Input interpretation
ethylene | molar mass
Result
Find the molar mass, M, for ethylene: M = sum _iN_im_i Plan: • Write the chemical formula and gather atomic masses from the periodic table. • Determine values for N_i and m_i using these items. • Finally, compute the mass. Write the chemical formula: CH_2=CH_2 Use the chemical formula to count the number of atoms, N_i, for each element: | N_i C (carbon) | 2 H (hydrogen) | 4 Look up the atomic mass, m_i, in g·mol^(-1) for each element in the periodic table: | N_i | m_i/g·mol^(-1) C (carbon) | 2 | 12.011 H (hydrogen) | 4 | 1.008 Multiply N_i by m_i to compute the mass for each element. Then sum those values to compute the molar mass, M: Answer: | | | N_i | m_i/g·mol^(-1) | mass/g·mol^(-1) C (carbon) | 2 | 12.011 | 2 × 12.011 = 24.022 H (hydrogen) | 4 | 1.008 | 4 × 1.008 = 4.032 M = 24.022 g/mol + 4.032 g/mol = 28.054 g/mol
Unit conversion
0.028054 kg/mol (kilograms per mole)
Comparisons
≈ ( 0.14 ≈ 1/7 ) × molar mass of caffeine ( ≈ 194 g/mol )
≈ 0.48 × molar mass of sodium chloride ( ≈ 58 g/mol )
≈ 1.6 × molar mass of water ( ≈ 18 g/mol )
Corresponding quantities
Mass of a molecule m from m = M/N_A: | 4.7×10^-23 grams | 4.7×10^-26 kg (kilograms) | 28 u (unified atomic mass units) | 28 Da (daltons)
Relative molecular mass M_r from M_r = M_u/M: | 28