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igomit [66]
3 years ago
11

Potassium-40 has a half-life of 1.3 billion years. as the potassium-40 isotope decays, it becomes argon. if a rock was formed wi

th 12 g of potassium-40, approximately how long would it take for 75% of the potassium-40 to be replaced by argon?
a. 1.3 billion years
b. 2.6 billion years
c. 5.2 billion years
d. 650 million years
Chemistry
2 answers:
Marina CMI [18]3 years ago
3 0
The half life of a substance is the time taken by a radioactive substance to decay by half its original mass. In this case, the half life of Potassium-40 is 1.3 billion years. 
Original mass of Potassium-40 = 12 g (100%)
New mass after the decay = 3 g ( 25 %, since 75% was replaced by argon)
New mass = Original mass × (1/2)^n ; where n is the number of half lives. 
 3 = 12 × (1/2)^n
(1/2)^n = 1/4 
      n = 2 
Therefore; the time taken will be 1.3 × 2 = 2.6 Billion years
Rom4ik [11]3 years ago
3 0

Answer:Potassium is a crucial element for the healthy operation of the human body. Potassium occurs naturally in our environment (and thus our bodies) as three isotopes: Potassium-39, Potassium-40, and Potassium-41. Their current abundances are 93.26%, 0.012% and 6.728%. A typical human body contains about 3.0 grams of Potassium per kilogram of body mass.

How much Potassium-40 is present in a person with a mass of 80 kg?

If, on average, the decay of Potassium-40 results in 1.10 MeV of energy absorbed, determine the effective dose (in Sieverts) per year due to Potassium-40 in an 80-kg body. Assume an RBE of 1.2. The half-life of Potassium-40 is 1.28 x 109 years.

Explanation:

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Answer: 3.024 g grams of hydrogen are needed to  convert 76 grams of chromium(III) oxide, Cr_{2}O_{3}

Explanation:

The reaction equation for given reaction is as follows.

Cr_{2}O_{3} + 3H_{2} \rightarrow 2Cr + 3H_{2}O

Here, 1 mole of Cr_{2}O_{3} reacts with 3 moles of H_{2}.

As mass of chromium (III) oxide is given as 76 g and molar mass of chromium (III) oxide (Cr_{2}O_{3}) is 152 g/mol.

Number of moles is the mass of substance divided by its molar mass. So, moles of Cr_{2}O_{3} is calculated as follows.

No. of moles = \frac{mass}{molar mass}\\= \frac{76 g}{152 g/mol}\\= 0.5 mol

Now, moles of H_{2}.given by 0.5 mol of Cr_{2}O_{3} is calculated as follows.

0.5 mol Cr_{2}O_{3} \times \frac{3 mol H_{2}}{1 mol Cr_{2}O_{3}}\\= 1.5 mol H_{2}

As molar mass of H_{2} is 2.016 g/mol. Therefore, mass of H_{2} is calculated as follows.

No. of moles = \frac{mass}{molar mass}\\1.5 mol = \frac{mass}{2.016 g/mol}\\mass = 3.024 g

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7 0
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The kinetic energy and the physical state of water depend strongly on the temperature;

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As the temperature increases, the speed of colliding molecules increases and the kinetic energy increases.

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The correct answer is option c, that is, nucleus.  

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