In: Chemistry
If the value of the equilibrium constant, K, for the reaction below is less than 1, what is the strongest base in this system?
HCN (aq) + HCO3¯ (aq) CN¯ (aq) + H2CO3 (aq)
Which of these acids is the strongest in aqueous solution?
a) H3PO4
b) H2SO3
c) HClO3 answer
d) HOCl
In this reaction H2CO3 and HCN act as base. Among these two HCN is weak acid.
It can be explained by looking the structure of both H2CO3 and HCN
H2CO3
In H2CO3 , central atom carbon is bonded with wo hydroxy group it can yield two protons in solution.
In HCN ,carbon is the central atom and it forms triple bond with nitrogen and a single bond with hydrogen.
HCN is a weak acid since carbon is hesitant to donate hydrogen atom, because C-H keeps the molecule stable.A strong acid donates protons when water is added.Therefore HCN is a weak acid.
CN- is conjugate base of HCN and HCO3- is conjugate base of H2CO3.
Because HCN is a weak acid its conjugate base is strong.i
2)Acidity can also be explained in terms of oxidation number of the central atom. i.e Higher the oxidatation number higher the acidity. Here central atom of H3PO4 and HClO3 has high oxidation state .Among these HClO3 is more acidic. Because in H3PO4 , number of O-H group attached is two , as the number of O-H bond attached to central atoms increase stability of its conjugate base decreases due to the participation of lone pair of electrons on oxygen in cross conjugation.
CROSS CONJUGATION leads to extra resonanating structures, where delocalisation of negative charge on conjugate base will be less effective.