Question

| 19. The ratio of Fe3+ and Fe2+ in Fe0.9S1.0 is
(1) 0.28
(2) 0.5
(3) 2
(4) 4​

Answer 1

answer : option (1)0.28

explanation : we have to find ratio of Fe³+ and Fe²+ in $Fe_{0.9}S_{1.0}$

Let us consider that total number of Fe atoms = 90 then, number of S-atoms = 100.

in 90 atoms of Fe, x atoms are in Fe²+ form and (90 - x) atoms are in Fe³+ form.

for Fe²+ form,

chemical formula of sulphide = FeS

Fe and S are in 1 : 1 ratio.

so, number of S atoms will be also x.

for Fe³+ form,

chemical formula of sulphide = Fe2S3

Fe and S are in 2 : 3 ratio.

so, number of S-atoms will be 3(90 - x)/2 = 1.5(90 - x)

now, number of S-atoms joined with Fe²+ + number of S-atoms joined with Fe³+ = 100

or, x + 1.5(90 - x) = 100

or, x + 135 - 1.5x = 100

or, 35 = 0.5x

or, 70 = x

and 90 - x = 20

so, ratio of Fe³+ and Fe²+ = 20/70 = 0.28