CHE 1302 Study Guide - Midterm Guide: Pyridinium, Buffer Solution, Formula Unit
21 Sep 2019
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Common ion effect and buffers: a solution is prepared that contains 25. 0 ml pyridine, c5h5n, d = 0. 978 g/ml and 27. 6 g pyridinium hydrochloride, c5h5nhcl. The volume of the aqueous solution is 250. 0 ml. What is the ph of this buffer solution? (kb c5h5n = 1. 5 . The concentrations are found using standard conversion techniques [c5h5n] = [25. 0 ml (0. 978 g / 1 ml) (1 mol / 79. 10 g)] / 0. 250 l = 1. 24 m. [c5h5n. hcl] = [27. 6 g (1 mol / 115. 56 g)] / 0. 250 l = 0. 955 m (as a side note, pyridinium hydrochloride is just a salt containing the conjugate acid of pyridine, c5h5nh+. Since each formula unit of the salt gives one pyridinium ion, the concentration of the conjugate acid can be taken as. The h-h equation is written in terms of ka, the equilibrium constant for the ionization of a weak acid. In this question we are given kb for the weak base.
