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m_a_m_a [10]
2 years ago
7

A rock has 12.5 percent of its original amount of potassium-40 remaining in it; potassium-40 has a half-life of 1.25 billion yea

rs. How long ago was the rock formed?
a) 1.25 billion years ago

b) 2.5 billion years ago

c) 3.75 billion years ago

d) 5 billion years ago
Chemistry
2 answers:
igor_vitrenko [27]2 years ago
7 0
A rock has 12.5 percent of its original amount of potassium-40 remaining in it; potassium-40 has a half-life of 1.25 billion years. <span>3.75 billion years ago</span> was the <span>rock formed. the answer is letter C</span>
mylen [45]2 years ago
6 0

Answer:

the answer is b) 2.5 billion years.  if its half life is 1.25 billion years and there is only 25% of the element remaining, you would take 1.25 billion and multiply it by two to get 2.5 billion.

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In an aqueous solution of a certain acid the acid is 0.10% dissociated and the pH is 4.06. Calculate the acid dissociation const
Kruka [31]

Answer : The acid dissociation constant Ka of the acid is, 8.7\times 10^{-5}

Explanation :

First we have to calculate the concentration of hydrogen ion.

pH=-\log [H^+]

Given: pH = 4.06

4.06=-\log [H^+]

[H^+]=8.71\times 10^{-5}M

The dissociation of acid reaction is:

                         HA\rightarrow H^++A^-

Initial conc.      c        0         0

At eqm.           c-cα    cα       cα

Given:

Degree of dissociation = α = 0.10 % = 0.001

[H^+]=c\alpha

8.71\times 10^{-5}=c\times 0.001

c=0.0871M

The expression of dissociation constant of acid is:

K_a=\frac{[H^+][A^-]}{[HA]}

K_a=\frac{(c\times \alpha)\times (c\times \alpha)}{(c-c\alpha)}

Now put all the given values in this expression, we get:

K_a=\frac{(0.0871\times 0.001)\times (0.0871\times 0.001)}{(0.0871-0.0871\times 0.001)}

K_a=8.7\times 10^{-5}

Thus, the acid dissociation constant Ka of the acid is, 8.7\times 10^{-5}

7 0
3 years ago
Rocks are classified as igneous, sedimentary, or metamorphic based primarily on
irinina [24]

Answer:

Method of formation

Explanation:

7 0
2 years ago
How many moles of solid naf would have to be added to 1.0 l of 2.39 m hf?
sp2606 [1]
Molarity is one way of expressing concentration and is equal to the number of moles of the solute per liter of the solution. Therefore,

Molarity = 2.39 mol / L solution

2.39 ( 1.0) = 2.39 mol HF

Hope this answers the question.
6 0
3 years ago
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RoseWind [281]

structural, plant and animal cells are very similar because they are both eukaryotic cells. they both contain membrane-bound organelle such as the nucleus, endoplasmic, mitochondria etc

8 0
2 years ago
What are the correct coefficients when this equation is balanced?
larisa86 [58]

4, 3, 1

Explanation:

Sb has four on the right, so it needs four on the left. It's all alone, so <u>4</u>.

O2 comes in pairs, so you only need <u>3</u> of those to get six oxygens.

And 1 is the place holder for the right side since we got the left to match perfectly.

6 0
3 years ago
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