Question

1. Evaluate how much "weight" (mass, strictly speaking) an average human loses daily due to gas exchange while breathing. Find all necessary data, indicate your sources, and present a detailed calculation. 2. 10.00 g of a Mg-Al alloy completely dissolved in hydrochloric acid. The volume of hydrogen gas given off in the chemical reaction is 12.29 L. Find the mass composition (in mass %) of the alloy. Assume that the volume of 1 mole of gas is 22.4 L.

Answer 1

Multiple questions (not specifically mentioned question to be answered ), as per guideline only first will be answered.

1. Average Human Body mass = 70 kg

Average no. of breathe = 15 / minute

(Ref. The Merck Manuel for Medical Information: Home Edition)

During gas exchange weight loss is due to exhaling CO₂ , so body weight loss is due to loss of Carbon as  CO₂.

Each breath exchanges 500 ml of air.

(Ref =Kapit, W., et al., 1987: The Physiology Coloring Book. HarperCollins.)

CO₂ is 4-5% of exhaled volume by volume. (of Inhaled it is 0.04 % )

(Ref. : www.newton.dep.anl.gov )

Volume of CO₂ exhaled per breathe = 0.044 * 500 ml = 22 ml .

Amount of  CO₂ exhaled during a day = 22 ml * 15* 60*24 = 475.2 L

If we assume CO₂ behaves as ideal gas ; ( Volume of 1 mol = 24.4 L at 25 C )

No. of moles of CO₂ =  475.2 L / 24.4 L = 19.48 moles

1 carbon molecule = 1 molecule of CO₂ .

No. of Moles of Carbon lost = 19.48 moles .

Weight of Carbon loss = 19.48 moles * 12 g/ mol = 233.7 g

So, a average human loses ~234 g of body mass daily due gas exchange while breathing.