The half-life of calcium-47 about 5 days. Starting with 64 g of this isotope, what would be the amount remaining after 20 days?

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Answer 1 · 2016-08-03T01:19:12

The answer is 4 g.

Divide 64 by 2 four times, because there are four half-lives in 20 days.

Every half-life, the calcium-47 will lose half of the amount remaining.

$"20 days"/"5 days/half-life" = "4 half-lives"$ .

$"64 g"/2 = "32 g"$ after 1 half-life

$"32 g"/2 = "16 g"$ after 2 half-lives

$"16 g"/2 = "8 g"$ after 3 half-lives

$"8 g"/2 = "4 g"$ after 4 half-lives.