Input interpretation
![rubidium fluoride | relative molecular mass](../image_source/f5470f6e01b7a22b0f054aa4fc15599b.png)
rubidium fluoride | relative molecular mass
Result
![Find the relative molecular mass, M_r, for rubidium fluoride: 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: RbF Use the chemical formula to count the number of atoms, N_i, for each element: | N_i F (fluorine) | 1 Rb (rubidium) | 1 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 F (fluorine) | 1 | 18.998403163 Rb (rubidium) | 1 | 85.4678 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 F (fluorine) | 1 | 18.998403163 | 1 × 18.998403163 = 18.998403163 Rb (rubidium) | 1 | 85.4678 | 1 × 85.4678 = 85.4678 M_r = 18.998403163 + 85.4678 = 104.4662](../image_source/c5a8c81e4687261d49d2c610a3a7e2a9.png)
Find the relative molecular mass, M_r, for rubidium fluoride: 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: RbF Use the chemical formula to count the number of atoms, N_i, for each element: | N_i F (fluorine) | 1 Rb (rubidium) | 1 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 F (fluorine) | 1 | 18.998403163 Rb (rubidium) | 1 | 85.4678 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 F (fluorine) | 1 | 18.998403163 | 1 × 18.998403163 = 18.998403163 Rb (rubidium) | 1 | 85.4678 | 1 × 85.4678 = 85.4678 M_r = 18.998403163 + 85.4678 = 104.4662
Comparisons
![≈ ( 0.14 ≈ 1/7 ) × relative molecular mass of fullerene ( ≈ 721 )](../image_source/fd6f837ff64eaa2c62ded48e0fb9e442.png)
≈ ( 0.14 ≈ 1/7 ) × relative molecular mass of fullerene ( ≈ 721 )
![≈ 0.54 × relative molecular mass of caffeine ( ≈ 194 )](../image_source/387282a57b26caea9cdf1817a1553100.png)
≈ 0.54 × relative molecular mass of caffeine ( ≈ 194 )
![≈ 1.8 × relative molecular mass of sodium chloride ( ≈ 58 )](../image_source/2beed493ee041454c231d6a2906a315c.png)
≈ 1.8 × relative molecular mass of sodium chloride ( ≈ 58 )
Corresponding quantities
![Molar mass M from M = M_uM_r: | 104 g/mol (grams per mole)](../image_source/8f33dbb711047eafcf4deddd92c87d14.png)
Molar mass M from M = M_uM_r: | 104 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/499295e466ddf8426115ab250b012ee8.png)
Molecular mass m from m = M_rM_u/N_A: | 1.7×10^-22 grams | 1.7×10^-25 kg (kilograms)