Answer :
Answer:
15.0 g
Explanation:
We are given;
- Original sample of Thallium-208 as 120.0 g
- The number of half lives as 3
We are required to calculate the remaining mass after three half lives
- We are going to use the formula;
N = N₀ × 0.5^n
where, N is the remaining mass, N₀ is the original mass and n is the number of half lives.
Therefore;
N = 120.0 g × 0.5^3
= 15.0 g
Thus, the remaining mass of Thallium-208 is 15.0 g
Alternatively;
- Since after every half life the mass reduces by half of the original then we can half a chain showing the reduction after three half lives;
120.0 g → 60.0 g (120 × 0.5) → 30.0 g (60 × 0.5) → 15.0 g (30 × 0.5)
- Therefore, the remaining mass after three half lives is 15.0 g