Question

Many cold water fish species do not survive in warmer water. Some scientists hypothesize that the amount of dissolved oxygen in the water (which fish breathe) is responsible. The model describing the amount of oxygen dissolved in water is Henry’s Law. Henry’s Law constants are temperature dependent; a model for how Henry’s Law constants (for oxygen dissolved in water) change with temperature is:

K_H(T)=(0.0013 Mol/kJ*bar) x (e^{1700 K(1/T -1/298/15K)})

(from https://webbook.nist.gov/cgi/cbook.cgi?ID=C7782447&Mask=10#Solubility). To test this hypothesis, we can calculate the concentration of dissolved oxygen in water at an Arctic temperature (0°C) and a tropical temperature (20°C).

A. Calculate the Henry’s Law constant values at 0°C and 20°C.

B. Calculate the molal concentrations of dissolved oxygen in water at these two

temperatures.

• Assume the total pressure is 1.00 bar, and 20.95% of the air is oxygen.

C. Is oxygen more soluble in water at higher or lower water temperatures? Explain.

D. What is the percentage change of the dissolved oxygen content as the temperature

changes?

E. Do your results support the hypothesis that the amount of dissolved oxygen at different

temperatures could explain why cold water fish species do not survive in warm water? Explain.

Answer 1

C) the oxygen is more soluble in water at lower temperature. The molality calculated for dissolved oxygen is more at lower temp than at higher temp.

D) M at 0^oC is 4.59*10^-4 mol/kg

M at 20^oC is 3.00*10^-4 mol/kg

therefore % change = (3.00*10^-4/4.59*10^-4)*100

= 65.36%

E) Yes. As cold water fishes require more amount of dissolved oxygen for their survival. When the water becomes warm the amount of dissolved oxygen decreses, hence they cannot get the amount of oxygen they require for their survival.