GS CBT 9 PS section #16

[yjj8817]

---

Members do not see this ad.

16) H2SO4 has Ka1 = 1.0 x 103 and Ka2 = 1.2 x 10-2. What is the approximate hydrogen ion concentration of 1.0 M H2SO4?

1. 1.00 M
2. 1.01 M
3. 1.05 M
4. 1.10 M

INCORRECT:

Your Answer: n/a
Correct Answer: B


Can someone explain how they got 0.01M for H+ concentration from Ka2?

 

[chemtopper]

16) H2SO4 has Ka1 = 1.0 x 103 and Ka2 = 1.2 x 10-2. What is the approximate hydrogen ion concentration of 1.0 M H2SO4?

1. 1.00 M
2. 1.01 M
3. 1.05 M
4. 1.10 M

INCORRECT:

Your Answer: n/a
Correct Answer: B


Can someone explain how they got 0.01M for H+ concentration from Ka2?

Hi
H2SO4 is a strong acid and is clearly indicated by its first acid dissociation which is very high,We will take that removal of first is 100%.So [H+] is 1M and you need not to make any ICE table for it.
I have made it just to show you why is it 1.0M
H2SO4(aq) ------> H+ (aq) + HSO4-(aq)
Initial 1.0 0 0
change -1.0 +1.0 +1.0
final 0 1.0 11.0

now second dissociation constant is very low so ICE table will help in calculating the final concentration
HSO4- (aq) <----> H+ (aq) + SO42-(aq)
Initial 1.0 (from above) 1.0 (from above ) 0.0
change -x 1.0+x +x
final 1.0-x 1.0+x x
now approximation rule for simplification
1.0-x = 1.0
1.0+x = 1.0
Ka2 = [H+][HSO4-]/ [H2SO4 ]
= x (1.0)/ 1.0
x= 1,2X10^-2
x= 0.012M
so total H+ concentration = 1.0 + x (from ICE table)= 1.012 M = 1.01M (B)