How to Calculate Half-Life for First Order Reactions

[@deisydutan9832]

when I multiplied 0.42*3= 1.26 where did you get 2.31

[@Favour7153]

Pls can you solve the this problem : the half life of an element strotinuim 90 is 28.8yrs .if the element was accidental released how long does it take for Its concentration to fall to 1percent of the original concentration

[@medsciencestreamlined126]

Hey Paris, thanks for your comment. On first reading your question I noticed the wording was a little strange- while it is a real element if you meant to type "strontium-90" (molar mass of 89.9 g/mol), it mentions "concentration" as a metric which is most often referred to with solutions/dilutions rather than half-life problems. The problem doesn't imply that the strontium is in a solution of water or anything though. However, my assumption is that whoever posed this question meant to ask "how long does it take for the mass of a strontium-90 sample to be reduced to 1% of its original mass", because assuming that the strontium-90 is not in a solution and is just in released into the air or environment, its molar mass should be the same regardless of the amount of the sample has decayed meaning the "concentration" of grams per mole has not changed. As I mentioned, "concentration" is a weird metric to use here, but perhaps they are referring to molar mass which is grams per mole which should not be dictated by the number of grams of sample you have left. Your problem does not mention a starting "concentration" or sample mass for that matter, but in this case we can just start by plugging in our knowns- half life = 0.693 / k 28.8 years = 0.693 / k now you can solve for k and use k to find out how long it would take for a sample of 1 gram or 100 gram or whatever you choose to plug in to be reduced to 1% of its initial mass (which all should be relatively straightforward to calculate). Again, the question itself seems flawed in my opinion and I feel like you couldn't be faulted for misunderstanding it but the general purpose with any question teachers pose to students is to gauge the students' understanding, so my approach would be to answer the question I think they are trying to ask me and also offer an explanation as to your approach based on the definition of the terms (such as concentration) and your corresponding approach to solving the problem to the best of your ability. Sorry my response is so lengthy, I hope this helps and best of luck with your studies Paris! I really appreciate your comment!

[@Favour7153]

@@medsciencestreamlined126 Thanks for the reply. Noted.