Question

Table 18.2 (continued) 18.20 Solutions Tested pH [H(M) [C,H,O, (M) Percent Dissociation | 0.10 M HCH 0, 2.14 0.010 M HCH 0, 13.09 0.0010 M HC,H,O 284 Question Write the net ionic equation describing the dissociation of acetic acid in aqueous solution. Question Calculate (H) and C.H.O.- for each concentration above, showing a sample cal- culation here Question Write the equilibrium constant expression for acetic acid, and calculate a Kvalue and an apparent percent dissociation for each concentration, showing sample calculations here. Question What is the effect of dilution on the percent dissociation? Why should this behavior be expected Instructor's Initials: Tonic Equilibria, pH, Indicators, and Buffers 57

Answer 1

1) Net ionic equation is

CH3COOH(aq) + H2O(1) + CH3C00-(aq) + H30+(aq)

2) pH = - log[H+]

[H+] = 10-2.79 = 0.0016 M

[CH3COO-] = [H+]

3)

LH002*HD / 60*H||_002*HD =

= 0.0016 * 0.0016 / 0.10

= 2.56 * 10-5

Percent dissociation =(amount of dissociated acid / total amount of acid)*100

=(0.0016 / 0.10)*100

= 1.6 %

Degree of dissociation increses with dilution because dissociation of acid happens with the help of energy generated when water molecule dissociates so more water molecule means more energy and hence better dissociation of acid.