Input interpretation
scandium sulfide | relative molecular mass
Result
Find the relative molecular mass, M_r, for scandium sulfide: M_r = sum _iN_im_i/m_u 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: Sc_2S_3 Use the chemical formula to count the number of atoms, N_i, for each element: | N_i S (sulfur) | 3 Sc (scandium) | 2 Look up the atomic mass, m_i, in unified atomic mass units, u, for each element in the periodic table. Since m_i is divided by the atomic mass constant, m_u, the result is a unitless relative atomic mass: | N_i | m_i/m_u S (sulfur) | 3 | 32.06 Sc (scandium) | 2 | 44.955908 Multiply N_i by m_i/m_u to compute the relative mass for each element. Then sum those values to compute the relative molecular mass, M_r: Answer: | | | N_i | m_i/m_u | relative mass S (sulfur) | 3 | 32.06 | 3 × 32.06 = 96.18 Sc (scandium) | 2 | 44.955908 | 2 × 44.955908 = 89.911816 M_r = 96.18 + 89.911816 = 186.09
Comparisons
≈ 0.26 × relative molecular mass of fullerene ( ≈ 721 )
≈ 0.96 × relative molecular mass of caffeine ( ≈ 194 )
≈ 3.2 × relative molecular mass of sodium chloride ( ≈ 58 )
Corresponding quantities
Molar mass M from M = M_uM_r: | 186 g/mol (grams per mole)
Molecular mass m from m = M_rM_u/N_A: | 3.1×10^-22 grams | 3.1×10^-25 kg (kilograms)