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? 
Science
If the initial amount of Carbon14 in the mammoth was 8 grams, how many halflives have passed i the fossil sample has 1 gram left? 
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 …