Question

When determining the amount of an oxidant present by titration, you can use iodine and starch as an indicator.

First, the oxidant, like hypochlorite, oxidizes

Choose...

neutral iodine into iodide ion

iodide ion into neutral iodine

iodate polyatomic ion into iodide ion

. When starch and iodine are both present, the solution is

Choose...

blue-black

brownish yellow

clear

.

During the titration, the titrant, like thiosulfate, reduces the

Choose...

iodide ion into iodate polyatomic ion

neutral iodine into iodide ion

iodide ion into neutral iodine

. When the iodine has completely reacted at the endpoint of the titration, the solution should become

Choose...

clear

blue-black

brownish yellow

.

Answer 1

When determining the amount of an oxidant present by titration, you can use iodine and starch as an indicator.

• First, the oxidant, like hypochlorite, oxidizes Iodide ion into neutral iodine :- ClO^- + 2I^- + 2H⁺ → Cl^- + I₂ + H₂O

• When starch and iodine are both present, the solution is blue-black :- starch is a polysaccharide consisting two kinds of molecules amylose and amylopectin . Amylose in starch is responsible for the formation of Blue-black colour in presence of Iodine.

• During the titration, the titrant, like thiosulfate, reduces the

  neutral iodine into iodide ion :- I₂ + 2S₂O₃^2- → 2I^- + S₄O₆^2-

• When the iodine has completely reacted at the endpoint of the titration, the solution should become clear .