Input interpretation
hydrogen bromide | molecular mass
Result
Find the molecular mass, m, for hydrogen bromide: 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: HBr Use the chemical formula to count the number of atoms, N_i, for each element: | N_i Br (bromine) | 1 H (hydrogen) | 1 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 Br (bromine) | 1 | 79.904 H (hydrogen) | 1 | 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 Br (bromine) | 1 | 79.904 | 1 × 79.904 = 79.904 H (hydrogen) | 1 | 1.008 | 1 × 1.008 = 1.008 m = 79.904 u + 1.008 u = 80.912 u
Unit conversions
80.912 Da (daltons)
0.080912 kDa (kilodaltons)
1.3436×10^-22 grams
1.3436×10^-25 kg (kilograms)
80.915 chemical atomic mass units (unit officially deprecated)
80.938 physical atomic mass units (unit officially deprecated)
Comparisons as mass of molecule
≈ ( 0.11 ≈ 1/9 ) × molecular mass of fullerene ( ≈ 721 u )
≈ 0.42 × molecular mass of caffeine ( ≈ 194 u )
≈ 1.4 × molecular mass of sodium chloride ( ≈ 58 u )
Corresponding quantities
Relative atomic mass A_r from A_r = m_aN_A/M_u: | 81
Molar mass M from M = m_aN_A: | 81 g/mol (grams per mole)
Relative molecular mass M_r from M_r = m_mN_A/M_u: | 81
Molar mass M from M = m_mN_A: | 81 g/mol (grams per mole)