Consider a solution of CO _ 2 ( ~g ) dissolved in water in a closed container. Which one of the following plots correctly represents variation of log (partial pressure of CO _ 2 in vapour phase above water) [y-axis] with (mole fraction of CO _ 2 in water) [x-axis ] at 25^ C ?
B.
According to Henry's Law, the partial pressure of a gas in the vapour phase (p) is proportional to the mole fraction of the gas in the solution (x). The mathematical expression is: p = K_H x where K_H is the Henry's law constant. Taking logarithm on both sides: (p) = (K_H x) (p) = (K_H) + (x) Comparing this with the equation of a straight line y = mx + c: y = (p) (y-axis) x = (x) (x-axis) m = 1 (slope) c = (K_H) (y-intercept) Since K_H for CO_2 in water is a positive constant at 25^ C, (K_H) will be a constant intercept. The plot of (p) vs (x) is a straight line with a positive slope and a positive y-intercept. This corresponds to graph (2).
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