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Sergio [31]
3 years ago
14

If a substance has a half life of 58 years and starts with 500 g radioactive, how much remains radioactive after 30 years?

Chemistry
1 answer:
Vilka [71]3 years ago
5 0

Answer:

A = 349 g.

Explanation:

Hello there!

In this case, since the radioactive decay kinetic model is based on the first-order kinetics whose integrated rate law is:

A=Ao*exp(-kt)

We can firstly calculate the rate constant given the half-life as shown below:

k=\frac{ln(2)}{t_{1/2}} =\frac{ln(2)}{58year}=0.012year^{-1}

Therefore, we can next plug in the rate constant, elapsed time and initial mass of the radioactive to obtain:

A=500g*exp(-0.012year^{-1} *30year)\\\\A=349g

Regards!

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    n = (8.2 x 10²⁴ atoms N)(1 molecule dipyrithione/ 2 atoms of N)(1 mole dipyrithione/ 6.022 x 10²³ molecules dipyrithione)

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Answer:

The percent by mass of copper in the mixture was 32%

Explanation:

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According to the reaction, 4 mol HNO₃ will react with 1 mol Cu and produce 1 mol Cu²⁺. Since we have 0.237 mol HNO₃, the amount of Cu that could react would be (0.237 mol HNO₃ * 1 mol Cu / 4 mol HNO₃) 0.06 mol. This reaction would produce 0.060 mol Cu²⁺, however, only 0.010 mol Cu²⁺ were obtained, indicating that only 0.010 mol Cu were present in the mixture. This means that the acid was in excess, so we can assume that all copper present in the mixture has reacted.

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6 0
3 years ago
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