In the two cited molecules br is more electronegative

In the two cited molecules, Br is more electronegative
than I. Therefore, the O-H bond in HBrO
3
is weaker than the O-H bond in HIO
3
, so HBrO
3
is the stronger
acid.
b. HNO
2
, HNO
3
HNO
3
> HNO
2
.
Four electronegative groups in HNO
3
, vs three in HNO
2
, result in a more polar O-
H bond, and therefore a weaker O-H bond.
K
a
HNO
3
large
HNO
2
7.2 x 10
-4
c. HOCl, HOI
HOCl > HOI
. Cl is more electronegative than I. This results in a more polar O-H bond, and
therefore a weaker O-H bond.
d. H
3
PO
4
, H
3
PO
3
H
3
PO
4
> H
3
PO
3
.
H
3
PO
4
has 5 electronegative groups separating the O-H as compared to the 4
electronegative groups in H
3
PO
3.
This makes the O-H bond in H
3
PO
4
more polar and therefore weaker.
Chem 162-2015 Chapter 17 Tro Acid-Base Equilibria 19

STRENGTHS OF CARBOXYLIC ACIDS
CH
3
CH
2
COOH
Propanoic acid
K
a
= 1.3 x 10
-5
I-CH
2
CH
2
COOH Cl-CH
2
CH
2
COOH CH
3
CHClCOOH CH
3
CCl
2
COOH
3-Iodopropanoic acid 3-Chloropropanoic acid 2-Chloropropanoic acid 2,2-Dichloropropanoic acid
K
a
= 8.3 x 10
-5
K
a
= 1.0 x 10
-4
K
a
= 1.4 x 10
-3
K
a
= 8.7 x 10
-3
Chem 162-2015 Chapter 17 Tro Acid-Base Equilibria 20

STRENGTHS OF AMINES AS BASES
Recall that a Bronsted-Lowry base is anything that tends to react with a proton.