Chemistry
posted by John
How many halflives have passed if 87.5% of a substance has decomposed? How many if 99.999% has decomposed?
For 87.5% decomposition 1/8 is left.
(1/8) = (1/2)^3
Three half lives is the answer
Fot 99.999% decomposition, 10^5 is left.
Solve 10^5 = (1/2)^n for the number of halflives, n. Take the log of each side of the equatiuon for a quick solution.
Respond to this Question
Similar Questions

halflife
1. The halflife of a firstorder reaction is 9.89 minutes. How many minutes will have elapsed after 27 halflives? 
MATH 156
Write the numbers in order of increasing size. "can anyone please help me I think the answer is A am I correct? 
Science Half Lives
I am confused about how to claculate half lives. Can you explain. ( How much of a 400 gm sample od gold is left after 10.8 days if the half life is 2.7) 
science
how many halflives have passed if 87.5% of a substance has decomposed? 
Chemistry
K42 has a halflife of 12.4 hours. If you begin with 250g of K42, determine how much you will have left after 4 halflives. How long does 4 halflives take? 
science
Using absolute dating,a fossil is dated to be 3 million years old and decomposed 1 halflife. If it takes the same fossil 12 million years to decompose to 4 halflives,how old will the fossil be when it is measured to be at 3halflives? 
chemistry
Find the number of disintegrations per minute emitted by 1.1 mol of 232Th in 1 min. The halflife of 232Th is 1.4 x 1010 year I was able to do this with the following technique: 1.1 x 6.022 x10^23 =6.62x10^23 1.4x10^10=7.358x10^15 … 
chemistry
what fraction of an original sample of a radioactive isotope remains after three halflives have passed? 
Chemistry
A substance undergoes a firstorder decomposition. After 40.0 min at 500 degrees C, only 12.5% of the original sample remains. What is the halflife of the decomposition? 
math
The half life of the radio active substance is the time require the half the substance to decay. the mount A ( in grams) of 100 gram sample of a radio active substance remaining after t half lives by A equals to 100 (0.5) t. suppose …