Input interpretation
potassium selenide | molar mass
Result
Find the molar mass, M, for potassium selenide: 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: K_2Se Use the chemical formula to count the number of atoms, N_i, for each element: | N_i K (potassium) | 2 Se (selenium) | 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) K (potassium) | 2 | 39.0983 Se (selenium) | 1 | 78.971 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) K (potassium) | 2 | 39.0983 | 2 × 39.0983 = 78.1966 Se (selenium) | 1 | 78.971 | 1 × 78.971 = 78.971 M = 78.1966 g/mol + 78.971 g/mol = 157.168 g/mol
Unit conversion
0.15717 kg/mol (kilograms per mole)
Comparisons
≈ ( 0.22 ≈ 1/5 ) × molar mass of fullerene ( ≈ 721 g/mol )
≈ 0.81 × molar mass of caffeine ( ≈ 194 g/mol )
≈ 2.7 × molar mass of sodium chloride ( ≈ 58 g/mol )
Corresponding quantities
Mass of a molecule m from m = M/N_A: | 2.6×10^-22 grams | 2.6×10^-25 kg (kilograms) | 157 u (unified atomic mass units) | 157 Da (daltons)
Relative molecular mass M_r from M_r = M_u/M: | 157