.44 over l8.56 or 4.38 to l The atomic wt. total for 2 aluminum atoms is 54 so the atomic wtl total for three atoms of element X should be 4.38 times 54 which is 236.9 Now if we divide 236.9 by three atoms of X in the compound we get an atomic wt. of 78.9 which corresponds to Selenium So the compound is Al2Se3. This was a challenging problem, congratulations to your chem teacher.!!!
