Chapter 18, Problem 1SEPP

Physical and Biological Sciences

In chemistry, the standard state for a solution is 1M. This means that each solute concentration expressed in molarity is divided by 1M. In biological systems, however, we define the standard state for the ${\text{H}}^{\text{+}}$ ions to be $1\times {10}^{-7}M$. Consequently, the change in the standard Gibbs free energy according to these two conventions will be different for reactions involving the uptake or release of ${\text{H}}^{\text{+}}$ ions, depending on which convention is used. We trill therefore replace $\Delta G\text{º with }\Delta G\text{º,}$ where the prime denotes that it is the standard Gibbs free-energy change for a biological process.

What is most likely the reason for the standard state for ${\text{H}}^{\text{+}}$ being defined as $1\times {10}^{-7}$ M in biological systems?

a)

It is an arbitrary convention.

b)

Physiological conditions reduce all concentrations by a factor of ${10}^7$.

c)

Physiological conditions increase all concentrations by a factor of ${10}^7$.

d)

Biological systems have a pH of about 7.