Final answer:
The compound with a molar mass of 30.0g, 20.0% hydrogen and 80.0% carbon dioxide has a molecular formula of CH6O2, derived from the mass percentage composition and the molar masses of hydrogen and carbon dioxide.
Step-by-step explanation:
To determine the compound's molecular formula with a molar mass of 30.0g and a percentage composition of 20.0% hydrogen and 80.0% carbon dioxide, start by calculating the grams of each element in one mole of the compound. Since the percentages given are mass percentages, 20% of the molar mass (30.0g) is hydrogen, which is 6.0g, and 80% is carbon dioxide, which is 24.0g.
The molar mass of hydrogen (H) is 1.008 g/mol, and the molar mass of carbon dioxide (CO2) is 44.01 g/mol. To find the number of moles, divide the mass of each element by its molar mass. For hydrogen: 6.0g ÷ 1.008g/mol = 5.952 moles. For carbon dioxide: 24.0g ÷ 44.01g/mol = 0.545 moles.
The next step is to obtain the simplest whole number ratio. As carbon dioxide consists of one carbon atom and two oxygen atoms, the amount of moles of carbon will be the same as the moles of carbon dioxide, and the moles of oxygen will be twice this value. For hydrogen, the resulting ratio from the moles calculated is approximately 6:1 hydrogen to carbon dioxide. To get integer numbers, this ratio can be simplified to 6:1, indicating that for every mole of carbon dioxide, there are about 6 moles of hydrogen.
The chemical formula of carbon dioxide is CO2, so including the hydrogen, the empirical formula becomes CH6O2. This empirical formula has a mass of (1 × 12.01) + (6 × 1.008) + (2 × 16.00) = 30.05g/mol approximately, which is very close to the given molar mass of 30.0g. Therefore, the molecular formula of the compound is also CH6O2.