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# The atomic mass and natural abundance of the naturally occuring isotopes of hydrogen are shown in th

NY Chemistry Regents Exam June 2019

Questions 52-54

The atomic mass and natural abundance of the naturally occuring isotopes of hydrogen are shown in the table below. The isotope H-2, also called deuterium, is usually represented by the symbol “D.” Heavy water forms when deuterium reacts with oxygen, producing molecules of D2O.

52 Explain, in terms of subatomic particles, why atoms of H-1, H-2, and H-3 are each electrically neutral.

Solution: Each atom has protons (positively charged) and electrons (negatively charged). When the number of protons is equal to the number of electrons, the atom is electrically neutral.

Answer: Equal number of protons and neutrons

53 Determine the formula mass of heavy water, D2O.

Solution: The formula mass is determined by multiplying the mass of each atom (from the Periodic Table) by the number of atoms. Deuterium is H-2 according to the passage, which means it has a mass of 2.

D = 2*2 = 4

O = 16*1 = 16

4+16 = 20 g/mol

54 Based on Table N, identify the decay mode of tritium.

Solution:Tritium is H-3 according to the chart. 