CHEM 001C Lecture Notes - Lecture 8: Acid Dissociation Constant, Sodium Hydroxide
CHEM 001C Lecture 8: Midterm 1 Review Chapters 13-15
●Dynamic Equilibrium
○Do strong acids or bases exhibit equilibrium?
■HCl → H+ + Cl-
■NaOH → Na+ + OH-
●No; they completely dissociate (no reactants left)
●Amphoteric
○Amphoteric: can act as an acid or base
●Ka
○What does Ka mean?
■Acid dissociation constant
■How likely an acid is to dissociate
○pKa < 1 → stronger acid → larger Ka
○Example: Calculate the pH of a solution of 1.00 M HCN and 5.00 M HNO2
■HCN + H2O ⇌ H3O+ + CN- Ka = 6.2 x 10-10
■HNO2 + H2O ⇌ H3O+ + NO2
-Ka = 4.0 x 10-4
■H2O + H2O ⇌ H3O+ + OH-Kw = 1.0 x 10-14
●HNO2 will dissociate the most: produce the most products
HNO2(aq)
H2O(l)
⇌
H+(aq)
NO2
-(aq)
5.00 M
-
0
0
-x
-
+x
+x
5.00-x
-
x
x
●Ka = 4.0 x 10-4 = ≅
x2
5.00 −x
x2
5.00
○x = 4.5 x 10-2 = [H+]
○pH = 1.35
■pH with HCN and HNO2 = 1.346
●K value is so small for the other two, the
effect on equilibrium concentration is so
small (not noticed)
Document Summary
Chem 001c lecture 8: midterm 1 review chapters 13-15. No ; they completely dissociate (no reactants left) Amphoteric : can act as an acid or base. How likely an acid is to dissociate. Pk a < 1 stronger acid larger k a. Example : calculate the ph of a solution of 1. 00 m hcn and 5. 00 m hno 2. Hcn + h 2 o h 3 o + + cn - k a = 6. 2 x 10 -10. Hno 2 + h 2 o h 3 o + + no 2 . H 2 o + h 2 o h 3 o + + oh - Hno 2 will dissociate the most: produce the most products. X = 4. 5 x 10 -2 = [h + ] Ph with hcn and hno 2 = 1. 346. K value is so small for the other two, the effect on equilibrium concentration is so small (not noticed)
