586
h1ARTIN
[CONTRIBUlIOS P R O N
KILPATRICK AND K. DEAN EANES
Vol. 7 5
CHEMISTRY O F THE USIVERSITY O F PENSSYLVANIA CHEMISTRY O F ILLINOIS INSTITUTE O F TECHSOLOGY 1
TIXE 1 ) E P A R l Y E N 'I O F
A N D THE
DEPARTMEXI'
OF
The Dissociation Constants of Acids in Salt Solutions. 11. Acetic Acid R u MARTIN KILPXTRICK .ZKD K.DEANEANES RECEIVED Aucusr 4, 1'352 The dissociation constant of acetic acid is deterinitled irith benzoic itcid atid the solvated protoil salt soktions of the alkali halides.
The dissociation constant of acetic acid in salt solutions was determined by two sets of measurements, the first being against the reference acid the solvated proton, as described in paper one of the series,' and the second by measurement of the cell.
1
1I
HAC 0.005M HB 0.005 JI Au MAC 0.005 MI MC1 hfB 0 005 .\I I Au lO0.V~ MCl S ilf , MC1 'Y ;M Quinhytirone Quinhydroiic
1,
1
which after suitable small corrections for the change in buffer ratios gives directly the equilibrium constant for the reaction HAC
where
+R
€IB -{ A c -
(11
(2)
and K A , Bis~the ratio of the dissociation constant OS acetic acid t o that of benzoic acid. Column I1 of Table I gives the values of this ratio for aqueous solutions of potassium, sodium and lithium chloride. Column I11 gives the dissociation constant of acetic acid calculated from the dissociation constant of benzoic acid in the corresponding salt solutions. Column IV gives the results of the measurements against hydrochloric acid while columns V and VI give the results of Harned and Murphy2 and Harned and Hickey3.' from measurements of cells without liquid junction TAHLL
I
I)ISSOCIATII)S C O ' \ \ I A h l OF ~ 4 C h l I iA L I I 3 4 1 I%lectrolyte, moledllter Reference lii,nO A r x lo'-- acid -P Benzoic Benioic Hydrochloric
Z-)"
-
Potassium chloride 0.285 2.59" 2.65' 2.57" ,280 2 . 8 2 2.81 2.79 ,277 2.89 3.03 2.99 276 2 . 9 9 ,273 :3 . [J.> ,269 3 . 0 6 .267 3,114 ,263 2.9:: .2B1 2.89 ,267 2.8;i
.3.12
3.07
. 17
3; . (61
3.20 :{.I2 .?l4
3 .ox 3.07
2.99
3.01 2.95
2.8.5
28X
. 263
27.5 2 3 0
2.81
,246
2 4.;
2.3i
,237 2.10 1.7.7 ,219 1 4 : ; ,227
2.41 1.99 1.62 1.31
1.91 1.50 1 7;
Kc A ,
2.5Td 1 . y 2.84 1.61 3 . 10 1 .63 3.21 1 .70 3 .27 1 .T4 3.25 :3.21 :
