Rubidium is a soft, silvery-white metal that has two common isotopes: rubidium-85 and rubidium-87. The actual mass of rubidium-85 is 84.91179 amu. The atomic mass of rubidium is 85.47 amu. If the abundance of rubidium-85 is 72.17% and the abundance of rubidium-87 is 27.83%, what is the actual mass of rubidium-87

86.91757 amu

Explanation:

From the question given above, the following data were obtained:

Isotope A (rubidium-85)

Mass of A = 84.91179 amu

Abundance of A = 72.17%

Atomic mass of rubidium = 85.47 amu

Isotope B (rubidium-87):

Abundance of B = 27.83%

Mass of B =?

The actual mass of rubidium-87 can be obtained as follow:

Atomic mass = [(Mass of A × A%)/100] + [(Mass of B × B%)/100]

85.47 = [(84.91179 × 72.17)/100] + [(Mass of B × 27.83)/100]

85.47 = 61.28084 + (Mass of B × 0.2783)

Collect like terms

85.47 – 61.28084 = Mass of B × 0.2783

24.18916 = Mass of B × 0.2783

Divide both side by 0.2783

Mass of B = 24.18916 / 0.2783

Mass of B = 86.91757 amu

Thus, the mass of rubidium-87 is 86.91757 amu

the only liquid elements at standard temperature and pressure are bromine (br) and mercury (hg). although, elements caesium (cs), rubidium (rb), francium (fr) and gallium (ga) become liquid at or just above room temperature.

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