# The half life of thallium-201 is 21.5 hours. We have 85 g of thallium-201 how many grams will be left after 10 half-lives?

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• 2 months ago

A = A₀ (1/2)^(t/h)

A = 85g (1/2)^10

A = 0.0830078125g

3 sigfigs: 8.30 x 10^-2 g

• Dr W
Lv 7
2 months agoReport

how many sig figs does 85 have?  why 3 sig figs in your final answer?

• Anonymous
2 months ago

I don't know, I hope I helped you Ok?

Good afternoon and stay with God 🙏😉

• Dr W
Lv 7
2 months ago

that's an AMAZING sample of Thallium you have there Kalayvonna.  Because

.. (1) the half life of Tl-201= 72.9 hr (according to literature)

.. (2) Tl-201 is not naturally occurring.  it's produced in cyclotrons at point

.. . .. .of use (or nearby point of use) at a rate of about 1 picogram / μ AH

So how you would have an 85.g sample of Tl-201 with a half life = 21.5hrs is beyond me!  Oh wait.. this is another one of those make believe questions that some instructors throw together without much thought.  I get it now!

***********

<sigh>.. use this equation

.. At = Ao * (1/2)^(t / half life)

.. At = 85.g * (1/2)^10

.. At = 0.083g

• 2 months ago

85 x (1/2)^10 =>

85 X 0.000976...

0.08388 g

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• Zirp
Lv 7
2 months ago

2¹⁰=1024, so a little less than 1/1000

• 2 months ago

(85 g) x (1/2)^10 = 0.083 g