Qualitative and Quantitative Analysis of Organic Compounds MCQ Quiz in தமிழ் - Objective Question with Answer for Qualitative and Quantitative Analysis of Organic Compounds - இலவச PDF ஐப் பதிவிறக்கவும்

CONCEPT:

Scanning Electron Microscopy (SEM)

• Scanning electron microscopy (SEM) is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons.
• The electrons interact with atoms in the sample, producing various signals that can be detected and contain information about the surface topography and composition of the sample.

EXPLANATION:

• Scanning Electron Microscopy (SEM) is primarily used to obtain high-resolution images of the surface of materials.
  • It provides detailed information about the morphology and surface structure of the sample.
  • The electron beam scans the sample surface and the interactions between the electrons and the atoms generate signals that form an image.
• Other options such as crystal structure, binding nature, and particle size are typically not determined directly by SEM:
  • Crystal structure is usually analyzed using techniques like X-ray diffraction (XRD).
  • Binding nature can be studied using spectroscopic methods.
  • Particle size can be analyzed using techniques like dynamic light scattering (DLS) or transmission electron microscopy (TEM).

Therefore, the correct answer is option 1: Structure of material surface.

Concept:

Kjeldahl’s method is a widely used technique for estimating the nitrogen content in organic compounds. The procedure involves the digestion of the sample with concentrated sulfuric acid (H₂SO₄), where the organic nitrogen is converted to ammonium sulfate ((NH₄)₂SO₄).

Explanation:

Various chemicals are added during the digestion process for specific purposes. Potassium sulfate (K₂SO₄) plays a particular role in this method:

• The primary function of K₂SO₄ is to raise the boiling point of the digestion mixture. This allows the digestion temperature to be increased, leading to the efficient and complete breakdown of the organic material.

Conclusion:

In Kjeldahl’s method of estimation of nitrogen, K2SO₄ acts as: Boiling point elevator

Concept:

Distillation:

• It involves heating a liquid to create vapor and then cooling the vapor to create a liquid.

• Distillation separates components based on differences in their boiling points.

• It is commonly used in the purification of liquids and the separation of liquid mixtures.

• There are different types of distillation, including simple distillation, fractional distillation, and vacuum distillation, each suited for specific purposes.

• For distillation to effectively separate two liquids, they must differ in boiling points by at least 25°C.

Explanation:

Distillation leverages the boiling point difference between components in a mixture:

• When a mixture is heated, the component with the lower boiling point vaporizes first.

• The vapor is collected and cooled in a condenser to get a purified liquid (distillate).

• If the boiling points of the components are close (<25°C), fractional distillation with a longer fractionating column is used to achieve better separation.

• Vacuum distillation is employed for substances with very high boiling points to lower the boiling temperatures by reducing the ambient pressure.

• Efficient separation relies on maintaining accurate temperature control and steady heating rates.

Conclusion:

Distillation is effective for separating liquids which differ in the boiling point by at least 25°C.

Concept

When an inorganic salt is heated with ethyl alcohol and concentrated sulfuric acid (H₂SO₄), the resulting vapors may produce a characteristic colored flame upon ignition. Some key points about this reaction are:

1. Concentrated H₂SO₄ acts as a dehydrating agent and facilitates the reaction by breaking down the salt and releasing volatile compounds.

2. Ethyl alcohol (ethanol) is used as a medium, which can produce volatile esters and other compounds depending on the anion present in the salt.

3. The color of the flame is a qualitative test, useful for identifying specific anions due to their distinct emission spectra when excited by heat.

4. A green-edged flame is a specific indicator of the presence of borate ions (BO₃^3-), which form volatile boron compounds that burn with a green edge.

5. This flame test is a quick and effective way to identify certain anions in the laboratory without needing sophisticated equipment.

Explanation:

The characteristic flame colors associated with each of the given anions are:

1. F^- (Fluoride): Fluoride does not produce a characteristic flame color.

2. C₂O₄^2- (Oxalate): Oxalate ion does not typically produce a colored flame.

3. BO₃^3- (Borate): Borate produces a green-edged flame when heated with ethyl alcohol and concentrated sulfuric acid due to the formation of volatile boron compounds.

4. ClO₃^- (Chlorate): Chlorate ion can produce a violet or purple flame but not green-edged.

Conclusion:

The presence of a green-edged flame upon heating an inorganic salt with ethyl alcohol and concentrated H₂SO₄ indicates the presence of: BO₃^3-

Concept:

When a solution of Na₂C₂O₄ (sodium oxalate) is added to a solution containing various metal ions, it can result in the formation of insoluble oxalates. Important aspects to consider:

• Sodium oxalate can react with metal cations such as Ba²⁺, Sr²⁺, and Ca²⁺ to form insoluble oxalates.

• The solubility product (K_sp) values of the metal oxalates determine the extent to which each cation will precipitate.

Explanation:

• Ba²⁺: Barium oxalate (BaC₂O₄) has a very low solubility product, so Ba²⁺ ions will precipitate readily.

  • \(\mathrm{Ba}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}+\mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \longrightarrow \underset{\text { white ppt. }}{\mathrm{BaC}_{2} \mathrm{O}_{4}}+2 \mathrm{CH}_{3} \mathrm{COONa}\)

• Sr²⁺: Strontium oxalate (SrC₂O₄) is also quite insoluble and will precipitate out of solution.

  • \(\mathrm{Sn}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}+\mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \longrightarrow \underset{\text { white ppt. }}{\mathrm{SrC}_{2} \mathrm{O}_{4}}+2 \mathrm{CH}_{3} \mathrm{COONa}\)

• Ca²⁺: Calcium oxalate (CaC₂O₄) is similarly insoluble and will form a precipitate.

  • \(\mathrm{Ca}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}+\mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \longrightarrow \underset{\text { white ppt. }}{\mathrm{CaC}_{2} \mathrm{O}_{4}}+2 \mathrm{CH}_{3} \mathrm{COONa}\)

Thus, the addition of Na₂C₂O₄ to a solution containing Ba²⁺, Sr²⁺, and Ca²⁺ ions will result in the formation of their respective oxalates, all of which are insoluble and will precipitate out of the solution.

Conclusion:

A solution of Na₂C₂O₄, when added to a solution containing Ba²⁺, Sr²⁺ and Ca²⁺ ions, will precipitate are: Ba²⁺, Sr²⁺, and Ca²⁺ ions

CONCEPT:

Qualitative Analysis of Nickel Ions

• In qualitative inorganic analysis, specific reagents are used to identify the presence of certain metal ions based on the formation of characteristic precipitates.
• Nickel(II) ions (Ni²⁺) can be detected using dimethyl glyoxime (dmg), which forms a distinctive red precipitate with Ni²⁺ in a basic medium.

EXPLANATION:

• When dimethyl glyoxime is added to a solution containing Ni²⁺ ions in a basic medium, a chelation reaction occurs, forming a bright red precipitate.
• The reaction can be represented as follows:

  Ni²⁺ + 2dmg^- → Ni(dmg)₂

  • Here, Ni²⁺ is the nickel ion.
  • dmg^- is the dimethyl glyoxime anion.
  • Ni(dmg)₂ is the red chelate complex formed.
• This reaction is highly specific and is used as a qualitative test for the presence of nickel ions because of the distinct color change to a brilliant red precipitate.

Therefore, the reagent which gives a brilliant red precipitate with Nickel ions in a basic medium is dimethyl glyoxime (option 4).

CONCEPT:

Identifying Cations Using Precipitating Reagents

• NH₄Cl + NH₄OH: This combination is used to precipitate cations like Al³⁺.
• NH₄OH + Na₂CO₃: Used to precipitate alkaline earth metals such as Sr²⁺.
• NH₄OH + NH₄Cl + H₂S gas: This combination is used to precipitate metal sulfides such as Pb²⁺.
• dilute HCl: Used to precipitate cations such as Mn²⁺.

Explanation:-

List I contains reagents and conditions for precipitation.

List II contains cations that can be precipitated by the reagents and conditions in List I.

• A. NH₄Cl + NH₄OH  -- III. Al³⁺
• B. NH₄OH + Na₂CO₃  -- IV. Sr²⁺
• C. NH₄OH + NH₄Cl + H₂S gas  -- II. Pb²⁺
• D. dilute HCl  -- I. Mn²⁺

The correct answer is A-III, B-IV, C-II, D-I

CONCEPT:

Purification Methods for Organic Compounds

• Vacuum Distillation:
  • Used for compounds that decompose at their normal boiling point. Lowering the pressure allows the compound to boil at a lower temperature, avoiding decomposition.
• Steam Distillation:
  • Used for compounds that are immiscible with water and have a sufficiently high vapor pressure at the boiling point of water.
• Azeotropic Distillation:
  • Used to separate mixtures that form an azeotrope, which is a mixture with a constant boiling point that cannot be separated by simple distillation.
• Mixed Melting Point:
  • Used to check the purity of an organic compound. A pure compound will have the same melting point when mixed with a small amount of the same compound.

Explanation:-

• A. Correct. Glycerol decomposes at its normal boiling point, so it is purified by vacuum distillation.
• B. Incorrect. Aniline is actually purified by steam distillation because it is immiscible in water, not miscible.
• C. Correct. Ethanol forms an azeotrope with water, so they can be separated by azeotropic distillation.
• D. Correct. A pure organic compound will have the same melting point when mixed with the same compound.

The most appropriate answer is  A, C, D only.

CONCEPT:

Preparation of Mohr's Salt

• Mohr's salt is a double salt with the chemical formula FeSO₄·(NH₄)₂SO₄·6H₂O.
• During the preparation of Mohr's salt, it is important to maintain the Fe²⁺ ions in the ferrous state by preventing their oxidation and hydrolysis.
• Adding dilute sulfuric acid (H₂SO₄) helps in preventing the hydrolysis of ferrous sulfate and keeps the solution acidic.

EXPLANATION:

Fe+2 ions undergoes hydrolysis, therefore while preparing aqueous solution of ferrous sulphate and ammonium sulphate in water dilute sulphuric acid is added to prevent hydrolysis of ferrous sulphate.

• Hydrolysis of ferrous sulfate can lead to the formation of Fe(OH)₂, which can precipitate out of the solution.
• Dilute sulfuric acid prevents this hydrolysis by maintaining an acidic environment, which keeps the ferrous ions in solution.

The correct answer is 1) prevent the hydrolysis of ferrous sulphate.

CONCEPT:

Flame Test for Metal Ions

• The flame test is a qualitative analysis technique used to detect the presence of certain metal ions based on the color they produce in a flame.
• Different metal ions produce characteristic colors when heated in a flame due to the excitation of electrons and the subsequent emission of light at specific wavelengths.

Key Points

• Sr²⁺ (Strontium Ion):
  • Produces a crimson (red) flame.
• Ba²⁺ (Barium Ion):
  • Produces a green flame.
• Ca²⁺ (Calcium Ion):
  • Produces a brick-red flame.
• Cu²⁺ (Copper Ion):
  • Produces a green or blue-green flame.
• Zn²⁺ (Zinc Ion):
  • Produces a bluish-green flame, but this is often faint and not always reliable for identification.
• Co²⁺ (Cobalt Ion):
  • Does not produce a characteristic flame color and is not typically identified by flame test.
• Fe²⁺ (Iron Ion):
  • Does not produce a characteristic flame color and is not typically identified by flame test.

Conclusion:-

The metal ions that can be characterized by the flame test from the given list are:

Sr²⁺, Ba²⁺, Ca²⁺, and Cu²⁺. Total number of metal ions characterized by the flame test = 4