Qualitative Analysis of Organic Compounds Question And Answers – NEET General Organic Chemistry

Qualitative Analysis Of Organic Compounds

Question 1. Na ₂S+Na ₂ [Fe(CN) ₅NO]→Purple color. It is due to

1. Na ₄[Fe(CN) ₃NOS]
2. Na ₃[Fe(CN) ₅NOS]
3. Na ₄[Fe(CN) ₅NO]
4. Na ₄[Fe(CN) ₅NOS]

Answer: 4. Na₄ [Fe(CN)₅NOS]

Read And Learn More: NEET General Organic Chemistry Notes, Question And Answers

Question 2. For the estimation of sulfur in an organic compound, fuming nitric acid is used to convert sulfur into

1. SO₂
2. H₂S
3. H₂SO₃
4. H₂SO₄

Answer: 4. H₂SO₄

Solution: In this method, a known quantity of organic compounds is heated with either fuming nitric acid or sodium peroxide in a hard glass tube called the Carius tube. The sulfur present in the compound is oxidized to form sulphuric acid.

Question 3. The presence of carbon in an organic compound is detected by heating it with

1. Sodium metal to convert it into NaCN
2. CaO to convert it into CO which burns with a blue flame
3. CuO to convert it into CO₂ which turns lime water milky
4. Cu wire to give a bluish-green flame

Answer: 3. CuO converts it into CO₂ which turns lime water into milky

Solution: The organic compound is mixed with dry copper oxide (CuO) and heated in a hard glass tube. The products of the reaction are passed over (white) anhydrous copper sulfate and then bubbled through lime water. If copper sulfate turns blue due to the formation of CuSO₂.5H₂O (by water vapor) then the compound contains hydrogen. If lime water turns milky by CO₂, then the compound contains carbon.

Question 4. Detection of sulfur in sodium extract is done by

1. Lead acetate
2. Sodium nitroprusside
3. Both (1) and (2)
4. None of these

Answer: 3. Both (1) and (2)

Solution: Detection of sulfur in sodium extract is done by lead acetate and sodium nitroprusside

⇒ \(
\mathrm{Na}_2 \mathrm{~S}+\left(\mathrm{CH}_3 \mathrm{COO}\right)_2 \mathrm{~Pb} \rightarrow \mathrm{PbS}+2 \mathrm{CH}_3 \mathrm{COONa}
lead acetate black ppt.\)

⇒ \(\begin{aligned}
&\mathrm{Na}_2 \mathrm{~S}+\mathrm{Na}_2\left[\mathrm{Fe}(\mathrm{CN})_5 \mathrm{NO}\right] \rightarrow \mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_5 \mathrm{NOS}\right] \\
& \text { Sodium nitroprusside sodium thionitroprusside } \\
& \text { (Purple colour) } \\
&
\end{aligned}
\)

Question 5. In Lassaigne’s solution, pink/violet coloration is produced when sodium nitroprusside solution is added. It indicates the presence of

1. Sulfur
2. Nitrogen
3. Chlorine
4. None of these

Answer: 1. Sulfur

Solution:

\(\mathrm{Na}_2 \mathrm{~S}+\mathrm{Na}_2\left[\mathrm{Fe}(\mathrm{CN})_5 \mathrm{NO}\right] \rightarrow \underset{\text { (violet color) }}{\mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_5 \mathrm{NOS}\right]}\)

Question 6. Lassaigne’s test is not used for the detection of

1. Carbon
2. Halogens
3. Nitrogen
4. Sulfur

Answer: 1. Carbon

Solution: Lassaigne’s test is used for the detection of halogens, nitrogen, and sulfur.

Question 7. Red color complex ion formed on adding FeCl₃ to sodium extract when N and S both are present in the organic compound is

1. [Fe(CN)₆]^4-
2. [Fe(CNS)]²⁺
3. [Fe(CNS)₂]⁺
4. [Fe(CN)₆]^3-

Answer: 2. [Fe(CNS)]²⁺

Solution: When N and S both are present in the organic compound, then a red color complex ion of [Fe(CNS)]²⁺ is formed on adding FeCl₃ to sodium extract

\(\mathrm{NaCNS}+\mathrm{FeCl}_3 \rightarrow[\mathrm{Fe}(\mathrm{SCN})] \mathrm{Cl}_2+\mathrm{NaCl}\)

blood red color

Question 8. The sodium extract of an organic compound on acidification with acetic acid and the addition of lead acetate solution gives a black precipitate. The organic compound contains

1. Nitrogen
2. Halogen
3. Sulfur
4. Phosphorus

Answer: 3. Sulfur

Solution: The organic compounds are fused with Na metal, and Na₂S is formed which is tested as it reacts with lead acetate and forms a black ppt. of PbS

Na₂S+(CH₃COO)₂Pb→ PbS +2CH₃COONa

black ppt

Question 9. An organic compound that produces a bluish-colored flame on heating in the presence of copper is

1. Chlorobenzene
2. Benzaldehyde
3. Aniline
4. Benzoic acid

Answer: 1. Chlorobenzene

Solution: Halogen-containing compounds (C₆H₅Cl)when placed in a flame give green to blue flame in the presence of copper.

Question 10. Which of the following statements is wrong?

1. Using Lassaigne’s test nitrogen and sulfur present in the organic compound can be tested.
2. Using Bilstein’s test the presence of halogen in a compound can be tested
3. In Lassaigne’s filtrate, the nitrogen present in the organic compound is converted into NaCN
4. In the estimation of carbon, an organic compound is heated with CaO in a combustion tube

Answer: 3. In Lassaigne’s filtrate the nitrogen present in the organic compound is converted into NaCN

Solution: Statement 3. is wrong.

Question 11. Amongst the following, the total number of compounds soluble in aqueous NaOH is

1. 1
2. 2
3. 3
4. 4

Answer: 4. 4

Solution:

are soluble in aq. NaOH. Benzylic alcohol is less acidic than water so is not soluble in aq. NaOH,

Question 12. Acidified sodium fusion extract in addition to ferric chloride solution gives blood red coloration which confirms the presence of

1. S and Cl
2. N and S
3. N
4. S

Answer: 2. N and S

Solution: Acidified sodium fusion extract in addition to ferric chloride solution gives blood-red coloration, which confirms the presence of N and S.

\(3 \mathrm{NaCNS}+\mathrm{aq} \cdot \mathrm{FeCl}_3 \longrightarrow \mathrm{Fe}(\mathrm{CNS})_3+3 \mathrm{NaCl}\)

red (Ferric thiocyanide)

Question 13. Select the correct statement about the detection of sulfur in the organic compounds

1. Sulfur present in the organic compound on fusion with sodium is converted to Na₂S₂O₃
2. FeCl₃ gives a purple color when added to the sodium fusion extract
3. Sodium nitroprusside is used to detect the presence of sulfur
4. All of the above

Answer: 3. Sodium nitroprusside is used to detect the presence of sulfur

Solution: Sulfur is present in the sodium extract in the form of sodium sulfide (Na₂S) FeCl₃ gives blood red color with sodium extract containing N and S.

Question 14. The compound which forms one monochloride product when treated with chlorine is:

1. n-pentane
2. Isopentane
3. neo-pentane
4. None of these

Answer: 3. neo-pentane

Solution: Neopentane has only one type of replaceable hydrogen.

The compound which forms one monochloride product when treated with chlorine is neo-pentane

Question 15. The compound formed for the positive test for nitrogen with Lassaigne’s solution of an organic compound is

1. Fe₄[Fe(CN)₆]₃
2. Na₃[Fe(CN)₆]
3. Fe(CN)₃
4. Na₄[Fe(CN)₂NOS]

Answer: 1. Fe₄[Fe(CN)₆]₃

Solution: If nitrogen is present in the organic compounds, then sodium extract contains NaCN.

\(\begin{gathered}
\mathrm{Na}+\mathrm{C}+\mathrm{N} \stackrel{\text { Puse }}{\longrightarrow} \mathrm{NaCN} \\
\mathrm{FeSO}_4+6 \mathrm{NaCN} \rightarrow \mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]+\mathrm{Na}_2 \mathrm{SO}_4
\end{gathered}\)

A change to Prussian blue Fe4[Fe(CN)6 ]3 on reaction with FeCl3.

\(4 \mathrm{FeCl}_3+3 \mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right] \rightarrow \mathrm{Fe}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]_3+12 \mathrm{NaCl}\)

Question 16. Which of the following complex formations indicates the presence of sulfur in the organic compound when sodium nitroprusside is added to the sodium extract of the compound?

1. Fe₄[Fe(CN)₆]₃
2. Na₂[Fe(NO) (CN)₅]
3. Fe₄(CNS)₃
4. Na₄[Fe(CN)₅NOS]

Answer: 4. Na₄[Fe(CN)₅NOS]

Solution: The formation of sodium thio nitroprusside (blue) shows the presence of sulfur.

\(
\mathrm{Na}_2 \mathrm{~S}+\mathrm{Na}_2\left[\mathrm{Fe}(\mathrm{NO})(\mathrm{CN})_5\right] \rightarrow \mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_5 \mathrm{NOS}\right]\)

sodium nitroprusside sodium thionitroprusside purple

Question 17. The treatment of CH3MgX with CH3C≡C—H produces:

CH₄

CH₃—CH = CH₂

CH₃C ≡ C – CH₃

Answer: 1. CH₄

Solution:

\(\mathrm{CH}_3 \mathrm{MgX}+\mathrm{CH}_3 \mathrm{C} \equiv \mathrm{C}-\mathrm{H}_{\text {Acidic }} \rightarrow \mathrm{CH}_4+\mathrm{CH}_3 \mathrm{C} \equiv \mathrm{C} . \mathrm{MgX}\).

Question 18. The copper wire test of halogens is known as

1. Liebig’s test
2. Lassaigen’s test
3. Fusion test
4. Beilstein’s test

Answer: 4. Beilstein’s test

Solution: The Beilstein test is a simple qualitative chemical test for organic halides. It was developed by Friedrich Konrad Beilstein. A copper wire is cleaned and heated in a Bunsen burner flame to form a coating of copper (2) oxide.

Question 19. Lassaigne’s test is used for the detection of

1. Carbon only
2. Hydrogen only
3. Oxygen only
4. Nitrogen, sulfur, and halogens

Answer: 4. Nitrogen, sulfur and halogens

Solution: The sodium fusion test, or Lassaigne’s test, is used in the elemental analysis for the qualitative determination of the presence of foreign elements, namely halogens, nitrogen, and sulfur, in an organic compound

Question 20. During the AgNO₃ test for the detection of halogens, sodium extract is boiled with a few drops of conc. HNO₃ to decompose

1. NaCN
2. Na₂S
3. Both (1) and (2)
4. None of these

Answer: 3. Both (1) and (2)

Solution:

\(\begin{array}{r}
\underset{\mathrm{NaCN}}{\stackrel{\Delta}{\Delta}}+\mathrm{HNO}_3 \stackrel{\Delta}{\rightarrow} \mathrm{HCN} \uparrow+\mathrm{NaNO}_2 \\
\mathrm{Na}_2 \mathrm{~S}+\mathrm{HNO}_3 \stackrel{\mathrm{H}}{\rightarrow} \mathrm{S} \uparrow+2 \mathrm{NaNO}_3
\end{array}\)

When an organic compound containing both nitrogen and sulfur is fused with sodium, sodium thiocyanate is formed.

Question 21. The sodium extract of an organic compound on boiling with HNO₃ and the addition of ammonium molybdate of solution gives a yellow precipitate. The compound contains

1. Nitrogen
2. Phosphorus
3. Sulfur
4. Chlorine

Answer: 2. Phosphorus

Solution:

Na₃PO₄+3HNO₃→H₃PO₄+3NaNO₃

sod. extract

H₃PO₄+12(NH₄)₂MoO₂ + 21HNO₃→(NH₄)₃PO₄.12MoO₃+21NH₄NO₃+12H₂O

The sodium extract of an organic compound on boiling with HNO₃ and the addition of ammonium molybdate of solution gives a yellow precipitate. The compound contains Phosphorus

Question 22. In Lassaigne’s test, a blue color is obtained if the organic compound contains nitrogen. The blue color is due to

K₄[Fe(CN)₆]

Fe₄[Fe(CN)₆]₃

Na₃[Fe(CN)₆]

Cu₂[Fe(CN)₆]

Answer: 2. Fe₄[Fe(CN)₆]₃

Solution: In Lassaigne’s test, a blue color is obtained if the organic compound contains nitrogen. The blue color is due to ferri-ferrocyanide i.e., Fe₄[Fe(CN)₆]₃.

Question 23. Qualitative test of halogens in an organic compound is done by

1. Fleming’s test
2. Beilstein test
3. Baeyer’s test
4. Fehling’s test

Answer: 2. Beilstein test

Solution: Halogens can be identified in organic compounds by Beilstein-test.

Question 24. During the fusion of an organic compound with sodium metal, the nitrogen of the compound is converted into

1. NaNO₂
2. NaNH₂
3. NaCN
4. NaNC

Answer: 3. NaCN

Solution: When an organic compound is fused with sodium metal, the nitrogen of the compound is converted into sodium cyanide as

Na + C + N→ NaCN

Question 25. Zn—Cu couple used as a reducing agent is:

1. A mixture of Zn and Cu powder
2. Copper deposited on granulated zinc
3. Zn deposited on copper fillings
4. A rod half made of copper and half made of zinc

Answer: 2. Copper deposited on granulated zinc

Solution: It is a fact.

Question 26. Detection of phosphorus in the compound can be done by its conversion into phosphate. The reagent to identify phosphate ions is

1. Sodium nitroprusside
2. Ammonium molybdate
3. Potassium ferrocyanide
4. Potassium ferricyanide

Answer: 2.

Solution: Detection of phosphorus in the organic compound can be done by its conversion into phosphate. The ammonium molybdate is used to identify phosphate ion

\(\begin{gathered}
\mathrm{Na}_3 \mathrm{PO}_4+3 \mathrm{HNO}_3 \rightarrow \mathrm{H}_3 \mathrm{PO}_4 3 \mathrm{NaNO}_3 \\
\mathrm{H}_3 \mathrm{PO}_4+12\left(\mathrm{NH}_4\right)_2 \mathrm{MoO}_4+21 \mathrm{HNO}_3 \stackrel{\Delta}{\rightarrow}\left(\mathrm{NH}_4\right)_3 \mathrm{PO}_4 \cdot 12 \mathrm{MoO}_3+21 \mathrm{NH}_4 \mathrm{NO}_3+12 \mathrm{H}_2 \mathrm{O}
\end{gathered}\)

Question 27. The Lassaigne’s extract is boiled with dilute HNO3 before testing for halogens because

1. AgCN is soluble in HNO₃
2. Silver halides are soluble in HNO₃
3. Na₂S and NaCN are decomposed by HNO₂
4. Ag₂S is soluble in HNO₃

Answer: 3. Na₂S and NaCN are decomposed by HNO₃

Solution: HNO₃ is added to decompose Na₂S and NaCN if present

Na₂S+2HNO₃→ 2NaNO₃+H2S↑

NaCN+HNO₃→ NaNO₃+HCN↑

Question 28. In the detection of sulfur present in an organic compound, sodium nitroprusside solution is added to the sodium extract. The formation of the violet color is due to

1. Na₃Fe(CN)₆
2. Na₄ [Fe(CN)₅NOS]
3. Fe(CNS)₃
4. None of these

Answer: 2. Na₄ [Fe(CN)₅NOS]

Solution:

Fe(CNS)₃ is red in color and is formed when both N and S are present in the organic compound

Na₂S+Na₂ [Fe(CN)₅NO]→[Na₄Fe(C)₅NOS] from organic violet color compound

Question 29. The Beilstein test for organic compounds is used to detect

1. Nitrogen
2. Sulfur
3. Carbon
4. Halogens

Answer: 4. Halogens

Solution: The Beilstein test is used to detect halogens in organic compounds.

Question 30. Lassaigne’s test for the detection of nitrogen fails in

1. H₂N-CO-NHNH₂.HCl
2. NH₂-NH₂.HCl
3. NH₂-CO-NH₂
4. C₆H₅-NH-NH₂.HCl

Answer: 2. NH₂-NH₂.HCl

Solution: Lassaigne’s test is given by those nitrogenous compounds in which carbon is also present along with nitrogen. In NH₂.NH₂.HCl, Carbon is absent, so it does not give Lassaigne’s test.

Question 31. Nitrogen-containing organic compounds when fused with sodium form

1. Sodium azide
2. Sodium cyanide
3. Sodamide
4. Sodium cyanate

Answer: 2. Sodium cyanide

Solution: An organic compound containing nitrogen is fused with a small piece of sodium metal to form NaCN.

\(\mathrm{Na}+\underbrace{\mathrm{C}+\mathrm{N}} \rightarrow \mathrm{NaCN}\)

Question 32. Which of the following elements can’t be detected by direct tests?

1. N
2. O
3. S
4. Br

Answer: 2. N

Solution: Oxygen cannot be detected by direct test because oxygen is present in the atmosphere and all tests are carried in the atmosphere of oxygen.

Question 33. The Prussian blue color obtained during the test of nitrogen by Lassaigne’s test is due to the formation of

1. Fe₄[Fe(CN)₆]₃
2. Na₄[Fe(CN)₆]
3. Fe₃[Fe(CN)₆]₄
4. Fe₂[Fe(CN)₆]

Answer: 1. Fe₄[Fe(CN)₆]₃

Solution: The treatment with FeCl3 yields ferric ferrocyanide which has bluish green or Prussian blue coloration 3Na₄ [Fe(CN)₆]+4FeCl₃→ Fe₄ [Fe(CN)₆ ]₃

Question 34. Which of the organic compounds will give a red color in Lassaigne’s test?

1. NaCNS
2. 
3. O
4. None of these

Answer:

2.

Solution: In the lasagne’s test, if an organic compound consists of both N and S, then a red color is obtained by adding aqueous FeCl3 to the sodium extract. “B” contains both N and S hence, it will give red color in Lassaigne’s test

\(
\mathrm{NaCNS}+\mathrm{FeCl}_3 \longrightarrow[\mathrm{Fe}(\mathrm{SCN})] \mathrm{Cl}_2+\mathrm{NaCl}
Blood red color\)

Question 35. Sodium nitroprusside when added to an alkaline solution of sulfide ions produces a coloration

1. Red
2. Brown
3. Blue
4. Purple

Answer: 4. Purple

Solution: Sodium nitroprusside when added to an alkaline solution of sulfide ions produces a purple-colored complex which is Na₄[Fe(CN)₅NOS]. The total amount of sodium per molecule in this purple-colored complex is 4.

Question 36. Which of the following statements is not applicable to the Beilstein test?

1. Bluish-green flame is due to the formation of volatile cupric halides
2. It does not tell us as to which halogen is present in the organic compound
3. It is a very sensitive test but can be easily performed
4. It is a sure test for the presence of the halogens

Answer: 4. It is a sure test for the presence of the halogens

Solution: If an organic compound gives a blue or green color at the tip of red-hot copper wire, this indicates the presence of halogens in the compound. However, compounds like urea, thiourea, etc. also give blue or green color in this test even in the absence of halogens, thus, it is not a sure test for halogens

Question 37. In Lassaigne’s test, the organic compound is fused with a piece of sodium metal in order to

1. Increase the ionization of the compound
2. Decrease the melting point of the compound
3. Increase the reactivity of the compound
4. Convert the covalent compound into a mixture of ionic compounds

Answer: 4. Convert the covalent compound into a mixture of ionic compounds

Solution: In Lassaigne’s Test, the organic compound is fused with a piece of Na metal in order to convert these elements to water-soluble compounds. Basically, to convert covalent compounds into a mixture of ionic compounds that are water soluble and can be detected by simple chemical tests.

Assertion-Reasoning Type:

The question contains Statement 1(Assertion) and Statement 2(Reason). Each Question has 4 choices (1), (2), (3), and (4) out of which Only One is correct.

1. Statement 1 is True; Statement 2 is True; Statement 2 is a correct explanation for Statement 1
2. Statement 1 is True; Statement 2 is True; Statement 2 is not the correct explanation for Statement 1
3. Statement 1 is True, Statement 2 is False
4. Statement 1 is False, Statement 2 is True

Question 38.

1. Statement 1: Lassaigne’s test is for nitrogen only
2. Statement 2: If halogens are present in the organic compound, they react with sodium to form sodium halide which dissolves in the water.

Answer: 4. Statement 1 is False, Statement 2 is True

Solution: