The mass of 0.3253 mol of a compound with the formula mbr4, in which m is a metallic element, is 171.4 g. what is the identity of the metal

Lead (Pb) Let's figure out how many moles of the unknown element there is and what it's atomic weight is. We have 0.3253 mol of mBr4 which has a mass of 171.4 g. Since there's 4 bromine atoms per molecule, that means we have 4 * 0.3253 = 1.3012 moles of bromine. The atomic weight of bromine is 79.904, so 1.3012 mol * 79.904 g/mol = 103.9711 g So now subtract the known mass of bromine from the mass of the unknown substance. 171.4g - 103.9711g = 67.42892 g Now divide that by the number of moles we have of that metal to determine its atomic weight 67.42892 g / 0.3253 mol = 207.2822 g/mol Now look at the periodic table to see if there's any metals with an atomic weight close to 207.2822 g/mol The closest match is for Lead (Pb) with an atomic weight of 207.2. Additionally, it's in the same column as Carbon so Lead has 4 valance electrons. And Bromine wants to grab one electron so you'd expect lead to combine with 4 bromine atoms. Which this compound does. So the evidence indicates that the unknown metal is Lead.