NY Regents Chemistry Exam Jan 2023

Synthetic radioisotopes may be made by bombarding other nuclides with neutrons. The equations below represent a sequence of reactions converting stable iron–58 to cobalt–60, which is used in medical treatments.

82. State the neutron to proton ratio for an atom of the 58Fe in equation 1. [1] Mass is equal to the neutrons + protons.

Atom number is equal to the number of protons.

Fe has an atomic number of 26 (found on the Periodic Table)

58-26 = 32 neutrons

Answer: 32 neutrons to 26 protons

83. State, in terms of elements, why equation 2 represents a transmutation reaction. [1]

Transmutation reaction involves one element changing into another element. We can see in the equation 2, iron is changing to cobalt.

Answer: An atom of iron is changed to an atom of cobalt.

84.Identify the particle represented by *X *in equation 3. [1]
To figure out X, we must know that the sum of mass numbers must be equal on both sides of the equation and the sum of atomic numbers must be equal on both sides of the equation. Now, we can do some math.

59 +x = 60

x = 1 (mass number)

27+y = 27

y = 0 (atomic number)

Let's look at Table O on the Reference Table. Neutron has a mass of 1 and atomic number of 0.

Answer: neutron

85. Determine the fraction of an original sample of Co-60 that remains unchanged after 15.813 years. [1]

Table N on the Reference Table gives the half lives for all the radioisotopes. Cobalt-60 half life is 5.271 y.

15.813 years/5.271 = 3 half lives.

1 -> 1/2 -> 1/4 -> 1/8

Answer: 1/8