Carbonic acid, as well as bicarbonate and carbonate anions, are abundant in the
ID: 898797 • Letter: C
Question
Carbonic acid, as well as bicarbonate and carbonate anions, are abundant in the ocean, and pay a fundamental role in the ocean with respect to balancing carbon dioxide (CO_2) in the environment, and specifically acts to effectively "absorb" CO_2 from the atmosphere. As such, one of the consequences of increased CO_2 in the atmosphere is increased ocean acidification. Carbonic acid, H_2CO_3, is a diprotic acid that dissociates, losing its two protons, into bicarbonate, HCO_3^-, and carbonate, CO_3^2-, according to the following two step reaction. As a diprotic system, it has two dissociation constants, and specifically pH_a1 = 6.3 and pK_a2 = 10.3, for these two steps. You titrate a 50.0 mL solution 0.50 M H_2CO_3 with a 1.00 M solution of the strong base, NaOH. What are the two expected equivalence volumes for your titration?Explanation / Answer
50 ml , 0.5 M H2CO3 with 1 .0 M NaOH
1)
at first equivalence volume of NaOH = 12.5 ml
at second equivalence volume of NaOH = 25 ml
explanation :
at equivace point 1 :
moles of acid = moles of base
25 x 0.5 = 1.0 x V
V = 12.5 ml
at equivalence point 2 :
moles of acid = 2 x moles of base
50 x 0.5 = V x 1.0
V = 25 ml
2 )
H2CO3 + OH- ----------------> HCO3 - + H2O
50 x 0.5 30 x 1 0 0
25 30 0 0
0 5 25 0
strong base OH- remained in the solution . so pH can be decided by strong base
[OH-] = millimoles / total volume
= 5 / (50 + 30)
= 5/ 80
= 0.0625
pOH = -log[0.0625]
pOH = 1.2
pH +pOH = 14
pH = 12.8