Alkanols: Classification, Reactions, Industrial Preparation, and Fermentation Alıştırma Soruları — JAMB UTME

Soru 1Soru →

A $45.0\text{ g}$ sample of impure glucose containing $80.0\%$ pure glucose ( $C_6H_{12}O_6$ ) by mass undergoes complete fermentation in the presence of zymase enzyme at suitable conditions. What is the volume of carbon dioxide gas, in $\text{dm}^3$ , released at standard temperature and pressure (STP)?

(Relative atomic masses: $C = 12.0$ , $H = 1.0$ , $O = 16.0$ ; Molar volume of gas at STP $= 22.4\text{ dm}^3\text{mol}^{-1}$ )

Cevabı ve açıklamayı göster

Cevap: 8.96

Cevap

The volume of carbon dioxide gas released at STP is

8.96\text{ dm}^3

.

The complete fermentation of glucose is represented by the equation

C_6H_{12}O_6 \xrightarrow{\text{zymase}} 2C_2H_5OH + 2CO_2

. Taking into account the

80.0\%

purity, the mass of active glucose is

0.800 \times 45.0\text{ g} = 36.0\text{ g}

, which corresponds to

\frac{36.0}{180.0} = 0.200\text{ mol}

. Because

1\text{ mol}

of glucose yields

2\text{ mol}

of

CO_2

,

0.400\text{ mol}

of

CO_2

is produced. At STP,

0.400\text{ mol} \times 22.4\text{ dm}^3\text{mol}^{-1} = 8.96\text{ dm}^3

.

Adım Adım Çözüm

1

Determine the mass of pure glucose in the impure sample

36.0 g of pure glucose

Only the active pure glucose undergoes fermentation.

2

Calculate the molar mass of glucose (

C_6H_{12}O_6

)

180.0 g/mol

Needed to convert mass of reactant into molar amount.

3

Calculate the number of moles of glucose fermented

0.200 mol of glucose

Moles = Mass / Molar mass.

4

Determine moles of CO2 evolved using reaction stoichiometry

0.400 mol of CO2

Fermentation of 1 mole of hexose sugar produces 2 moles of ethanol and 2 moles of carbon dioxide.

5

Calculate the volume of CO2 gas at STP

8.96 dm^3

Volume = Moles × Molar volume at STP.

Anahtar Kavram

Fermentation Stoichiometry and Molar Yield of Alkanols

Soru 2Soru →

An organic compound $X$ with the molecular formula $\text{C}_4\text{H}_{10}\text{O}$ resists oxidation when treated with acidified potassium dichromate(VI) ( $\text{K}_2\text{Cr}_2\text{O}_7/\text{H}^+$ ). When compound $X$ is heated with concentrated tetraoxosulfate(VI) acid ( $\text{H}_2\text{SO}_4$ ) at $170^\circ\text{C}$ , it undergoes dehydration to produce a major organic product $Y$ . What is the IUPAC name of compound $Y$ ?

2-methylpropanal

But-2-ene

2-methylpropene

But-1-ene

Cevabı ve açıklamayı göster

Cevap: 2-methylpropene

Cevap

2-methylpropene

The compound resisting oxidation must be a tertiary alkanol because the hydroxyl-bearing carbon lacks an alpha-hydrogen atom. The only tertiary alkanol with formula

\text{C}_4\text{H}_{10}\text{O}

is 2-methylpropan-2-ol. Subjecting 2-methylpropan-2-ol to intra-molecular dehydration using concentrated tetraoxosulfate(VI) acid at

170^\circ\text{C}

removes water to form 2-methylpropene as the major alkene product.

Adım Adım Çözüm

1

Determine the structural class of compound X from its resistance to oxidation.

Compound X is a tertiary alkanol.

Primary and secondary alkanols are readily oxidized by acidified potassium dichromate(VI), whereas tertiary alkanols resist mild oxidation because the carbon atom bonded to the hydroxyl group (

-OH

) carries no hydrogen atoms.

2

Identify the specific isomer of formula

\text{C}_4\text{H}_{10}\text{O}

corresponding to a tertiary alkanol.

Compound X is 2-methylpropan-2-ol,

(\text{CH}_3)_3\text{C-OH}

.

Among the four structural isomers of

\text{C}_4\text{H}_{10}\text{O}

alkanols, only 2-methylpropan-2-ol is tertiary.

3

Determine the elimination product when 2-methylpropan-2-ol undergoes acid-catalyzed dehydration.

Dehydration yields 2-methylpropene,

(\text{CH}_3)_2\text{C=CH}_2

.

Heating with concentrated

\text{H}_2\text{SO}_4

at

170^\circ\text{C}

removes a molecule of water (the

-OH

group and a hydrogen atom from an adjacent methyl group), forming an alkene.

Anahtar Kavram

Classification of alkanols based on oxidation behavior and acid-catalyzed dehydration to alkenes

Tahmini Süre:2m 0s

Soru 3Soru →

During the industrial conversion of starch into ethanol through fermentation, starch is hydrolyzed to maltose, maltose is converted to glucose, and glucose is decomposed into ethanol and carbon(IV) oxide. Which of the following represents the correct sequential order of enzymes catalyzed in this process?

Diastase

\rightarrow

Maltase

\rightarrow

Zymase

\rightarrow

Diastase

\rightarrow

Maltase

\rightarrow

Diastase

\rightarrow

Zymase

Diastase

\rightarrow

Zymase

\rightarrow

Maltase

Cevabı ve açıklamayı göster

Cevap: Diastase $\rightarrow$ Maltase $\rightarrow$ Zymase

Cevap

The correct sequence of enzymes in the fermentation of starch to ethanol is diastase, followed by maltase, and finally zymase.

The production of ethanol from starch involves three sequential enzyme reactions: diastase hydrolyzes starch to maltose, maltase hydrolyzes maltose into glucose units, and zymase ferments glucose to yield ethanol and carbon(IV) oxide gas.

Adım Adım Çözüm

1

Identify the enzyme that hydrolyzes starch to maltose

Starch is converted to maltose by the enzyme diastase present in malt.

Complex polysaccharides like starch require diastase for initial breakdown into disaccharides.

2

Identify the enzyme that converts maltose into glucose

Maltose is converted into glucose by the enzyme maltase.

Maltase specifically breaks down the disaccharide maltose into monosaccharide glucose units.

3

Identify the enzyme that ferments glucose into ethanol

Glucose is decomposed into ethanol and carbon(IV) oxide by the enzyme zymase.

Zymase secreted by yeast catalyzes the final fermentation step converting monosaccharides into alcohol.

Anahtar Kavram

Sequential enzyme-catalyzed reactions in starch fermentation to produce ethanol

Tahmini Süre:1m 0s

Soru 4Soru →

When an unknown alkanol is warmed with acidified potassium heptaoxodichromate(VI) ( $K_2Cr_2O_7$ ) solution, the orange solution turns green and an alkanone is produced. Which of the following compounds undergoes this reaction?

Propan-2-ol

Propan-1-ol

2-Methylpropan-2-ol

Ethanol

Cevabı ve açıklamayı göster

Cevap: Propan-2-ol

Cevap

Propan-2-ol is a secondary alkanol that undergoes oxidation to form an alkanone (propanone), changing the color of acidified potassium heptaoxodichromate(VI) from orange to green.

Propan-2-ol is a secondary alkanol (

CH_3-CH(OH)-CH_3

). Upon oxidation with acidified

K_2Cr_2O_7

, the orange dichromate(VI) ions (

Cr_2O_7^{2-}

) are reduced to green chromium(III) ions (

Cr^{3+}

), and the secondary alcohol is converted into propanone (

CH_3COCH_3

), which belongs to the alkanone family.

Adım Adım Çözüm

1

Classify the given alkanols by structural type (primary, secondary, or tertiary).

Propan-1-ol and ethanol are primary alkanols; propan-2-ol is a secondary alkanol; 2-methylpropan-2-ol is a tertiary alkanol.

The reaction outcome of alkanol oxidation depends strictly on the classification of the hydroxyl-bearing carbon atom.

2

Determine the oxidation product for each classification type.

Primary alkanols oxidize to alkanals (and further to alkanoic acids); secondary alkanols oxidize to alkanones; tertiary alkanols resist mild oxidation.

Secondary alkanols have one hydrogen atom on the hydroxyl carbon, which allows dehydrogenation to form a carbonyl double bond (

C=O

) bounded by two alkyl groups (ketone/alkanone).

3

Match the specified product (alkanone) to the correct compound.

Propan-2-ol oxidizes to propanone (

CH_3COCH_3

), which is an alkanone.

Only the secondary alkanol propan-2-ol yields an alkanone.

Anahtar Kavram

Oxidation of Alkanols (Primary, Secondary, and Tertiary Classification)

Tahmini Süre:1m 0s

Soru 5Soru →

Match each class of alkanol listed on the left with its characteristic oxidation behavior on the right when reacted with acidified potassium heptaoxodichromate(VI) solution.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Cevabı ve açıklamayı göster

Cevap

Primary alkanols pair with oxidation to an alkanal and then an alkanoic acid; secondary alkanols pair with oxidation to an alkanone; tertiary alkanols pair with resistance to oxidation under mild conditions.

Primary alkanols possess two alpha-hydrogens and oxidize in two steps to form alkanals and then alkanoic acids. Secondary alkanols possess one alpha-hydrogen and oxidize to form alkanones. Tertiary alkanols lack alpha-hydrogens entirely, rendering them resistant to oxidation under mild conditions.

Adım Adım Çözüm

1

Examine the structural environment of primary alkanols (

R-CH_2OH

)

Primary alkanols have two

\alpha

-hydrogen atoms attached to the carbon holding the

-OH

group, permitting two sequential oxidation steps.

Oxidation requires the removal of hydrogen from the hydroxyl-bearing carbon atom.

2

Examine the structural environment of secondary alkanols (

R_2CHOH

)

Secondary alkanols have only one

\alpha

-hydrogen atom, yielding an alkanone (

R_2C=O

).

Alkanones resist further oxidation under mild conditions because no additional

\alpha

-hydrogens are available.

3

Examine the structural environment of tertiary alkanols (

R_3COH

)

Tertiary alkanols possess zero

\alpha

-hydrogen atoms on the hydroxyl-bearing carbon atom.

Without an

\alpha

-hydrogen, oxidation cannot proceed without breaking carbon-carbon bonds.

Anahtar Kavram

Classification and oxidation products of alkanols

Soru 6Soru →

Match each chemical transformation involving alkanols listed on the left with the appropriate reagent, enzyme, or catalyst required on the right.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Cevabı ve açıklamayı göster

Cevap

Glucose is fermented to ethanol using the enzyme zymase; dehydration of ethanol to ethene uses excess concentrated

\text{H}_2\text{SO}_4

at

170^\circ\text{C}

; ethanol is oxidized to ethanoic acid using acidified

\text{K}_2\text{Cr}_2\text{O}_7

under reflux; and industrial synthesis of ethanol from ethene uses steam with a phosphoric acid (

\text{H}_3\text{PO}_4

) catalyst at high temperature and pressure.

Each chemical process matches its unique catalyst or reaction conditions: zymase catalyzes glucose fermentation to ethanol, excess concentrated

\text{H}_2\text{SO}_4

at

170^\circ\text{C}

dehydrates ethanol to ethene, acidified

\text{K}_2\text{Cr}_2\text{O}_7

under reflux oxidizes ethanol to ethanoic acid, and phosphoric acid (

\text{H}_3\text{PO}_4

) on silica catalyzes the industrial hydration of ethene to ethanol.

Adım Adım Çözüm

1

Identify the biological catalyst for sugar fermentation

Fermentation of glucose (

\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2

) is catalyzed specifically by the enzyme zymase.

Yeast produces zymase, which converts simple hexose sugars directly into ethanol.

2

Identify the reagent and temperature for elimination/dehydration

Heating ethanol with excess concentrated

\text{H}_2\text{SO}_4

at

170^\circ\text{C}

yields ethene via removal of a water molecule.

Concentrated tetraoxosulfate(VI) acid acts as a dehydrating agent; high temperature (

170^\circ\text{C}

) favors ethene formation over ethoxyethane formation.

3

Identify the oxidizing conditions for full alkanol oxidation

Primary alkanols undergo two-stage oxidation: first to an alkanal, then under reflux with acidified

\text{K}_2\text{Cr}_2\text{O}_7

to an alkanoic acid.

Acidified potassium heptaoxodichromate(VI) is a strong oxidizing agent capable of carrying the oxidation of ethanol fully to ethanoic acid.

4

Identify the industrial catalytic addition reaction conditions

Direct hydration of ethene (

\text{C}_2\text{H}_4 + \text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_5\text{OH}

) uses a phosphoric acid catalyst.

The reversible addition of steam across the double bond of ethene requires a solid phosphoric acid catalyst at

300^\circ\text{C}

and high pressure.

Anahtar Kavram

Reagents, enzymes, and conditions for alkanol preparation and reactions

Alkanols: Classification, Reactions, Industrial Preparation, and Fermentation

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