Question

A noble gas consists of three isotopes of masses of 19.99 amu, 20.99 amu, and 21.99 amu. the relative abundances of these isotopes are 90.92%, 0.257%, and 8.82% respectively. what is the average atomic mass of this noble gas? what noble gas is this?

Answer 1

Neon

Step-by-step explanation:

Average Atomic Mass is calculated using following formula,

= [ (Mass of Isotope 1 × % Natural Abundance) + (Mass of Isotope 2 × % Natural Abundance) + ...... (Mass of Isotope n × % Natural Abundance) ] ÷ 100

Data Given:

Mass of Isotope 1 = 19.99 amu

% Natural Abundance of Isotope 1 = 90.92

Mass of Isotope 2 = 20.99 amu

% Natural Abundance of Isotope 2 = 0.257

Mass of Isotope 3 = 21.99 amu

% Natural Abundance of Isotope 3 = 8.82

Solution:

Putting values in formula,

Average Atomic Mass = [ (19.99 × 90.92) + (20.99 × 0.257) + (21.99 × 8.82) ] ÷ 100

Average Atomic Mass = (1817.49 + 5.394 + 193.95) ÷ 100

Average Atomic Mass = 20.16

Result:

Consulting Periodic Table it was found that the noble gas with Average Atomic Mass of 20.16 ≈ 20.18 is Neon.