Engineering Chemistry S Datta

202 ENGINEERING CHEMISTRY
Q. 24. What is the pH of a buffer solution containing 0.4 mol dm –3 methanoic
acid and 1.0 mol dm –3 sodium methanoate? pK a
(HCOOH) = 3.8.
Ans. pH = pK a
+ log 100 .
040 .
= 3.8 + 0.4 = 4.2.
Q. 25. Will
F NI HG
10 K J F
Mn +2 N I
containing
HG
100 K J H + be precipitated by passing H 2
S?
Ans. H 2
S 2H + + S –2 ; K =
2 −2
(0.01) × [S ]
∴ 1.1 × 10 –22 = =
[H S]
2
+ −2
[H ] [S ]
[H2S]
−2
(0.01) [S ]
0.1
= 1.1 × 10 –22
∴ [S –2 ] = 10 –19 . ∴ [Mn +2 ] [S –2 ] = 0.1 × 10 –19 = 10 –20
K sp
. (MnS) = 1.4 × 10 –15
So, ppt. will not be obtained.
[ Q S = 0.1M]
HS 2
EXERCISES
1. Deduce Ostwald’s dilution law and state its limitations.
2. Deduce the relation between solubility and solubility product of CaF 2
at room temperature.
3. Explain the terms: (i) Buffer solution (ii) Buffer capacity and (iii) Buffer action.
4. Explain the following–Aqueous solution of NaCl conducts electricity while chlorine water does
not conduct electricity.
5. Which are the strongest Lewis acids in the series? (a) BF 3
, BCl 3
, BI 3
; (b) BeCl 2
, BCl 3
.
6. Tricovalent phosphorus compounds can serve as Lewis bases and also as Lewis acids–comment.
7. The reaction HCl (aq) + KOH (aq) → KCl (aq) + H 2
O is neutralisation according to:
(a) Bronsted-Lowry concept, (b) Lewis theory and (c) Solvent system concept. Elucidate.
8. Deduce the Hendersen equation and state its utility.
9. What do you mean by common-ion effect? How is it utilized in qualitative chemical analysis?
10. What do you mean by autoprotolysis of water?
11. Derive an expression for ionic product of water. Show that it is different from dissociation constant
of water.
12. Give the Bronsted-Lowry concept of acids and bases.
13. What is the basic equation for acid-base reaction of Bronsted theory?
14. Explain (a) neutralisation, (b) hydrolysis, in the light of Bronsted theory.
15. What is a buffer solution? Explain buffer action.
16. Derive an expression for pH of the buffer solutions:
(a) Weak acid and its salt.
(b) Weak base and its salt.
17. What is pH? Give its importance and usefulness.
18. What do you mean by solubility product? What is true solubility product?
19. Give an expression for the solubility product of the salt A x
B y
.
20. Discuss the effect of common ion on solubility product.