Combustion Analysis Calculator

Combustion analysis burns a known mass of an organic compound completely in excess oxygen. The carbon in the compound converts entirely to carbon dioxide (CO2), and the hydrogen converts to water (H2O). Any oxygen present in the original sample is typically calculated by mass difference. First, the mass of carbon (m_C) is derived from the mass of CO2 using the molar mass ratio (12.0107 / 44.010). Similarly, the mass of hydrogen (m_H) is found from H2O using its respective ratio (2 * 1.00784 / 18.01528). The mass of oxygen (m_O) is then found by subtracting m_C and m_H from the total compound mass (m_comp). Finally, these masses are converted to moles to find the simplest whole-number ratio (empirical formula) and scaled using the known molecular mass to find the true molecular formula.

Imagine you have a 2.50 g sample of an unknown hydrocarbon compound undergoing combustion, yielding 7.33 g of CO2 and 1.50 g of H2O. First, calculate the mass of carbon: m_C = 7.33 * (12.0107 / 44.010) = 2.00 g. Next, calculate the mass of hydrogen: m_H = 1.50 * (2 * 1.00784 / 18.01528) = 0.168 g. Converting these masses to moles gives approximately 0.166 moles of carbon and 0.167 moles of hydrogen. Finding the simplest molar ratio yields an empirical formula of CH. If the molecular mass is determined to be 78.11 g/mol, the empirical mass is 13.02 g/mol, giving a multiplier of 78.11 / 13.02 = 6. This scales the empirical formula up to the final molecular formula of C6H6 (benzene).

Always double-check your initial sample mass and the masses of the collected gaseous products, as even minor weighing discrepancies can skew the resulting empirical formula. Ensure your molar mass values match standard periodic table guidelines to maintain precision through every mathematical step. When dealing with compounds containing oxygen, remember that oxygen mass is always found via subtraction rather than direct absorption collection.