
Concept explainers
Interpretation: It is given that, radon is present as 1.0 g per 7.0 metric ton of a pitch ball. The number of radon atoms that can be isolated from given mass of pitch-blende is to be calculated. The number of radon atoms remain in 2025 is to be calculated if 15 mg radon is manufactured in 1925.
Concept introduction: Amount of radon left is calculated using the formula,
AE=A00.5t/t1/2
To determine: The number of radon atoms that can be isolated from 1.75×108 g pitch-blende; the number of radon atoms remain in 2025, if 15 mg radon is manufactured in 1925.

Answer to Problem 116IP
Answer
Number of radon (Ra) atoms that can be isolated from 1.75×108 g pitch-blende is 6.66×1022 atoms_. Number of radon (Ra) atoms left in 2025 is 3.82×1019 Ra atoms_.
Explanation of Solution
Mass of radon (Ra) is 25 g_.
Given
Mass of pitch-blende is 1.75×108 g.
The conversion of gram (g) into kilogram (kg) is done as,
1 g=10−3 kg
Hence,
The conversion of 1.75×108 g into kilogram is,
1.75×108 g=(1.75×108×10−3) kg=1.75×105 kg
Since, radon is present as 1.0 g per 7.0 metric ton of a pitch ball, mass of radon is calculated as,
Mass of Ra=Mass of pitch-blende×1.0 g Ra7.0 metric ton×(1 metric ton1000 kg)
Substitute the value of mass of pitch-blende in the above equation.
Mass of Ra=Mass of pitch-blende×1.0 g Ra7.0 metric ton×(1 metric ton1000 kg)=1.75×105 kg×1.0 g Ra7.0 metric ton×(1 metric ton1000 kg)=25 g_
Number of radon (Ra) atoms that can be isolated from 1.75×108 g pitch-blende is 6.66×1022 atoms_.
Mass of radon is 25 g.
Formula
The number of radon atoms is calculated as,
Atoms of Ra= Mass of Ra×1 mol RaAtomic mass of Ra×6.022×1023 atoms 1 mol Ra
Substitute the values of mass and atomic mass of radon in the above equation.
Atoms of Ra= Mass of Ra×1 mol RaAtomic mass of Ra×6.022×1023 atoms 1 mol Ra=25 g×1 mol Ra226.0 g×6.022×1023 atoms 1 mol Ra=6.66×1022 atoms_
Number of radon (Ra) atoms in 15 mg is 3.99×1019 atoms_.
Given
Mass of radon atoms is 15 mg.
Half life of radon is 1.60×103 years.
Atomic mass of radon is 226 g.
The conversion of milligram (mg) into gram (g) is done as,
1 mg=10−3 g
Hence,
The conversion of 15 mg into gram is,
15 mg=(15×10−3) g=15×10−3 g
Formula
The number of radon atoms is calculated as,
Atoms of Ra= Mass of Ra×1 mol RaAtomic mass of Ra×6.022×1023 atoms 1 mol Ra
Substitute the values of mass and atomic mass of radon in the above equation.
Atoms of Ra= Mass of Ra×1 mol RaAtomic mass of Ra×6.022×1023 atoms 1 mol Ra=15×10−3 g×1 mol Ra226.0 g×6.022×1023 atoms 1 mol Ra=3.99×1019 atoms_
Number of radon (Ra) atoms left in 2025 is 3.82×1019 Ra atoms_.
Half life of radon is 1.60×103 years.
Number of radon (Ra) atoms in 15 mg is 3.99×1019 atoms.
Total time from 1925 to 2025 is,
2025−1925=100 years
Formula
Amount of radon left is calculated using the formula,
AE=A00.5t/t1/2
Where,
- AE is the amount of radon left.
- A0 is the original amount of radon.
- t1/2 is the half-life.
- t is the total time.
Substitute the values of t1/2,t and A0 in the above equation.
AE=A00.5t/t1/2=3.99×1019 Ra atoms×(0.5)100 years1600 years=3.82×1019 Ra atoms_
Conclusion
The calculated value of number of radon (Ra) atoms left in 2025 is 3.82×1019 Ra atoms_. Number of radon (Ra) atoms in 25 g is 6.66×1022 atoms_
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