Practical Organic Chemistry

Let's examine each statement one by one to choose the most appropriate answer : Statement (I) : Potassium hydrogen phthalate is a primary standard for standardisation of sodium hydroxide solution.

This statement is correct.

Potassium hydrogen phthalate (often abbreviated as KHP, with the chemical formula

) is commonly used as a primary standard in titrations because it is pure, stable, non-hygroscopic, and has a high molar mass.

It reacts with sodium hydroxide (NaOH) in a stoichiometric reaction, where one mole of KHP reacts with one mole of NaOH.

The equation for the reaction is as follows :

Statement (II) : In this titration phenolphthalein can be used as indicator.

This statement is also correct.

Phenolphthalein is a suitable indicator for the titration between KHP and NaOH.

It changes color in the pH range of about 8.2 to 10, which is appropriate for the endpoint of a titration involving a weak acid (KHP) and a strong base (NaOH).

In an acidic solution, phenolphthalein is colorless, but it turns pink in a basic solution, signaling the end of the titration when slight excess NaOH is present.

Given that both statements are correct, the most appropriate answer is : Option A : Both Statement I and Statement II are correct.

Nitrogen Detection (Lassaigne's Test) Nitrogen in organic compounds is detected by converting it into sodium cyanide, which further reacts with iron(II) sulfate to form sodium hexacyanoferrate(II).

By reacting this with iron(III) ions, Prussian blue is formed: $$\begin{aligned} &\mathrm{Na}+\mathrm{C}+\mathrm{N} \rightarrow \mathrm{NaCN} \\\\ &6 \mathrm{NaCN}+\mathrm{FeSO}_4 \rightarrow \mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]+\mathrm{Na}_2 \mathrm{SO}_4 \\\\ &\mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]+\mathrm{Fe}^{3+} \rightarrow \mathrm{Fe}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]_3 \text{ (Prussian blue)} \end{aligned}$$ Sulphur Detection Sulphur can be detected using Sodium nitroprusside: $\mathrm{Na}_2\left[\mathrm{Fe}(\mathrm{CN})_5 \mathrm{NO}\right]+\mathrm{Na}_2 \mathrm{S} \rightarrow \mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_5 \mathrm{NOS}\right] \text{ [Purple]}$ Phosphorous Detection Phosphorus detection involves reaction with ammonium molybdate to form a canary yellow compound: $$\begin{aligned} &\mathrm{Na}_3 \mathrm{PO}_4+3 \mathrm{HNO}_3 \rightarrow \mathrm{H}_3 \mathrm{PO}_4+3 \mathrm{NaNO}_3 \\\\ &\mathrm{H}_3 \mathrm{PO}_4+12\left(\mathrm{NH}_4\right)_2 \mathrm{MoO}_4+21 \mathrm{HNO}_3 \rightarrow\\\\& \left(\mathrm{NH}_4\right)_3 \mathrm{PO}_4 \cdot 12 \mathrm{MoO}_3+21 \mathrm{NH}_4 \mathrm{NO}_3+12 \mathrm{H}_2 \mathrm{O} \text{ (canary yellow)} \end{aligned}$$ Halogen Detection Halogens react with silver nitrate to form specific colored precipitates: $$\begin{aligned} &\mathrm{NaCl}+\mathrm{AgNO}_3(\mathrm{aq}) \rightarrow \mathrm{AgCl}+\mathrm{NaNO}_3 \text{ (White)} \\\\ &\mathrm{NaBr}+\mathrm{AgNO}_3(\mathrm{aq}) \rightarrow \mathrm{AgBr}+\mathrm{NaNO}_3 \text{ (Pale yellow)} \\\\ &\mathrm{NaI}+\mathrm{AgNO}_3(\mathrm{aq}) \rightarrow \mathrm{AgI}+\mathrm{NaNO}_3 \text{ (Yellow)} \end{aligned}$$ Based on the above reactions, the correct matching is: Option A A-III (Nitrogen), B-I (Sulphur), C-IV (Phosphorous), D-II (Halogen).

The correct option for the purification of steam volatile water-immiscible substances is Option D, Steam distillation.

Steam distillation is a separation technique used to purify or isolate temperature-sensitive materials, such as natural aromatic compounds, that are volatile in steam at a temperature that is lower than their decomposition temperatures.

It exploits the fact that immiscible liquids can be distilled at a lower temperature than the boiling points of the individual components.

Here is how steam distillation works: Water and the other immiscible substance are placed in the distillation apparatus.

Steam is generated either within the same flask or introduced from an external source.

The hot steam helps vaporize the other substance at a temperature below its normal boiling point.

The vapors of water and the volatile substance both pass into the condenser, where they are cooled.

Upon cooling, the vapors convert back into liquid, which is then collected in a separate container.

Since the two substances are immiscible, they separate into two distinct layers, typically, with the organic compound floating on top of the water or sinking below it, depending on their densities.

The layers can then be separated using a separating funnel or other means.

Steam distillation is different from fractional distillation (Option A), which is used for the separation of a mixture into its component parts, or fractions, of compounds that are miscible and have different boiling points.

Fractional distillation often involves the use of a fractionating column, which brings more efficiency in separating substances with close boiling points.

Simple distillation (Option B) is suitable for separating a liquid from impurities or for separating liquids with significantly different boiling points (usually the difference in boiling points should be at least $25^\circ C$).

On the other hand, fractional distillation under reduced pressure (Option C) is used when a liquid has a very high boiling point or might decompose at high temperatures.

By reducing the pressure, the boiling point of the liquid is lowered and it can be distilled at a temperature much lower than its normal boiling point, thus avoiding decomposition.

Therefore, for volatile substances that are not miscible with water, steam distillation remains the ideal choice.

Steam distillation technique is applied to separate substances which are steam volatile and are immiscible with water.

Memory Based

Let's evaluate each statement to identify the incorrect ones regarding the primary standard in titrimetric analysis: (A) It should be purely available in dry form.

This statement is generally correct.

A primary standard should be pure and available in a stable, dry form to ensure accurate weight measurements.

(B) It should not undergo chemical change in air.

This statement is also correct.

A primary standard should be stable in air and not react with components of the atmosphere such as oxygen or carbon dioxide.

(C) It should be hygroscopic and should react with another chemical instantaneously and stoichiometrically.

This statement is incorrect.

A primary standard should not be hygroscopic (it should not absorb moisture from the air) because hygroscopic substances cannot maintain a constant weight.

The part about reacting stoichiometrically and instantaneously is generally correct, but being hygroscopic disqualifies a substance from being a primary standard.

(D) It should be readily soluble in water.

This statement is correct.

A primary standard should be soluble in water to ensure that it can be dissolved to make a standard solution for titration.

(E)

&

can be used as primary standard. This statement is incorrect. Both

(potassium permanganate) and

(sodium hydroxide) are not suitable as primary standards.

is unstable and can decompose, while

is hygroscopic, which makes precise weight measurements difficult.

Hence, the correct answer is: Option A (C) and (E) only

Statement A: Glycerol is purified by vacuum distillation because it decomposes at its normal boiling point.

This statement is correct.

Glycerol decomposes at its normal boiling point (290°C approximately), so vacuum distillation is used to lower the boiling point and prevent decomposition.

Statement B: Aniline can be purified by steam distillation as aniline is miscible in water.

This statement is incorrect.

Aniline is not completely miscible in water.

However, it can be purified by steam distillation due to its relatively high boiling point and water’s ability to carry it over as a vapor.

The statement as given is not entirely correct.

Statement C: Ethanol can be separated from ethanol-water mixture by azeotropic distillation because it forms an azeotrope.

This statement is correct.

Ethanol and water form a minimum boiling azeotrope, which has a constant boiling point lower than either pure component, enabling separation through azeotropic distillation.

Statement D: An organic compound is pure if the mixed melting point remains the same.

This statement is correct.

If mixing a small quantity of an unknown compound with a known compound does not change the melting point, this suggests the unknown compound is the same as the known and thus pure.

Based on the analysis, the correct statements are A, C, and D.

Option A: A, C, D only.

The sodium fusion extract of organic compound having N \& S gives blood red colour with $\mathrm{FeSO}_4$ and $\mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]$

To determine the percentage composition of nitrogen using Dumas' method, follow these calculations: Calculate the Pressure of Nitrogen Gas: $\text{Pressure of } \mathrm{N}_2 = (715 \text{ mmHg} - 15 \text{ mmHg}) = 700 \text{ mmHg}$ Calculate the Moles of Nitrogen ($\mathrm{n}_{\mathrm{N}_2}$): $\mathrm{n}_{\mathrm{N}_2} = \dfrac{\mathrm{PV}}{\mathrm{RT}}$ Where: $P = 700 \text{ mmHg}$ $V = 60 \times 10^{-3} \text{ L}$ $R = 0.0821 \text{ L atm/mol K}$ $T = 300 \text{ K}$ Plug the values into the equation: $\mathrm{n}_{\mathrm{N}_2} = \dfrac{700 \times 60 \times 10^{-3}}{760 \times 0.0821 \times 300} \approx 2.24 \times 10^{-3} \text{ mol}$ Calculate the Mass of Nitrogen Gas: $\text{Mass of } \mathrm{N}_2 = 2.24 \times 10^{-3} \text{ mol} \times 28 \text{ g/mol} = 0.06272 \text{ g}$ Determine the Percentage Composition of Nitrogen: $\% \mathrm{~N}_2 = \left(\dfrac{0.06272}{0.5}\right) \times 100 \approx 12.57\%$ Thus, the percentage composition of nitrogen in the compound is approximately 12.57%.

Organic layer in funnel are mixture of chloro benzene and aniline