<h3>Half-life of a radioactive element </h3>
The Half-Life of a radioactive element osbtime taken for half the nucleus of the atom of the element to decay
<h3>Calculating the original amount of U-238</h3>
- The number of moles present in each element is first determined:
- Number of moles = mass/molar mass
<h3>For Pb-206:</h3>
mass = 0.37 mg = 0.37 * 10⁻³ g
molar mass = 206 g/mol
number of moles = 0.37 * 10⁻³ g/206 g/mol
number of moles of Pb-206 = 1.79 * 10⁻⁶ moles
<h3>For U-238:</h3>
mass = 0.95 mg = 0.95 * 10⁻³ g
molar mass = 238 g/mol
number of moles = 0.95 * 10⁻³ g/238 g/mol
number of moles = 3.99 * 10⁻⁶ moles
Assuming that all the Pb-206 were formed from U-238
- Initial moles of U-238 = Moles of present U-238 + molesw of present Pb-208
Initial moles of U-238 = 3.99 * 10⁻⁶ moles + 1.79 * 10⁻⁶ moles
Initial moles of U-238 = 5.78 * 10⁻⁶ moles
One mole of U-238 contains = 6.02 * 10²³ atoms
5.78 * 10⁻⁶ moles of U-238 will contain 6.02 * 10²³ * 5.78 * 10⁻⁶ atoms
Number of atoms of U-238 initially present = 3.48 * 10¹⁸ atoms
Therefore, the number of atoms of U-238 initially present is 3.48 * 10¹⁸ atoms
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