Input interpretation
![aluminum oxide | relative molecular mass](../image_source/4e8439cc6eb6a5d6efc1a34e6f3705f5.png)
aluminum oxide | relative molecular mass
Result
![Find the relative molecular mass, M_r, for aluminum oxide: 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: Al_2O_3 Use the chemical formula, Al_2O_3, to count the number of atoms, N_i, for each element: | N_i Al (aluminum) | 2 O (oxygen) | 3 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 Al (aluminum) | 2 | 26.9815385 O (oxygen) | 3 | 15.999 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 Al (aluminum) | 2 | 26.9815385 | 2 × 26.9815385 = 53.9630770 O (oxygen) | 3 | 15.999 | 3 × 15.999 = 47.997 M_r = 53.9630770 + 47.997 = 101.960](../image_source/9a13f3549678cc60120bed5ff4ad4466.png)
Find the relative molecular mass, M_r, for aluminum oxide: 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: Al_2O_3 Use the chemical formula, Al_2O_3, to count the number of atoms, N_i, for each element: | N_i Al (aluminum) | 2 O (oxygen) | 3 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 Al (aluminum) | 2 | 26.9815385 O (oxygen) | 3 | 15.999 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 Al (aluminum) | 2 | 26.9815385 | 2 × 26.9815385 = 53.9630770 O (oxygen) | 3 | 15.999 | 3 × 15.999 = 47.997 M_r = 53.9630770 + 47.997 = 101.960
Comparisons
![≈ ( 0.14 ≈ 1/7 ) × relative molecular mass of fullerene ( ≈ 721 )](../image_source/8943ecee5e1763f42a8d1a8c42b7550a.png)
≈ ( 0.14 ≈ 1/7 ) × relative molecular mass of fullerene ( ≈ 721 )
![≈ 0.53 × relative molecular mass of caffeine ( ≈ 194 )](../image_source/8bd0e8855ed0c9f5b255989264f842af.png)
≈ 0.53 × relative molecular mass of caffeine ( ≈ 194 )
![≈ 1.7 × relative molecular mass of sodium chloride ( ≈ 58 )](../image_source/4c24be9232adc680e4abcccfeba87029.png)
≈ 1.7 × relative molecular mass of sodium chloride ( ≈ 58 )
Corresponding quantities
![Molar mass M from M = M_uM_r: | 102 g/mol (grams per mole)](../image_source/50223af667d0f20198e3c2aa511096eb.png)
Molar mass M from M = M_uM_r: | 102 g/mol (grams per mole)
![Molecular mass m from m = M_rM_u/N_A: | 1.7×10^-22 grams | 1.7×10^-25 kg (kilograms)](../image_source/789d56ec3d1af1916c169988b833f8a8.png)
Molecular mass m from m = M_rM_u/N_A: | 1.7×10^-22 grams | 1.7×10^-25 kg (kilograms)