Input interpretation
chrome potash alum | molar mass
Result
Find the molar mass, M, for chrome potash alum: 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: CrKO_8S_2 Use the chemical formula to count the number of atoms, N_i, for each element: | N_i Cr (chromium) | 1 K (potassium) | 1 O (oxygen) | 8 S (sulfur) | 2 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) Cr (chromium) | 1 | 51.9961 K (potassium) | 1 | 39.0983 O (oxygen) | 8 | 15.999 S (sulfur) | 2 | 32.06 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) Cr (chromium) | 1 | 51.9961 | 1 × 51.9961 = 51.9961 K (potassium) | 1 | 39.0983 | 1 × 39.0983 = 39.0983 O (oxygen) | 8 | 15.999 | 8 × 15.999 = 127.992 S (sulfur) | 2 | 32.06 | 2 × 32.06 = 64.12 M = 51.9961 g/mol + 39.0983 g/mol + 127.992 g/mol + 64.12 g/mol = 283.21 g/mol
Unit conversion
0.28321 kg/mol (kilograms per mole)
Comparisons
≈ 0.39 × molar mass of fullerene ( ≈ 721 g/mol )
≈ 1.5 × molar mass of caffeine ( ≈ 194 g/mol )
≈ 4.8 × molar mass of sodium chloride ( ≈ 58 g/mol )
Corresponding quantities
Mass of a molecule m from m = M/N_A: | 4.7×10^-22 grams | 4.7×10^-25 kg (kilograms) | 283 u (unified atomic mass units) | 283 Da (daltons)
Relative molecular mass M_r from M_r = M_u/M: | 283