Input interpretation
chromium(III) oxide | molar mass
Result
Find the molar mass, M, for chromium(III) oxide: 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: Cr_2O_3 Use the chemical formula to count the number of atoms, N_i, for each element: | number of atoms Cr (chromium) | 2 O (oxygen) | 3 Look up the atomic mass, m_i, in g·mol^(-1) for each element in the periodic table: | number of atoms | atomic mass/g·mol^(-1) Cr (chromium) | 2 | 51.9961 O (oxygen) | 3 | 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: | | | number of atoms | atomic mass/g·mol^(-1) | mass/g·mol^(-1) Cr (chromium) | 2 | 51.9961 | 2 × 51.9961 = 103.9922 O (oxygen) | 3 | 15.999 | 3 × 15.999 = 47.997 M = 103.9922 g/mol + 47.997 g/mol = 151.989 g/mol
Unit conversion
0.15199 kg/mol (kilograms per mole)
Comparisons
≈ ( 0.21 ≈ 1/5 ) × molar mass of fullerene (≈ 721 g/mol )
≈ 0.78 × molar mass of caffeine (≈ 194 g/mol )
≈ 2.6 × molar mass of sodium chloride (≈ 58 g/mol )
Corresponding quantities
Mass of a molecule m from m = M/N_A: | 2.5×10^-22 grams | 2.5×10^-25 kg (kilograms) | 152 u (unified atomic mass units) | 152 Da (daltons)
Relative molecular mass M_r from M_r = M_u/M: | 152