Input interpretation
lithium amide | molar mass
Result
Find the molar mass, M, for lithium amide: 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: LiNH_2 Use the chemical formula to count the number of atoms, N_i, for each element: | N_i H (hydrogen) | 2 Li (lithium) | 1 N (nitrogen) | 1 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) H (hydrogen) | 2 | 1.008 Li (lithium) | 1 | 6.94 N (nitrogen) | 1 | 14.007 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) H (hydrogen) | 2 | 1.008 | 2 × 1.008 = 2.016 Li (lithium) | 1 | 6.94 | 1 × 6.94 = 6.94 N (nitrogen) | 1 | 14.007 | 1 × 14.007 = 14.007 M = 2.016 g/mol + 6.94 g/mol + 14.007 g/mol = 22.96 g/mol
Unit conversion
0.023 kg/mol (kilograms per mole)
Comparisons
≈ ( 0.12 ≈ 1/8 ) × molar mass of caffeine ( ≈ 194 g/mol )
≈ 0.39 × molar mass of sodium chloride ( ≈ 58 g/mol )
≈ 1.3 × molar mass of water ( ≈ 18 g/mol )
Corresponding quantities
Mass of a molecule m from m = M/N_A: | 3.8×10^-23 grams | 3.8×10^-26 kg (kilograms) | 23 u (unified atomic mass units) | 23 Da (daltons)
Relative molecular mass M_r from M_r = M_u/M: | 23