Question & Answer: 90 Sr Half life = 28.1 years What is the initial mass of 90 Sr if after 200 years, 1.00 grams…..

90 Sr Half life = 28.1 years

What is the initial mass of 90 Sr if after 200 years, 1.00 grams is left undecayed?

Expert Answer

For a first order reaction rate constant , k = ( 2.303 /t )x log ( Mo / M)

Where

Mo = initial mass = ?

M= Mass left after time t = 1.00 g

K = rate constant = 0.693 /t1/2 = 0.693 / 28.1 = 0.025 year^-1

t = time = 200 years

Plug the values we get  log ( Mo / M) = (kt) / 2.303

= 2.142

Mo / M = 102.142 = 138.6

Mo = 138.6×1.00 = 138.6 g

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