Please help me with these Chemistry questions.

Question

Radioactive Decay Graph

1. Answer these three questions about the graph.

Approximately what percentage of the isotope remains after 80 days?

What is the half-life of the isotope shown on the graph?

How long would it take a 20 g sample of Thorium-234 to decay into only 5 grams of Thorium-234?

2.How long would it take a 20 g sample of Thorium-234 to decay into only 5 grams of Thorium-234?

Answer 1

From the graph, approximately 10% remains after 80 days.

From the graph, the half life looks to be approximately 25 days. (The t_1/2 can be calculated to be 24.2 days.)

For 20 g to decay into 5 grams, it would take ~50 days (actually 48.4 days).

..... 5 g/20g = 0.25 which is 2 half lives must elapse. 2 half lives x 25 days/half live = 50 days.