9701 MCQ Solution 56

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.