Organic Chemistry – Some Basic Principles and Techniques Chapter-Wise Test 5

Correct answer Carries: 4.

Wrong Answer Carries: -1.

Which purification technique is used to separate a mixture of two miscible liquids with close boiling points?

Fractional distillation separates miscible liquids with boiling points differing by less than 25°C using a fractionating column.

Simple distillation
Sublimation
Crystallization
Fractional distillation
4

A compound with 9 \( \sigma \) bonds and 1 \( \pi \) bond has a molecular formula of \( \ce{C4H6} \). Which carbon has a bond angle closest to 109.5°?

\( \ce{CH3CH=CHCH2} \) fits \( \ce{C4H6} \) with 9 \( \sigma \) (6 C-H, 2 C-C, 1 from C=C) and 1 \( \pi \) (C=C). The first carbon (\( \ce{CH3} \)) is \( sp^3 \), with a 109.5° bond angle.

Second carbon
Third carbon
First carbon
Fourth carbon
3

Which compound with \( \ce{C4H8} \) has a degree of unsaturation of 1 and can be separated from its chain isomer by simple distillation?

\( \ce{CH2=CHCH2CH3} \) (but-1-ene) has one double bond (degree = 1). Its chain isomer, 2-methylpropene (\( \ce{CH3C(CH3)=CH2} \)), has a similar boiling point (~-6°C vs. -6.9°C), but cyclic isomers like cyclobutane (~12°C) can be separated by simple distillation due to a larger boiling point difference.

\( \ce{CH3CH=CHCH3} \)
\( \ce{CH2=CHCH2CH3} \)
\( \ce{CH3CH2C#CH} \)
\( \ce{CH3C(CH3)=CH2} \)
2

Which carbon in \( \ce{CH3CH2CH2C(=O)OCH3} \) has the greatest s-character in its hybridization?

In \( \ce{CH3CH2CH2C(=O)OCH3} \) (methyl butanoate), the carbonyl carbon (\( \ce{C=O} \)) is \( sp^2 \) hybridized (33% s-character), higher than \( sp^3 \) (25%) of other carbons.

Carbonyl carbon
Carbon in \( \ce{CH3} \) of \( \ce{CH3CH2CH2} \)
Carbon in \( \ce{CH2} \) adjacent to carbonyl
Carbon in \( \ce{OCH3} \)
1

In Kjeldahl’s method, 0.42 g of a compound produced ammonia that neutralized 15 mL of 0.2 M \( \ce{H2SO4} \). What is the percentage of nitrogen?

Moles of \( \ce{H2SO4} \) = \( 0.015 \times 0.2 = 0.003 \). Moles of \( \ce{NH3} \) = 0.006 (2H per \( \ce{H2SO4} \)). Mass of N = \( 0.006 \times 14 = 0.084 \) g. Percentage = \( \frac{0.084}{0.42} \times 100 = 20\% \).

19%
21%
22%
20%
4

In Lassaigne’s test, an organic compound gives a violet color with sodium nitroprusside and a white precipitate with silver nitrate. What elements are present?

Violet color with sodium nitroprusside indicates sulphur (\( \ce{Na2S} \)), and white precipitate with \( \ce{AgNO3} \) indicates chlorine (\( \ce{AgCl} \)).

Sulphur and chlorine
Nitrogen and sulphur
Nitrogen and chlorine
Sulphur and bromine
1

In Lassaigne’s test, the presence of bromine forms a precipitate of what color with silver nitrate?

Bromine forms \( \ce{NaBr} \) in Lassaigne’s test, which reacts with \( \ce{AgNO3} \) to form a pale yellow precipitate of \( \ce{AgBr} \).

Pale yellow
White
Yellow
Black
1

Which technique is least effective for separating a mixture of two liquids with boiling points of 110°C and 150°C, one of which is water-soluble?

Sublimation is for solids, not liquids. Simple distillation (40°C difference) or differential extraction (solubility) would work, but sublimation is irrelevant.

Sublimation
Simple distillation
Differential extraction
Fractional distillation
1

What is the hybridization of the central carbon in \( \ce{CH3CH2CH3} \)?

In \( \ce{CH3CH2CH3} \) (propane), the central carbon has four single bonds (two to C, two to H), indicating \( sp^3 \) hybridization.

\( sp \)
\( sp^3 \)
\( sp^2 \)
\( sp^3d \)
2

A hydrocarbon with a degree of unsaturation of 2 produces 4 moles of \( \ce{CO2} \) per mole upon complete combustion. What is its molecular formula?

4 carbons (from 4 \( \ce{CO2} \)). Degree of unsaturation = 2 suggests two double bonds or one triple bond. \( \ce{CH3C#CCH3} \) (but-2-yne, \( \ce{C4H6} \)) fits with 2 \( \pi \), 8 \( \sigma \), and 4 \( \ce{CO2} \).

\( \ce{C4H8} \)
\( \ce{C4H6} \)
\( \ce{C5H8} \)
\( \ce{C3H4} \)
2

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