The Solubility of Oxygen in an Aqueous Salt Solution, Blood, and Seawater
a. Compare the solubility of oxygen in water containing 0.15 MNaCl to the solubility in pure water.
b. Compare the solubility of oxygen in seawater and in pure water. Seawater can be approximated as containing 35 grams of NaCl per kg of water.
a. From Eq. 11.1-19 and data in the table, we have
\log \frac{S_{ i }\left(M_{ s }\right)}{S_{ i }\left(M_{ s }=0\right)}=\log \frac{S_{ i }\left(M_{ s }\right)}{S_{ i , o }}=-K_{ s , i } \cdot M_{ s } (11.1.19)
\log \frac{S_{ O _{2}}}{S_{ O _{2}, o }}=-K_{ NaCl , O _{2}} \cdot M_{ NaCl }=-0.14 \times 0.15=-0.021
so that
\frac{S_{ O _{2}}}{S_{ O _{2}, o }}=10^{-0.021}=0.951
Therefore, the solubility of oxygen in an aqueous solution of 0.15 M NaCl is about 95 percent that in pure water. Since a 0.15MNaCl solution has some of the same properties as blood (as we show elsewhere in this book, it has the same osmotic pressure and freezing point), we can expect that the solubility of oxygen in blood is also about 5 percent less than in pure water.
b. Since the molecularweight of NaCl is 58.44, themolality of seawater is 35/58.44 = 0.60 M. Thus,
\frac{S_{ O _{2}}}{S_{ O _{2}, \circ}}=10^{-0.14 \times 0.6}=0.824
Therefore, seawater contains appreciably less dissolved oxygen than pure water or blood.