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mario62 [17]
3 years ago
8

What mass of a 60.0-gram sample of N-16 will remain unchanged after 28.8 seconds?

Chemistry
1 answer:
Yanka [14]3 years ago
7 0
The answer is 3.75 g.

Half-life is the time required for the amount of a sample to half its value.
To calculate the fraction of the sample remained unchanged, we will use the following formulas:
1. (1/2)^{n} = x,
where:
<span>n - a number of half-lives
</span>x - a remained fraction of a sample

2. t_{1/2} = \frac{t}{n}
where:
<span>t_{1/2} - half-life
</span>t - <span>total time elapsed
</span><span>n - a number of half-lives
</span>
The half-life of N-16 is 7.13.
So, we know:
t = 28.8 s
<span>t_{1/2} = 7.13 s

We need:
n = ?
x = ?
</span>
We could first use the second equation, to calculate n:
<span>If:
t_{1/2} = \frac{t}{n},
</span>Then: 
n = \frac{t}{ t_{1/2} }
⇒ n = \frac{28.8 s}{7.13 s}
⇒ n=4.04
<span>⇒ n ≈ 4
</span>
Now we can use the first equation to calculate the remained amount of the sample.
<span>(1/2)^{n} = x
</span>⇒ x=(1/2)^4
<span>⇒x= \frac{1}{16}


If the fraction of the sample is 1/16 = 6.25%, then the mass of the sample could be calculated as:
x g : 6.25% = 60 g : 100% 
x = </span>
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