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CHAPTER 19 REGULAR HOMEWORK:

NUCLEAR CHEMISTRY

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Question 1

What is the number of protons in Cl-35. (See PDF CH 19 SUPPLEMENT RH for meaning of Cl-35.)

Correct

 

Explanation

If the protons change the element changes so chlorine will always have 17 protons.. never more never less because then it would'nt be chlorine it would be one of its periodic table neighbors

 

Question 2

What is the number of neutrons?

Correct

 

Explanation

Take the mass number 35 an subtract the number of protons 17

35-17=18

 

Question 3

What is Z?

Correct

 

Explanation

  Z is the atomic/proton number

 

Question 4

What is A?

Correct

 

Explanation


  A is the mass number

 

Question 5

What is the number of protons in Cs-133? (See PDF CH 19 SUPPLEMENT RH for meaning of Cs-133.)

Correct

 

Explanation

Caesium will always have 55 protons 

 

Question 6

What is the number of neutrons?

Correct

 

Explanation

133-55=78

 

Question 7

What is Z?

Correct

 

    

    

 

Question 8

What is A?

Correct

 

    

    

 

Question 9

Using the periodic table, what is the element when Z = 33 and A = 75?
(Input symbol, remember neon is Ne NOT ne.)

 

Explanation

Z=proton number

So find the element on the periodic table with 33 as their atomic number aka Arsenic

 

Question 10

Using the periodic table, what is the element when the number of electrons is 28 and the charge on the ion is +3?

 

Explanation

28 + 3 = 31 (proton)

aka Gallium

 

Question 11

Calculate the neutron-to-proton ratio for O-17.

Correct

 

Explanation

8:9

 

Question 12

Does the above isotope lie within the band of nuclear stability? (Compare number of neutrons to number of protons with what is given in graph.)

Select one:
 Correct

 

    

    

 

Question 13

Calculate the neutron-to-proton ratio for Cu-68.

Correct

 

Explanation

29:39

 

Question 14

Does the above isotope lie within the band of nuclear stability?
Select one:
 Correct

 

    

    

 

Question 15

Calculate the neutron-to-proton ratio (to two decimal places) for Pu-239.

Correct

 

Explanation

94:145

1.542

 

Question 16

Identify the missing particles by balancing the mass and atomic numbers in each of the following nuclear decay equations.
See PDF CH 19 SUPPLEMENTS RH if reaction is missing.
Select one or more:
 Correct
 Correct

 

    

    

 

Question 17

Does Ga-67, the above isotope, lie within the band of nuclear stability?
Select one:
 Correct

 

    

    

 

Question 18

See PDF CH 19 SUPPLEMENTS RH if reaction is missing.
See PDF CH 19 SUPPLEMENTS RH if reaction is missing.

Select one or more:
 Correct
 Correct
 Correct

 

    

    

 

Question 19

See PDF CH 19 SUPPLEMENTS RH if reaction is missing.
See PDF CH 19 SUPPLEMENTS RH if reaction is missing.

Select one or more:
 Correct
 Correct
 Correct

 

    

   

 

Question 20

See PDF CH 19 SUPPLEMENTS RH if reaction is missing.
UPPLEMENTS RH if reaction is missing.

Select one or more:
 Correct
 Correct

 

    

    

 

Question 21

See PDF CH 19 SUPPLEMENTS RH if reaction is missing.
Select one or more:
 Correct
 Correct
 Correct

 

    

    

 

Question 22

Which of the following statements are true with respect to natural radioactive decay?

Select one or more:
 Correct
 Correct
 Correct
 Correct

 

    

    

 

Question 23

For each of the following radioactive nuclides, predict the mode of decay from its location in the periodic table and by comparing the mass number to the atomic mass of the element in the periodic table: 117Sb (For one type of decay more than one choice is correct.)

Select one or more:
 Correct
 Correct

 

    

    

 

Question 24

83Se

Select one or more:
 Correct

 

    

    

 

Question 25

42Ar

Select one or more:
 Correct

 

    

    

 

Question 26

How many α and β particles are emitted in the decay series that begins with Np-237 and finally produces the stable isotope Bi-209?

First, how many α (alpha) emissions?
Correct

 

    

    


 

Question 27

Second, how many β (beta) emissions?

Correct

 

    

    

 

Question 28

The radioactive decay of a certain sample produced 927 disintegrations per minute. Exactly 5.00 days later, the rate of decay was found to be 546 disintegrations per minute. Calculate the half-life, in days, for the decay of this sample.

Correct

 

Explanation

ln (Rt/Ro) = -kt

ln(546/927) = -k5

k=0.106

t1/2= 0.693/k = 6.56

 

Question 29

By mass spectral analysis, a sample of strontium is known to contain 2.64x1010 atoms of Sr-90 as the only radioactive element. The absolute disintegration rate of this sample is measured as 1238 disintegrations per minute. Calculate the half-life (in years) of Sr-90.

Correct

 

Explanation

R=KN

1238 = R(2.64e10)

k=4.689e-8

t1/2=0.693/4.7e8=14744680.9 min * 1 yr/525600 min = 28.12 yrs

 

Question 30

How long will it take (in years) for the disintegration rate of this sample to drop to 954 disintegrations per minute?

Correct

 

Explanation

ln(954/1238) = -4.7e-8(t)

t=5544442.166 min * 1hr/60 min * 1 day/24 hr *1 yr/ 365 day=10.5

 

Question 31

In a living organism, the decay of C-14 produces 15.3 disintegrations per minute per gram of carbon. The half-life of C-14 is 5730 years. A bone sample with 3.7 g of carbon has 25.7 disintegrations per minute. How old is the bone sample in years?

Correct

 

Explanation

t1/2 = 5730 yrs * 525600 min/year = 3011688000 min = 0.693/k

k=2.3e-10

ln(Rt/Ro)=-kt

25.7/3.7 = 6.954 dis/min*g

ln(6.945/15.3)=-(2.3e-10)t

3433455027*1 yr/525600 min=6532.33yrs

 

Question 32

What percentage of the atoms of carbon in the biosphere are C-14? Hint given in feedback.

Correct

 

Explanation

Hint, (want the number of C-14 atoms in 1 g)/(total C atoms in 1 g)x100%. Use rate = kN for number of C-14 and what you know about moles and Avogadro's number for the total number of C atoms in 1 g.


R=kN

15.3=2.3e-10(N)

N=6.65e10


1g * 1mol/12.011g * 6.022e23/1 mol = 5.01e22

%= 6.65e10/5.01e22 * 100 = 1.33e-10

 

Question 33

There are three isotopes of phosphorus. Only one of them is stable. Calculate the binding energy per nucleon (in MeV) for P-32 (atomic mass = 31.9739 u). mass H = 1.007825 u and mass n = 1.008665 u.

Correct

 

Explanation

# of protons = 15

15 * 1.007825 = 15.117

# of neutrons=15

15* 1.008665= 15.129975


mass defect = 30.24755-29.9783

=0.26905


0.26905 * 931.5 MeV/1 * 250.62 MeV


250.62MeV/30 = 8.354

 

Question 34

Which isotope of P is expected to be the most stable?

Select one:
 Correct

 

    

    

 

Question 35

When 239Pu is used in a nuclear reactor, one of the fission events that occurs is
See PDF CH 19 SUPPLEMENTS RH if reaction is missing.

The atomic mass of each atom is given below its symbol in the equation. Find the energy released (in kJ) when 5.10 g of plutonium undergoes this particular fission. Hint given in feedback.


 

Explanation

Hint, (1) Calculate the change in mass, expressed in atomic mass units, that accompanies this fission event. (2) Convert the mass loss to joules per fission. (3) Find the energy released per mole of plutonium. . .


Mass reactants-products

(1.008665+239.052)-(95.916+149.917+1.008665(4))

=240.060665-239.9

=0.193 * 1.66054e-27kg/1 = 3.2e-28 kg

E=mc^2

=(3.2e-28)(3e8)^2

=2.88e-11

2.88e-11J/atoms * 5.1 g Pu * 1mol/239 g * 6.022e23/1mol=3.7e11 J

=3.7e8 J

 

Question 36

One of the fission products that causes major concern is Sr-90, since it is incorporated into milk and other high-calcium foods. Sr-90 undergoes beta decay with a half-life of 28.1 years. What percentage of the Sr-90 that was formed in the detonation of the first fission bombs in August 1945 is still present in the environment in August 2044?

 

Explanation

t1/2= 0.693/k = 28.1 yr

k=0.024662

A= Ao(1/2)^n= 10(1/2)^3.523

n=(2044-1945)/28.1=3.523

A=.869

 

Question 37

One kilogram of high-grade coal produces about 2.8 x 104 kJ of energy when it is burned. Fission of one mole of U-235 releases 1.9 x 1010 kJ. Calculate the number of kg of coal needed to produce the same amount of energy as the fission of 1 kg of U-235 (235.05g/mol).

Correct

 

Explanation

1 kg U * 1000 g U / 11 g U * 1 mol/235.05 g * 1.9e10kg/1mol U * 1 kg coal/2.8e4 kJ=2.89e6 kg

 

Question 38

How many kilograms of sulfur dioxide (a major source of acid rain) are produced from the burning of the coal in question 1, if the coal is 0.76% by mass sulfur? Hint given in feedback.

Correct

 

Explanation

Remember to use the relation between the mass of S in coal and the mass of SO2.


2.89e6 kg * 0.76/100 * 100 kg SO2/50.1 kg S = 4.38e4

 

Question 39

Gaseous diffusion is used to enrich natural uranium in U-235. Use Graham’s law (see feedback) to calculate the ratio of enrichment of U-235 by a single diffusion of UF6. The atomic masses of the two principal isotopes of uranium are 235.0493 and 238.0508 for U-235 and U-238, respectively, and that of F is 18.9984. Use 4 decimal places.

Correct

 

Explanation

Remember that the rate of effusion is proportional to the average velocity which is inversely proportional to the square root of the mass. (vrms> = (3RT/M)0.5)

 

Question 40

What is the ratio of enrichment of U-235 after 37 diffusions of UF6?

 

Explanation

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