The reaction can go to completion by removing OH$$-$$ ions by adding
A
CO2
B
SO2
C
HCl
D
KOH
Explanation
KOH is the base thus, it gives OH–
ions thus
it cannot remove OH–
ions from reaction mixture
but it adds on the concentration of OH–
ions.
So,
an acid must be added but if a strong acid is added
to the reaction mixture then in acidic condition the
MnO4–
formed reduces to give Mn2+ thus, HCl
which is a strong acid and SO2 which on treating
with water forms a strong H2SO4 cannot be used
for this purpose.
Thus, CO2 which forms H2CO3 a
weak acid reacts to remove OH–
but not that much
acidic that MnO4–
undergo reduction. Thus, CO2 is
used for this reaction for completion.
2
AIPMT 2012 Prelims
MCQ (Single Correct Answer)
Buffer solutions have constant acidity and alkalinity because
A
these give unionised acid or base on reaction with added acid or alkali
B
acids and alkalies in these solutions are shielded from attack by other ions
C
they have large excess of H+ or OH$$-$$ ions
D
they have fixed value of pH
Explanation
For this example,
CH3COOH ⇌ CH3COO– + H+ ;
CH3COONa ⇌ CH3COO– + Na+
when few drops of HCl are added to this buffer,
the H+ of HCl immediatly combine with
CH3COO– ions to form undissociated acetic
acid molecules. Thus there will be no H+ ions to
combine with CH3COO– ions to form
undissociated acetic acid molecules. Thus there
will be no appreciable change in its pH value.
Like wise if few drops of NaOH are added, the
OH– ions will combine with H+ ions to form
unionised water molecule. Thus pH of solution
will remain constant.
3
AIPMT 2012 Mains
MCQ (Single Correct Answer)
Given that the equilibrium constant for the reaction,
2SO2(g) + O2(g) $$\rightleftharpoons$$ 2SO3(g) has a value of 278 at a particular temperature. What is the value of the equilibrium constant for the following reaction at the same temperature ?
SO3(g) $$\rightleftharpoons$$ SO2(g) + $${1 \over 2}$$ O2(g)
Given the reaction between 2 gases represented by A2 and B2 to give the compound AB(g),
A2(g) + B2(g) $$\rightleftharpoons$$ 2AB(g)
At equilibrium, the concentration of
A2 = 3.0 $$ \times $$ 10$$-$$3 M, of B2 = 4.2 $$ \times $$ 10$$-$$3 M, of AB = 2.8 $$ \times $$ 10$$-$$3 M
If the reaction takes place in a sealed vessel at 527oC, then the value of Kc will be