Input interpretation
ethane | molecular mass
Result
Find the molecular mass, m, for ethane: 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_3CH_3 Use the chemical formula to count the number of atoms, N_i, for each element: | N_i C (carbon) | 2 H (hydrogen) | 6 Look up the atomic mass, m_i, in unified atomic mass units, u, for each element in the periodic table: | N_i | m_i/u C (carbon) | 2 | 12.011 H (hydrogen) | 6 | 1.008 Multiply N_i by m_i to compute the mass for each element. Then sum those values to compute the molecular mass, m: Answer: | | | N_i | m_i/u | mass/u C (carbon) | 2 | 12.011 | 2 × 12.011 = 24.022 H (hydrogen) | 6 | 1.008 | 6 × 1.008 = 6.048 m = 24.022 u + 6.048 u = 30.070 u
Unit conversions
30.07 Da (daltons)
0.03007 kDa (kilodaltons)
4.993×10^-23 grams
4.993×10^-26 kg (kilograms)
30.071 chemical atomic mass units (unit officially deprecated)
30.08 physical atomic mass units (unit officially deprecated)
Comparisons as mass of molecule
≈ ( 0.15 ≈ 1/6 ) × molecular mass of caffeine ( ≈ 194 u )
≈ 0.51 × molecular mass of sodium chloride ( ≈ 58 u )
≈ 1.7 × molecular mass of water ( ≈ 18 u )
Corresponding quantities
Relative atomic mass A_r from A_r = m_aN_A/M_u: | 30
Molar mass M from M = m_aN_A: | 30 g/mol (grams per mole)
Relative molecular mass M_r from M_r = m_mN_A/M_u: | 30
Molar mass M from M = m_mN_A: | 30 g/mol (grams per mole)