Regents Chemistry Exam August 2022

Tritium, hydrogen-3, is a radioisotope.

63. State the number of neutrons in an atom of tritium. [1]

The number of neutrons is equal to the mass number - number of protons (atomic number). Tritium is hydrogen-3 as stated by the given. Number 3 represents the mass. Let's take a look at the Periodic Table on the Reference Table. Hydrogen has an atomic number of 1. To find the number of neutrons, we subtract 1 from 3.

**Answer:** 2

64. Complete the nuclear equation *in your answer booklet *for the decay of tritium by writing a notation for the missing nuclide. [1]

To complete a nuclear equation, we must make sure that the sum of atomic masses (numbers on the top right) are equal on both sides and the sum of atomic number (numbers on bottom right) are equal on both sides of the arrow. We see 3 on the left and 0 on the right, the missing atomic mass must be 3. For atomic numbers we see 1 on the left of the arrow and -1 to the right. 1=-1+x , x =2. The missing atomic number must be 2. Now, all we have to do is find the correct element with atomic number 2 on the periodic table. The element is He.

The missing element is

65. Based on Table *N*, identify a nuclide that has the same decay mode as tritium, but has a longer half-life. [1]

Let's take a look at Table N on the Reference Table:

It gives nuclides and their half lives. Tritium is hydrogen-3 as stated in the given. According to the Table N, it has a half life of 12.31 years and decay mode of **β**-. Let's take a look at all the nuclides with the same decay mode. They are: Au-198 C-14, Co-60, Cs-137, I-131, K-42, Kr-85, N-16, P-32, Sr-90, Tc-99. Who has a half life longer than 12.31 years? C-14, Cs-137, Sr-90, Tc-99

Please note that in the chart d is for days, y is for years, s is for seconds, H is for hours.

**Answer:** Any of the following: C-14, Cs-137, Sr-90, Tc-99