The half life for the radioactive decay of rubidium-87 to strontium-87 is ×4.881010 years.Suppose nuclear chemical analysis shows that there is 0.337mmol of strontium-87 for every 1.000mmol of rubidium-87 in a certain sample of rock. Calculate the age of the rock.Round your answer to 2 significant digits.
Question
The half life for the radioactive decay of rubidium-87 to strontium-87 is ×4.881010 years.Suppose nuclear chemical analysis shows that there is 0.337mmol of strontium-87 for every 1.000mmol of rubidium-87 in a certain sample of rock. Calculate the age of the rock.Round your answer to 2 significant digits.
Solution
To solve this problem, we need to use the formula for radioactive decay, which is:
N = N0 * (1/2)^(t/T)
where: N is the final quantity of the substance, N0 is the initial quantity of the substance, t is the time that has passed, and T is the half-life of the substance.
In this case, we know that the ratio of Sr-87 to Rb-87 is 0.337/1.000. This means that 1 - 0.337 = 0.663 of the Rb-87 has decayed into Sr-87.
So, we can set up the equation as follows:
0.663 = 1 * (1/2)^(t/4.88*10^10)
To solve for t, we can take the natural log of both sides and use the properties of logarithms to simplify:
ln(0.663) = (t/4.88*10^10) * ln(1/2)
Solving for t gives:
t = (ln(0.663) / ln(1/2)) * 4.88*10^10
Calculating this gives:
t ≈ 3.6 * 10^10 years
So, the rock is approximately 36 billion years old. However, rounding to 2 significant digits gives us an age of 3.6 billion years.
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