Final answer:
Combustion analysis can be used to find the molecular formula of a sample of a mixture containing an unknown hydrocarbon and nitrogen dioxide. By analyzing the masses of NO2 and H2O produced from the sample, the number of moles of each element is calculated to determine the compound's empirical formula. The molecular formula is then derived using the known molar mass.
Step-by-step explanation:
To determine the molecular formula of a sample of a mixture containing an unknown hydrocarbon and some nitrogen dioxide, one would typically use a process known as combustion analysis. Combustion analysis involves burning the hydrocarbon in oxygen, measuring the resulting carbon dioxide (CO2) and water (H2O), and using stoichiometry to determine the amounts of carbon and hydrogen in the original sample.
In the given question, a 3.5-gram sample decomposes to produce 4.00 grams of NO2 and 7.00 grams of H2O. The resulting molar mass of the compound is 78.5 g/mol. To find the molecular formula, one would first need to calculate the number of moles of each element in the sample based on these products. For example, the amount of hydrogen can be found by dividing the mass of water (which contains hydrogen) by the molar mass of water and then by the number of hydrogen atoms per molecule of water.
Similarly, the nitrogen content can be estimated by considering the molar mass of NO2 to calculate the moles of nitrogen in the 4.00 grams of nitrogen dioxide produced. Once the moles of each element are known, the empirical formula of the compound is determined, and this is then used to find the molecular formula by comparing the empirical formula mass to the given molar mass, 78.5 g/mol.