Answer to Question #190648 in General Chemistry for Kevin

Question

How many half-life cycles does it take for a sample of radioactive isotope to reach 12.5% of its original mass?

Answer 1

If we start with 100% of a sample , we can keep dividing this number by 2 until we reach 12.5% to find out how many half lives passed.

Remember, when the sample is still 100%, 0 half lives have passed.

% remaining: 100 > 50 > 25 > 12.5

Half lives: -------0------1------2-------3

3 half lives passed.