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ale4655 [162]
3 years ago
14

If the half-life of a radioisotope is 20,000 years, then a sample in which three-quarters of that radioisotope has decayed is __

_________ years old
Chemistry
1 answer:
poizon [28]3 years ago
4 0
25% remaining = 40,000 years old
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2Pb(s) + O2(aq) + 4H+(aq) → 2H2O(l) + 2Pb2+(aq)
defon

Answer:

The answer to your question is 0.269 g of Pb

Explanation:

Data

Lead solution = 0.000013 M

Volume = 100 L

mass = 0.269 g

atomic mass Pb = 207.2 g

Chemical reaction

                        2Pb(s) + O₂(aq) + 4H⁺(aq) → 2H₂O(l) + 2Pb₂⁺(aq)

Process

1.- Calculate the mass of Pb in solution

Formula

Molarity = \frac{number of moles}{volume}

Solve for number of moles

Number of moles = Volume x Molarity

Substitution

Number of moles = 100 x 0.000013

Number of moles = 0.0013

2.- Calculate the mass of Pb formed.

                       207.2 g of Pb ----------------- 1 mol

                             x g             ----------------- 0.0013 moles

                        x = (0.0013 x 207.2) / 1

                        x = 0.269 g of Pb                                                                

8 0
3 years ago
Read 2 more answers
A sample of 10.6 g of KNO3 was dissolved in 251.0 g of water at 25 oC in a calorimeter. The final temperature of the solution wa
finlep [7]

Answer:

36.55kJ/mol

Explanation:

The heat of solution is the change in heat when the KNO3 dissolves in water:

KNO3(aq) → K+(aq) + NO3-(aq)

As the temperature decreases, the reaction is endothermic and the molar heat of solution is positive.

To solve the molar heat we need to find the moles of KNO3 dissolved and the change in heat as follows:

<em>Moles KNO3 -Molar mass: 101.1032g/mol-</em>

10.6g * (1mol/101.1032g) = 0.1048 moles KNO3

<em>Change in heat:</em>

q = m*S*ΔT

<em>Where q is heat in J,</em>

<em>m is the mass of the solution: 10.6g + 251.0g = 261.6g</em>

S is specififc heat of solution: 4.184J/g°C -Assuming is the same than pure water-

And ΔT is change in temperature: 25°C - 21.5°C = 3.5°C

q = 261.6g*4.184J/g°C*3.5°C

q = 3830.87J

<em>Molar heat of solution:</em>

3830.87J/0.1048 moles KNO3 =

36554J/mol =

<h3>36.55kJ/mol</h3>

<em />

6 0
3 years ago
What process do plants undergo to produce chemical energy?
Ahat [919]

Answer:

i think photosynthesis

6 0
3 years ago
A 22.4 kg object is accelerating at 1.40 m/s2. What net force is being applied to the object?
kaheart [24]

Answer:

<h3>The answer is 31.36 N</h3>

Explanation:

The force acting on an object given it's mass and acceleration can be found by using the formula

force = mass × acceleration

From the question we have

force = 22.4 × 1.4

We have the final answer as

<h3>31.36 N</h3>

Hope this helps you

3 0
3 years ago
The electron-domain geometry of a carbon-centered compound ch4 is tetrahedral. the hybridization of the central carbon atom is _
Nata [24]
The  hybridization  of  the   central  carbon  compound  CH4  tetrahedral  is
SP^3 hybridization 

In   tetrahedral  molecular  geometry    a central atom  is  located  at the  center  with  4  substituent  that  are located at  the  corners  of  tetrahedron. Example  in methane  molecules  is made  up of  b equally  spaced sp^3  hybrid  orbital  forming  bond  angle  of   109.5
5 0
3 years ago
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