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URGENT

Fluorine-20 has a half-life of 11 seconds. Identify the amount of fluorine-20 left from a 25 gram sample after 55 seconds.


A 0.78125 g
B 78125 mg
C 0.6352 g
D 7.8124 g

2 Answers

2 votes

Answer

0.78125 g

Explanation:

Divide the time period by the half life.The value of t is 5.

A = P(0.5)t Write the formula.

A = 25(0.5)^5 Substitute 25 for P and 5 for t.

= 0.78125 g

User Rbenvenuto
by
8.3k points
4 votes

Answer:

A. 0.78 g

Explanation:

The half-life of F-20 (11 s) is the time it takes for half of it to decay.

After one half-life, half (50 %) of the original amount will remain.

After a second half-life, half of that amount (25 %) will remain, and so on.

We can construct a table as follows:

No. of Fraction Mass

half-lives t/s Remaining Remaining/g

0 0 1 25

1 11 ½ 12.5

2 22 ¼ 6.2

3 33 ⅛ 3.1

4 44 ¹/₁₆ 1.6

5 55 ¹/₃₂ 0.78

6 66 ¹/₆₄ 0.39

We see that 0.78 g of F-20 remain after five half-lives (55 s).

User Mad Dog Tannen
by
8.3k points
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