9701 MCQ Solution 56

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Question 56: [Physical > Electrochemistry]
Chlorine compounds show oxidation states ranging from –1 to +7
What are the reagent(s) and conditions necessary for the oxidation of elemental chlorine into a compound containing chlorine in the +5 oxidation state?
A AgNO3(aq) followed by NH3(aq) at room temperature
B concentrated H2SO4 at room temperature
C cold dilute NaOH(aq)
D hot concentrated NaOH(aq)
Reference: Past Exam Paper -June 2003 Paper 1 Q16.


Solution 56:
Answer: D.
A cannot be answer because once AgNO3 reacts with elemental chlorine it will form AgCl in which chlorine is having a -1 charge. followed by aqueous ammonia then ammonia will form a co-ordinate bond with Ag and ammonia will act as a lignand the overall product is a complex ion and chlorine still has a -1 charge. [Ag(NH3)2]+ Cl-. because of the complex ions the solution is soluble in aqueous ammonia.
B cannot be answer because there is no reaction
C cannot be answer because when elemental chlorine reacts with cold NaOH the overall reaction is :
2NaOH + Cl2= NaCl + NaClO + H2O. and there is no product here that has chlorine in the +5 oxidation state . in NaCl the chlorine is having a -1 and in the NaClO its having +1.
D is therefore the answer because the overall reaction of elemental chlorine with hot concentrated NaOH is:
3Cl2 + 6NaOH = 5NaCl + NaClO3 + 3H2O.
and therefore the oxidation state of cholrine in NaClO3 is +5.
+1 + x + (-6) = 0
x= 6-1
x=+5.

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