A compound contains 28% nitrogen and 72% of a metal by weight. Three atoms of metal combine with two atoms of nitrogen. If the atomic weight of nitrogen is 14, the atomic weight of the metal is:

Upon heating, 15.0 g of impure zinc carbonate decomposes completely to produce zinc oxide and carbon dioxide. If 5.6 g of zinc oxide is formed, calculate the percentage purity of the zinc carbonate sample. (Atomic weight: $Zn = 65.4$)

A sample of magnesium carbonate weighing 30.0 g is heated until it completely decomposes to magnesium oxide and carbon dioxide. If 12.0 g of magnesium oxide is produced, what is the percentage purity of the original magnesium carbonate sample? (Atomic weight: $Mg = 24$)

A student heats 40.0 g of a mixture containing magnesium carbonate and some inert impurities. Upon complete decomposition, 8.0 g of magnesium oxide is formed. Calculate the percentage by mass of magnesium carbonate in the original mixture. (Atomic weight: $Mg = 24$)

25.0 g of a calcium carbonate sample decomposes on heating to give carbon dioxide and 10.0 g calcium oxide. What will be the percentage purity of calcium carbonate in the sample? (Atomic weight: $Ca = 40$)

If 50.0 g of an impure sample of limestone (calcium carbonate) is heated, it decomposes to produce 14.0 g of calcium oxide and carbon dioxide. Determine the percentage of calcium carbonate in the limestone sample. (Atomic weight: $Ca = 40$)