Solutions/Answers to NCERT/CBSE CHEMISTRY Class 11(Class XI)textbook ...
7.71 What is the maximum concentration of equimolar solutions of ferrous.
NCERT/CBSE CHEMISTRY CLASS 11 textbook http://www.TutorBreeze.com Contact for Online Tutoring in Physics, Math, Chemistry, English, Accounts, MBA Solutions/Answers to NCERT/CBSE CHEMISTRY Class 11(Class XI)textbook CHAPTER SEVEN EQUILIBRIUM 7.71 What is the maximum concentration of equimolar solutions of ferrous sulphate and sodium sulphide so that when mixed in equal volumes, there is no precipitation of iron sulphide? (For iron sulphide, K sp = 6.3 × 10– 18). Solution:
Let the maximum concentration of ferrous sulphate and sodium sulphide be x M. x Thus for the combined solution we have halved molar concentrations( M). 2 The reaction is: FeS Fe2+ + S2At eqbm.:
x 2
x 2
We have,K SP = [Fe 2+ ][S2- ] =
x2 =6.3 ×10-18 4
Solving , x = 5.02 ×10−9 M
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NCERT/CBSE CHEMISTRY CLASS 11 textbook http://www.TutorBreeze.com Contact for Online Tutoring in Physics, Math, Chemistry, English, Accounts, MBA .70 The ionization constant of benzoic acid is 6.46 × 10–5 and K for silver benzoate sp is 2.5 × 10–13. How many times is silver benzoate more
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Let the solubility of silver benzoate in water be s. The reaction is: C6 H 5COOAg C6 H 5COO −1 +Ag + At eqbm.:
s
s
−1
+
We have,K SP = [C6 H 5COO ][Ag ] ⇒ 2.5 × 10−13 = s 2 Solving ,s=5.0 × 10-7 M Now in case of buffer of given pH, 3.19=-log[H + ] ⇒ [ H + ] = 10 −3.19 = Antilog(4.81)=6.457 ×10-4 Reaction for dissociation of benzoic acid is: C6 H 5COOH C6 H 5COO −1 +H + Concentration of hydrogen ions can be assumed to be constant as the solution is a buffer. Assume solubility in buffer solution to be s'. We have, Ka = ⇒
[C6 H 5COO −1 ][H + ] = 6.46 × 10−5 [C6 H 5 COOH] [C6 H 5 COOH] 6.457 ×10-4 = ≈ 10 [C6 H 5COO −1 ] 6.46 × 10−5 Now:
[Ag]+ = s ' = [C6 H 5COO −1 ] + [C6 H 5COOH ](These values are to be substituted from above). ⇒ s'=11[C6 H 5COO −1 ] s' 11 C6 H 5COOAg C6 H 5COO −1 +Ag + ⇒ [C6 H 5COO −1 ] =
At eqbm.:
s' 11
s'
s '2 = 1.66 × 10 −6 11 s' 1.66 × 10−6 Now ratio of solubilities= = = 3.32 s 5.0 × 10-7 Thus,silver benzoate is 3.32 times more soluble in a buffer of pH 3.19 ©TutorBreeze.com compared to its solubility in pure water. Now,k SP = [C6 H 5COO −1 ][Ag + ] =
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