Rubidium-87 (Rb-87), which has a half-life of approximately 50 billion years, decays into strontium-87 (Sr-87). The following data table shows how the amount of Rb-87 in a certain rock changes over time. Approximately
what percentage of the original Rb-87 will remain in the rock when it is 2 billion years old? Round your
answer to the nearest thousandth of a percent.
After 0.02 half-
lives
After 0.04 half-
lives
After 0.06 half-
lives
After 0.08 half-
lives
95.926
94.606
98.623
97.265
percent of Rb-87
remaining

a. the law of proportion states the combination of 2 atoms in a specific ratio to produce multiple compounds such as the given statement of question ‘1st compound contains 88.8 % cu ’ indicates 88.8 g of cu is present along with 11.2 g oxygen in 100 g of compound whereas the statement ‘2st compound contains 79.9 % cu ’ indicates 79.9 g of cu is present along with 20.1 g oxygen in 100 g of compound

1st compound contains 88.8 g cu

for cu

m = 63 g /mol

atomic % = 88.8 /63 = 1.42

for o

m = 16 g /mol

atomic % = 11.2 /16 = 0.7

b. the emperical formula of 1st compound is

cu1.4o0.7

cu2o