Asked by kate


a 275mL sample of vapor in equilibrium with 1-propylamine at 25C is removed and dissolved in 0.500L of H20. For 1-propalamine, Kb=3.72*10^-4 and the vapor pressure at 25C is 215 torr.
(a)What should be the pH of the aqueous solution?
(b) How many mg of NaOH dissolved in 0.500L of water give the same pH
Answered by DrBob222
First you need to determine the molarity of the propylamine solution (the 0.5L soln). I would use PV = nRT and solve for n (P = 0.275). Then n in 0.5 L will give you the M of the propylamine.
PrNH2 + HOH ==> PrNH3^+ + OH^-
Kb = (PrNH3^+)(OH^-)/(PrNH2)
Set up an ICE chart, substitute into the above Kb expression, solve for OH^-, then convert to pH.
(b)should be easy enough after you have (a).
Answered by kate
Can you give the steps for working this?
Answered by DrBob222
The steps are above. Just follow the directions.
Answered by kate
will the pH be 11.20
Answered by kate-------------------------------------
can you please check my answer? and how do i possibly find the molarity of the NaOH?
Answered by DrBob222
I worked it through once, without checking it, and obtained pH 10.88. I solved this equation.
Kb = (X^2)/(0.00234-x). I solved the quadratic and used 316 torr and not 215. I get 11 if I don't solve the quadratic.
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