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The D-And-f-Block Elements

Question
CBSEENCH12007112
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Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with:
(a) iodide    (b) iron (II) solution and     (c) H2S.

Solution

Potassium dichromate, K2Cr2O7 is a strong oxidising agent and is used as a primary standard in volumetric analysis involving oxidation of iodides, ferrous ion and S2– ions etc. In acidic solution, its oxidising action can be represented as follows:
Cr2O72– + 14H+ + 6e– → 2Cr3+ + 7H2O;
(E+ = 1.33 V)

(a)    It oxidises potassium iodide to iodine.
Cr2O72– + 14H+ 61– → 2Cr3 + 7H2O + 3I2

(b)    It oxidises iron(II) salt to iron (III) salt
Cr2O72– + 14H+ + 6Fe2+ → 2Cr3+ + 6Fe3+ + 7H2O

(c)    It oxidises H2S to S
Cr2O72– + 8H+ + 3H2S → 2Cr3+ + 7H2O + 3S

 

Some More Questions From The d-And-f-Block Elements Chapter

The E° (M2+/M) value for copper is positive (+ 0.34 V). What is possibility the reason for this? 

How would you account for the irregular variation of ionisation enthalpies (first and second) in the first series of the transition elements?

Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?

Which is a stronger reducing agent Cr2+ or Fe2+ and why?

Explain why Cu+ ion is not stable in aqueous solutions?

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

The outer electronic configuration of copper is 3d10 4s1, yet it is considered transition element. Why?

Why the melting points of transition elements are high?

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