Complete these half-life problems. Show all work How much of a 100.0 g sample of

Question

Complete these half-life problems. Show all work How much of a 100.0 g sample of198 Au is left after 8.10 days if its half-life is 2.70 days? A 50.0 g sample of16 N decays to 12.5 g in 14.4 seconds. What is the half life? The half-life of42 K is 12.4 hours. How much of a 750 g sample is left after 62.0 hours? What is the half-life of99 Tc, if a 500 g sample decays to 62.5 g in 639,000 years? The half-life of232 Th is 1.4-10^10 years. If there are 25.0 g of the sample left after 2.8 times 10^10 years, how many grams were in the original sample? There are 5.0 g of131 I left after 40.35 days. How many grams were in the original sample if its half life is 8.07 days?

Explanation / Answer

3 )

a ) t = 8.1 days

      t1/2   = 2.7 days

     a = initial = 100g

    t = n t1/2

   8.1 = n x 2.7

n = 3

remaining = a / 2^n = 100 / 2^3 = 12.5 g

(b)

a = 50 g

remaining = 12.5

remaining = a / 2^n

12.5 = 50 / 2^n

n= 2

t = n t1/2

14.4 = 2 x t1/2

t1/2 = 7.2 sec

(c)

t = n t1/2

62 = n x 12.4

n = 5

remaing = a /2^n = 750 / 2^5 = 23.44g

(d)

reaming = a /2^n

62.5 = 500 / 2^n

n= 3

t = n t1/2

639000 = 3 x t1/2

t1/2 = 213000years

note : remaing two same formula same procedure . try to solve they are very easy. thank you

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