Question

assuming that all of the following substances are permeable across a selectively permeable membrane, which of the following molecules would you predict to move fastest across the membrane?
multiple choice
iodine (mw = 127 g/mol)
glucose (mw = 180 g/mol)
hydrochloric acid (mw = 36 g/mol)
sucrose (mw = 342 g/mol)
citric acid (mw = 192 g/mol)

Explanation:

Smaller - sized molecules generally diffuse faster across a selectively - permeable membrane. Among the given substances, the molecular weight is an indicator of size (lower molecular weight implies smaller size in this context). Hydrochloric acid has the lowest molecular weight among them, so it is expected to move fastest.

Answer:

C. hydrochloric acid (mw = 36 g/mol)