Deuterium 2H 20140 u is sometimes used to replace the princi

Deuterium, 2H (2.0140 u), is sometimes used to replace the principal hydrogen isotope 1H in chemical studies. The percent isotopic abundance of deuterium is 0.015%. If it can be done with 100% efficiency, what mass of hydrogen gas would have to be processed to obtain a sample containing 2.80×1021 2H atoms? Express the mass of hydrogen gas in grams to three significant figures.

Solution

Since we need 2.80x10^21 deuterium atoms.

convert the number of atoms into moles.
(2.80x10^21)/(6.02x10^23)=4.65x10^-3 moles

So, number of moles of natural hydrogen we need

= (4.65x10^-3)/(0.015%)=31.0 mol

Therefore, mass of hydrogen = moles * molar mass of H

Mass of hydrogen = 31 mol * 1.01 gmol-1

Mass of hydrogen = 31.3 g