How will you distinguish between the following pairs of compounds: (i) Chloroform and carbon tetra chloride. (ii) Benzyl alcohol and chlorobenzene.

Distinguishing between compounds can be quite fascinating, especially when they have similar structures or properties. Let’s break down the differences between the pairs you mentioned: chloroform and carbon tetrachloride, as well as benzyl alcohol and chlorobenzene.

Chloroform vs. Carbon Tetrachloride

Both chloroform (CHCl₃) and carbon tetrachloride (CCl₄) are chlorinated hydrocarbons, but they have distinct properties that can help us tell them apart.

Physical Properties

• Boiling Points: Chloroform has a boiling point of about 61.2 °C, while carbon tetrachloride boils at 76.7 °C. This difference can be observed using a simple distillation setup.
• Density: Chloroform is denser than water (density ≈ 1.48 g/cm³), whereas carbon tetrachloride is also denser than water (density ≈ 1.59 g/cm³). However, both will sink in water, but their densities can be compared using a hydrometer.

Chemical Tests

Another effective way to differentiate them is through chemical reactivity:

• Reaction with Sodium Hydroxide: Chloroform can react with sodium hydroxide to form sodium formate and other products, while carbon tetrachloride does not undergo such a reaction.
• Smell: Chloroform has a sweet, pleasant odor, while carbon tetrachloride has a more pungent, less pleasant smell. This can be a quick qualitative test, though caution is advised due to toxicity.

Benzyl Alcohol vs. Chlorobenzene

Next, let’s look at benzyl alcohol (C₇H₈O) and chlorobenzene (C₆H₅Cl). These compounds also have distinct characteristics that can be used for differentiation.

Functional Groups

• Presence of Hydroxyl Group: Benzyl alcohol contains a hydroxyl group (-OH), which makes it an alcohol. This can be confirmed through a simple test with Lucas reagent (zinc chloride in hydrochloric acid), which will show a positive reaction (cloudiness) for benzyl alcohol.
• Chlorine Atom: Chlorobenzene contains a chlorine atom directly attached to the aromatic ring. It does not have the -OH group, which is a key distinguishing feature.

Solubility and Reactivity

Another way to differentiate these compounds is through their solubility and reactivity:

• Solubility in Water: Benzyl alcohol is soluble in water due to its polar -OH group, while chlorobenzene is not soluble in water, as it is a non-polar compound.
• Reactivity with Sodium Bicarbonate: Benzyl alcohol can react with sodium bicarbonate to produce carbon dioxide, indicating its acidic nature, whereas chlorobenzene does not react in this way.

In summary, by examining physical properties, chemical reactivity, and functional groups, you can effectively distinguish between chloroform and carbon tetrachloride, as well as benzyl alcohol and chlorobenzene. Each method provides a unique insight into the nature of these compounds, enhancing your understanding of organic chemistry.