Ethanol Questions

Ethanol is a common industrial chemical that is used as a solvent in the production of other organic compounds, and as a fuel additive. Many alcoholic beverages, such as beer, wine, and distilled spirits, contain ethanol as an intoxicating element.

Definition: It is a simple alcohol with the chemical formula C₂H₆O. It’s a colourless, volatile, flammable liquid with a wine-like odour and a pungent flavour.

Ethanol Chemistry Questions with Solutions

Q-1: The general formula for alcohol is CnH2n+1 OH. What is the value of ‘n’ for ethanol?

  1. 1
  2. 3
  3. 2
  4. 5

Answer: c) 2

Explanation: ‘n’ signifies the number of carbon atoms present in the compound. The prefix “eth” stands for the number 2. This implies that ‘n’ is equal to 2 for ethanol.

Q-2: When ethanol reacts with active metals, what is formed?

  1. Metal oxide
  2. Metal Alkoxide
  3. Metal hydroxide
  4. Metal carbonate

Answer: b) Metal Alkoxide

Explanation: The following is the reaction between metal sodium and ethanol:

2CH3CH2OH + 2Na → 2CH3CH2O–Na+ + H2

The ultimate product of the process is hydrogen gas and sodium ethoxide (metal alkoxide).

Q-3: In ethanol, which of the following functional group is present?

  1. -O-
  2. -OH
  3. -COOH
  4. -CHO

Answer: b) R-OH

Explanation: A functional group is a collection of atoms or bonds that characterise the chemical properties of the hydrocarbon to which they are linked.

The following is a list of some common functional groups and their representations:

Functional group Name Representation
Aldehyde -CHO
Alcohol -OH
Carboxylic acid -COOH
Ester -COO-
Ether -O-
Amine -NH2
Ketone -CO-

Because ethanol belongs to the alcohol class, it has the functional group -OH.

Q-4: What causes ethanol to be so water-soluble?

Answer: Alcohols can establish hydrogen bonds with water molecules as shown, which explains their solubility in water. As the size of the alkyl (hydrophobic) group gets larger, solubility decreases.

Hydrogen bonding

Q-5: For the burning of ethanol, the balanced chemical equation is

C2H5OH(l) + 3O2→ 2CO2(g) + 3H2O(g)

How many moles of oxygen react with 6 moles of ethanol?

Answer:

According to the given equation,

Number of moles of oxygen required by 1 mol of ethanol = 3 moles

Thus, Number of moles of oxygen required by 6 moles of ethanol = ( 3×6) moles = 18 moles

Q-6: The most stable conformer of 2-fluoro ethanol is

  1. Partially eclipsed
  2. Fully eclipsed
  3. Gauche
  4. Anti

Answer: c) Gauche

Explanation: Different conformers of 2-fluoro ethanol are shown below: Conformers of 2-Fluoro ethanol

Gauche form is more stable due to the formation of H-bonding as shown.

Q-7: An isomer of ethanol is

  1. Acetone
  2. Methanol
  3. Diethyl ether
  4. 1-methoxymethane

Answer: d) 1-methoxymethane

Explanation: Isomers are molecules that have the same molecular formula but distinct atomic configurations.

Below table shows the structure of compounds given with their molecular formula:

Chemical Compound Structural formula Molecular formula
Acetone CH3COCH3 C3H6O
Methanol CH3OH CH4O
Diethyl ether CH3CH2OCH2CH3 C4H10O
1-methoxymethane CH3OCH3 C2H6O

Because the molecular formula of ethanol is C2H6O, its isomer is 1-methoxy methane.

Q-8: In order to get ethanol from formaldehyde, which grignard reagent is used?

  1. Ethyl magnesium bromide
  2. Methyl magnesium bromide
  3. Ethyl magnesium chloride
  4. Propyl magnesium bromide

Answer: b) Methyl magnesium bromide

Explanation: Alcohols are produced by the reaction of Grignard reagents with aldehydes and ketones .The first step of the reaction is the nucleophilic addition of Grignard reagent to the carbonyl group to form an adduct. Hydrolysis of the adduct yields an alcohol.

The reaction between methyl magnesium bromide and formaldehyde(HCHO) is shown below:

HCHO + CH3MgBr → CH3CH2OMgBr

\(\begin{array}{l}\overset{H_{2}O}{\rightarrow}\end{array} \)
CH3CH2OH + Mg(OH)Br

Note: Grignard reagents are used to increase the carbon atoms in the hydrocarbon chain. Use that grignard reagent which consists of only one C-atom.

Q-9: Ethanol is denatured in several ways. Denaturing alcohol serves what purpose?

Answer: Denatured alcohol is ethanol that has been treated with additives to make it toxic, bad-tasting, foul-smelling, or unpleasant in order to discourage recreational use.

Its primary goal is to render it unfit for human consumption.

Q-10: Methylated spirits is a mixture of

  1. 98% ethanol +2% methanol
  2. 95% ethanol + 5% methanol
  3. 95% methanol + 5% methanol
  4. 98% methanol +2% ethanol

Answer: b) 95% ethanol + 5% methanol

Q-11: Which of the following microbe is involved in the alcoholic fermentation?

  1. Clostridium butylicum , a bacterium
  2. Lactobacillus , a bacterium
  3. Saccharomyces cerevisiae , a fungus
  4. Aspergillus niger , a fungus

Answer: c) Saccharomyces cerevisiae,a fungus

Explanation: The anaerobic conversion of fructose and glucose (sugars) to ethanol and carbon dioxide is known as alcoholic fermentation. Yeasts ,a few bacteria (Zymomonas mobilis) and fungus (Saccharomyces cerevisiae) are involved in the process.

Q-12: After fermentation, ethanol is recovered by

  1. Centrifugation
  2. Distillation
  3. Separating funnel
  4. Filtration

Answer: b) Distillation

Q-13: How is ethanol prepared from alcoholic fermentation? Give the diagrammatic representation.

Answer: The process of alcoholic fermentation uses two main processes: glycolysis and fermentation.

  1. Glycolysis is the breakdown of glucose into two pyruvate molecules.
  2. Fermentation converts pyruvate molecules into two carbon dioxide molecules and two ethanol molecules.Saccharomyces cerevisiae primarily directs the pyruvate for the production of ethanol to regenerate NAD+ consumed by the process of glycolysis.

Alcoholic fermentation

Q-14: How can you convert But-2-ene to ethanol?

Answer: The conversion can be takes place as shown below:

\(\begin{array}{l}CH_{3}-CH=CH-CH_{3} \xrightarrow[Zn/H_{2}O]{O_{3}} 2CH_{3}CHO\end{array} \)
\(\begin{array}{l}CH_{3}CHO \overset{LiAlH_{4}}{\rightarrow}CH_{3}CH_{2}OH\end{array} \)

Q-15: Ethanol is

  1. Primary alcohol
  2. Secondary alcohol
  3. Tertiary alcohol
  4. Quaternary alcohol

Answer: a) Primary alcohol

Practise Questions on Ethanol

Q-1: The temperature required for acid catalysed dehydration of ethanol is

  1. 413 K
  2. 443 K
  3. 423 K
  4. 433 K

Q-2: Which option accurately predicts the vapour pressure difference between dimethyl ether and ethanol at room temperature?

  1. Dimethyl ether will have lower vapour pressure because it does not form a H-bond.
  2. Dimethyl ether will have higher vapour pressure because it does not form H-bond
  3. Dimethyl ether will have lower vapour pressure because it is larger and has more intermolecular forces.
  4. Dimethyl ether will have the same lower vapour pressure because it has the same intermolecular forces as ethanol.

Q-3: What is octane number? Is ethanol’s octane number higher than gasoline?

Q-4: What are the various purposes of ethanol?

Q-5: The other name of ethyl alcohol is

  1. Wheat alcohol
  2. Flour alcohol
  3. Grain alcohol
  4. None of the above

Click the PDF to check the answers for Practice Questions.
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