Input interpretation
tricalcium orthoarsenate | molar mass
Result
Find the molar mass, M, for tricalcium orthoarsenate: 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: As_2Ca_3O_8 Use the chemical formula, As_2Ca_3O_8, to count the number of atoms, N_i, for each element: | N_i As (arsenic) | 2 Ca (calcium) | 3 O (oxygen) | 8 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) As (arsenic) | 2 | 74.921595 Ca (calcium) | 3 | 40.078 O (oxygen) | 8 | 15.999 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) As (arsenic) | 2 | 74.921595 | 2 × 74.921595 = 149.843190 Ca (calcium) | 3 | 40.078 | 3 × 40.078 = 120.234 O (oxygen) | 8 | 15.999 | 8 × 15.999 = 127.992 M = 149.843190 g/mol + 120.234 g/mol + 127.992 g/mol = 398.069 g/mol
Unit conversion
0.39807 kg/mol (kilograms per mole)
Comparisons
≈ 0.55 × molar mass of fullerene ( ≈ 721 g/mol )
≈ 2 × molar mass of caffeine ( ≈ 194 g/mol )
≈ 6.8 × molar mass of sodium chloride ( ≈ 58 g/mol )
Corresponding quantities
Mass of a molecule m from m = M/N_A: | 6.6×10^-22 grams | 6.6×10^-25 kg (kilograms) | 398 u (unified atomic mass units) | 398 Da (daltons)
Relative molecular mass M_r from M_r = M_u/M: | 398