Purification & Characterisation of Organic Compounds Flashcards for NEET — 20 cards

First 8 of 20 Purification & Characterisation of Organic Compounds flashcards

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1. Card 1 of 20

   What is the principle behind Crystallization?

   Hint: Think: temperature-dependent solubility

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   Answer

   It is based on the difference in the solubilities of the compound and the impurities in a suitable solvent. The impure compound dissolves at higher temperatures and crystallizes out upon cooling.

2. Card 2 of 20

   When is Fractional Distillation preferred over Simple Distillation?

   Hint: Relies on a specialized column

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   Answer

   Fractional distillation is used when the difference in boiling points of two miscible liquids is very small (less than $25^\circ\text{C}$ or $40\text{K}$). It uses a fractionating column to provide surfaces for repeated condensation and vaporization.

3. Card 3 of 20

   What is the principle of Steam Distillation and name a compound purified by it.

   Hint: Water vapor + organic vapor

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   Answer

   It is used for substances that are steam volatile but immiscible with water. The mixture boils when the sum of vapor pressures ($p_1 + p_2$) equals atmospheric pressure. Example: Aniline.

4. Card 4 of 20

   Define Retardation Factor ($R_f$) in Thin Layer Chromatography (TLC) and explain its components.

   Hint: Ratio of distances

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   Answer

   $R_f = \frac{x}{y}$

5. Card 5 of 20

   Why is Sodium Extract (Lassaigne's extract) prepared for qualitative analysis?

   Hint: Covalent to Ionic conversion

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   Answer

   Organic compounds are covalent. Fusing them with sodium metal converts the covalently bonded elements (N, S, Halogens) into ionic sodium salts ($\text{NaCN}$, $\text{Na}_2\text{S}$, $\text{NaX}$) which are water-soluble and detectable.

6. Card 6 of 20

   Name the complex formed and its color during the positive Lassaigne's test for Nitrogen.

   Hint: Iron (III) hexacyanoferrate (II)

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   Answer

   Prussian Blue color is formed due to the complex Ferriferrocyanide: $\text{Fe}_4[\text{Fe(CN)}_6]_3 \cdot x\text{H}_2\text{O}$.

7. Card 7 of 20

   What does a blood-red coloration in Lassaigne's test indicate?

   Hint: Thiocyanate formation

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   Answer

   It indicates the presence of BOTH Nitrogen and Sulphur in the organic compound. They form Sodium thiocyanate ($\text{NaSCN}$), which reacts with $\text{Fe}^{3+}$ to form the blood-red complex $[\text{Fe(SCN)}]^{2+}$.

8. Card 8 of 20

   Give the reagent and observation for the detection of Sulphur using Sodium Nitroprusside.

   Hint: Color change is very distinct

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   Answer

   Reagent: Sodium nitroprusside. Observation: A violet/purple color appears due to the formation of Sodium thionitroprusside $\text{Na}_4[\text{Fe(CN)}_5\text{NOS}]$.