A Typical PH Problem
Calculate the pH and percentage protonation of a .20 M aqueous solution of pyridine, C5H5N. The Kb for C5H5N is 1.8 x 10−9.
First, write the proton transfer equilibrium:
The equilibrium table, with all concentrations in moles per liter, is
| C5H5N | C5H6N+ | OH- | |
|---|---|---|---|
| initial normality | .20 | 0 | 0 |
| change in normality | -x | +x | +x |
| equilibrium normality | .20 -x | x | x |
| Substitute the equilibrium molarities into the basicity constant | |
| We can assume that x is so small that it will be meaningless by the time we use significant figures. | |
| Solve for x. | |
| Check the assumption that x << .20 | ; so the approximation is valid |
| Find pOH from pOH = -log with =x | |
| From pH = pKw - pOH, | |
| From the equation for percentage protonated with = x and initial = .20, |
This means .0095% of the pyridine is in the protonated form of C5H5NH+.
Read more about this topic: Weak Base
Famous quotes containing the words typical and/or problem:
“Sinclair Lewis is the perfect example of the false sense of time of the newspaper world.... [ellipsis in source] He was always dominated by an artificial time when he wrote Main Street.... He did not create actual human beings at any time. That is what makes it newspaper. Sinclair Lewis is the typical newspaperman and everything he says is newspaper. The difference between a thinker and a newspaperman is that a thinker enters right into things, a newspaperman is superficial.”
—Gertrude Stein (1874–1946)
“... your problem is your role models were models.”
—Jane Wagner (b. 1935)