If 350 mg of a radioactive element decays to 250 mg in 36 hours, what is its half-life?
2007-08-08 18:35:21 · 3 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
100mg in 36 hrs - 50mg in 36 hrs - 25 mg in 36 hrs - 12.5 mg in 36 hrs - 6.75mg in 36 hrs... lets see, that brings it down to 155.75mg in 180 hrs...you take it from here. If you have a calc with an n! button, try n!36, gl
p.s. the guy above is nuts. How can it take 36 hrs for 100mg and 25 for 250?
2007-08-08 18:51:57 · answer #1 · answered by thrag 4 · 0⤊ 0⤋
250mg/36 hrs = 6.9444444mg/hr. Half of 350mg is 175 mg so you need to find out how long it takes to decay 175mg(/6.94mg/hr----divide to cancel out mg)=25hours.
2007-08-08 18:47:04 · answer #2 · answered by thatfatguypat 2 · 0⤊ 0⤋
you have the formula
A(t) =A0* 2^(-t/T) where T is the half-life, A(t) activity at time t, A0, activity at time 0
We suppose activity is proportionnal to weight
So A(36) = A0 * 2^(-36/T)
A(36)/A0 = 2^(-36/T)
A0/A36= 2^(36/T)
A0/A36 = 350/250=1.4= 2^(36/T)
(36/T) = log (base2)1.4=0.485
T=36/0.485=123.6 hours = 123 hours, 36 minutes
2007-08-08 19:04:40 · answer #3 · answered by maussy 7 · 0⤊ 0⤋