What is the chemical formula of the reddish-brown vapors evolved during a positive Chromyl Chloride test, and what is the oxidation state of chromium in it?

What is the chemical formula of the reddish-brown vapors evolved during a positive Chromyl Chloride test, and what is the oxidation state of chromium in it? +

Correct Answer

Reddish-brown vapors are Chromyl chloride (CrO₂Cl₂).
The oxidation state of chromium is +6.

Why?

In the Chromyl Chloride Test, a chloride-containing salt is heated with potassium dichromate (K₂Cr₂O₇) and concentrated H₂SO₄. If chloride ions are present, reddish-brown vapours of chromyl chloride are produced.

CrO₂Cl₂

To calculate the oxidation state of Cr: Let oxidation state of Cr = x. Oxygen has −2 oxidation state and chlorine has −1.

x + 2(−2) + 2(−1) = 0
x − 4 − 2 = 0
x = +6

Therefore, chromium is in the +6 oxidation state.

Chromyl Chloride Test — Key Reaction

A simplified representation is:

Cr₂O₇²⁻ + 4Cl⁻ + 6H⁺ → 2CrO₂Cl₂ + 3H₂O

The characteristic reddish-brown vapours indicate a positive Chromyl Chloride Test for chloride.

Important Exam Point

Reddish-brown vapour → CrO₂Cl₂ → Cr = +6

30 Related MCQs with Solutions

1. The reddish-brown vapours in the Chromyl Chloride Test are:

A. CrCl₃

B. CrO₂Cl₂

C. CrO₃

D. CrCl₂

Answer: B. CrO₂Cl₂

2. The common name of CrO₂Cl₂ is:

A. Chromium chloride

B. Chromyl chloride

C. Chromous chloride

D. Chromic chloride

Answer: B. Chromyl chloride

3. Oxidation state of chromium in CrO₂Cl₂ is:

A. +2

B. +3

C. +5

D. +6

Answer: D. +6

4. Which colour is characteristic of chromyl chloride vapours?

A. Green

B. Blue

C. Reddish-brown

D. Yellow

Answer: C. Reddish-brown

5. Chromyl Chloride Test is primarily used to detect:

A. Sulphate

B. Nitrate

C. Chloride

D. Carbonate

Answer: C. Chloride

6. The oxidising agent commonly used in the test is:

A. KMnO₄

B. K₂Cr₂O₇

C. NaOH

D. HCl

Answer: B. K₂Cr₂O₇

7. Which acid is used along with dichromate in the test?

A. Dilute HCl

B. Concentrated H₂SO₄

C. HNO₃

D. CH₃COOH

Answer: B. Concentrated H₂SO₄

8. Oxidation state of oxygen in CrO₂Cl₂ is:

A. −1

B. −2

C. +1

D. +2

Answer: B. −2

9. Oxidation state of chlorine in CrO₂Cl₂ is:

A. +1

B. 0

C. −1

D. +7

Answer: C. −1

10. In CrO₂Cl₂, the total contribution of oxygen to oxidation number is:

A. −2

B. −4

C. −6

D. +4

Answer: B. −4

11. Chromyl chloride has how many oxygen atoms?

A. 1

B. 2

C. 3

D. 4

Answer: B. 2

12. Chromyl chloride has how many chlorine atoms?

A. 1

B. 2

C. 3

D. 4

Answer: B. 2

13. The formula CrO₂Cl₂ is electrically:

A. +2 charged

B. −2 charged

C. Neutral

D. +6 charged

Answer: C. Neutral

14. The chromium species responsible for the reddish-brown vapour contains Cr in:

A. +2 state

B. +3 state

C. +6 state

D. 0 state

Answer: C. +6 state

15. Which ion is converted into chromyl chloride during the test?

A. Br⁻

B. I⁻

C. Cl⁻

D. SO₄²⁻

Answer: C. Cl⁻

16. A positive Chromyl Chloride Test gives:

A. Reddish-brown fumes

B. White precipitate only

C. Blue solution

D. Black precipitate

Answer: A. Reddish-brown fumes

17. Which chromium compound is used as the chromium source in the test?

A. K₂Cr₂O₇

B. CrCl₃

C. CrO

D. Cr₂O₃

Answer: A. K₂Cr₂O₇

18. The oxidation state of Cr in dichromate ion is:

A. +3

B. +4

C. +6

D. +7

Answer: C. +6

19. Which observation confirms chloride in the Chromyl Chloride Test?

A. Reddish-brown vapours

B. Green precipitate

C. Blue precipitate

D. No colour change

Answer: A

20. The correct formula is:

A. CrOCl₂

B. CrO₂Cl

C. CrO₂Cl₂

D. Cr₂OCl₂

Answer: C. CrO₂Cl₂

21. The oxidation state calculation for CrO₂Cl₂ is:

A. x − 4 − 2 = 0

B. x + 4 + 2 = 0

C. x − 2 + 2 = 0

D. x + 2 − 4 = 0

Answer: A

22. Chromium in +6 oxidation state belongs to:

A. Chromous state

B. Chromic state

C. High oxidation state

D. Zero state

Answer: C. High oxidation state

23. Chromyl chloride is best described as:

A. CrO₂Cl₂

B. CrCl₃

C. CrO₃

D. K₂Cr₂O₇

Answer: A

24. The colour of chromyl chloride vapour is mainly described as:

A. Reddish-brown

B. Violet

C. Pale green

D. Colourless

Answer: A

25. The Chromyl Chloride Test belongs to qualitative analysis of:

A. Anions

B. Cations only

C. Organic compounds only

D. Noble gases

Answer: A. Anions

26. Which oxidation state is common to Cr in both dichromate and chromyl chloride?

A. +2

B. +3

C. +6

D. +7

Answer: C. +6

27. If chloride is absent, the characteristic chromyl chloride vapour:

A. Should not be formed

B. Must always form

C. Becomes blue

D. Becomes green

Answer: A

28. Which element is present in chromyl chloride besides Cr, O and Cl?

A. Na

B. K

C. No additional element

D. S

Answer: C

29. Chromyl chloride is a useful test because its vapour has a:

A. Characteristic reddish-brown colour

B. Characteristic black colour

C. Characteristic blue precipitate

D. Characteristic white colour

Answer: A

30. The correct match is:

A. CrO₂Cl₂ — Cr(+3)

B. CrO₂Cl₂ — Cr(+6)

C. CrCl₃ — Cr(+6)

D. CrO₃ — Cr(+2)

Answer: B. CrO₂Cl₂ — Cr(+6)

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