What percent of hydrochloric acid is hydrogen?
A clearer way to think about this question is to ask: What percent of hydrogen chloride is hydrogen? (Hydrochloric acid results when hydrogen chloride is added to an aqueous solution.)
Hydrogen chloride contains one hydrogen atom and one chlorine atom per molecule. The mass of these two atoms are 1.01 amu for hydrogen and 35.45 amu for chlorine. Thus every individual molecule of hydrogen chloride contains a total mass of 1.01 + 35.45 = 36.46 amu
To find the mass percent of hydrogen in hydrogen chloride, we must divide the weight of the hydrogen atom alone by the weight of the entire molecule.
1.01 / 36.46 = 0.0277
Then we multiply by 100% to find the percentage.
0.0277 x 100% = 2.77%
Thus, 2.77% of the mass of hydrogen chloride is hydrogen.