After 62.0 hours , 1.0 g remains unchanged from a sample of 42K . How much 42K was in the original sample?

Respuesta :

The half-life of K-42 is 12.360 hours.


62 hours is just about 5 half-lives, so we'd expect about 1/32 of the original amount to remain after that time. (32 = 2^5)


In fact, it's 12.36 / 62 = 5.016 half-lives.


2^5.016 = 32.36

So if you started with 32.36g in the original sample, it would have decayed down to 1g after 5.016 half-lives.

"32 g" 42K was in the original sample.

According to the question,

  • Time, t = 62.0 hours
  • Remaining, N = 1 g
  • K half life = 12.36 hrs

As we know,

→ [tex]n = \frac{t}{K_{1/2}}[/tex]

      [tex]= \frac{62}{12.36}[/tex]

      [tex]= 5.016[/tex]

hence,

The original sample will be:

→ [tex]N = N_o(\frac{1}{2} )^n[/tex]

or,

→ [tex]N_o = N\times 2^n[/tex]

By substituting the values, we get

        [tex]= 1\times (2)^{5.016}[/tex]

        [tex]= 32 \ g[/tex]

Thus the above approach is right.

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