Calcium and Magnesium carbonates occur together in the mineral dolomite. Suppose you heat a sample of the mineral to obtain the oxides, CaO and MgO and then treat the oxide sample with hydrochloric axid. If 7.695g of the oxide sample requires 125mL of 2.55M HCl,CaO(s) + 2HCl(aq) ---gt; CaCl2(aq) + H2O(l)MgO(s) + 2HCl(aq) ---gt; MgCl2 (aq) + H2O(l)what is the weight percent of each oxide (CaO and MgO) in the sample?
Let's find the AVAILABLE moles of HCl, which is 0.125 L x 2.55M 0.32 moles (appx). Since both Ca and Mg are +2 anions, the stoichiometry shows that 7.695 g of mixed oxide represents 0.16 MOLES of mixed oxides. Now you can mole-balance to find the moles of each element's oxide. Let X be the CaO moles and 0.16-X is the MgO moles. The mole wt of CaO is about 56; that of MgO, about 40. Then the balance becomes: 56X + 40(0.16-X) 7.695 g or 16X 1.295 g. Solve for X (about 0.08) and 0.16-X is about 0.08. In moles, the oxides are roughly 50/50. Multiply each mole by the mole wt of the appropriate oxide to get weights , and then mass percent of each weight of each x 100/7.695.
