Question

Question #13933

Answer 1

`4.0 * 10^(-5)"mM"`

Explanation:

Extracellular fluid, or ECF, is being kept at a pH of approximately `7.4`, which means that the concentration of hydrogen ions, `"H"^(+)`, is

`["H"^(+)] = 10^(-"pH")`

`["H"^(+)] = 10^(-7.4) = color(green)(4.0 * 10^(-8)"M")`

In the context of extracellular liquid, it's useful to express this value in milimoles per liter, or milimolar

`4.0 * 10^(-8)color(red)(cancel(color(black)("moles")))/"L" * (10^3"mmoles")/(1color(red)(cancel(color(black)("mole")))) = 4.0 * 10^(-5)"mM"`

By comparison, the concentration of sodium cations, `"Na"^(+)`, is in the range

`["Na"^(+)] = "136-145 mEq/L"`

and the concentration of bicarbonate anions, `"HCO"_3^(-)`, is in the range

`["HCO"_3^(-)] = "22-28 mM"`

For example, the concentration of the bicarbonate anions is

`(28color(red)(cancel(color(black)("mM"))))/(4.0 * 10^(-5)color(red)(cancel(color(black)("mM")))) = 7 * 10^5`

higher than the concentration of hydrogen ions.

As a cool fact, concentrations of hydrogen ions that either exceed `12.0 * 10^(-5)"mM"` or fall below `2.0 * 10^(-5)"mM"` are not compatible with life.