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Carbon and its Compounds - SOME IMPORT ANT C ARBON COMPOUNDS – ETHANOL

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Ethanol is a liquid at room temperature with the chemical formula C2H5OHC_2H_5OH (also written as CH3CH2OHCH_3CH_2OH). It is the second member of the homologous series of alcohols.

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Physical Properties: It is a colorless liquid with a pleasant smell and a burning taste. It is soluble in water in all proportions and is a good solvent used in medicines like tincture of iodine, cough syrups, and tonics.

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Chemical Properties - Reaction with Sodium: Ethanol reacts with sodium metal to evolve hydrogen gas (H2H_2) and form sodium ethoxide (C2H5ONaC_2H_5ONa).

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Chemical Properties - Dehydration: Heating ethanol at 443 K443 \text{ K} with excess concentrated sulphuric acid (H2SO4H_2SO_4) results in the dehydration of ethanol to give ethene (C2H4C_2H_4).

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In the dehydration reaction, concentrated H2SO4H_2SO_4 acts as a dehydrating agent because it removes a water molecule from ethanol.

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Oxidation: Ethanol can be oxidized to ethanoic acid (CH3COOHCH_3COOH) using oxidizing agents like alkaline potassium permanganate (alkaline KMnO4KMnO_4) or acidified potassium dichromate (acidified K2Cr2O7K_2Cr_2O_7).

📐Formulae

C2H5OH (Molecular Formula of Ethanol)C_2H_5OH \text{ (Molecular Formula of Ethanol)}

2C2H5OH+2Na→2C2H5ONa+H2↑2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2 \uparrow

CH3−CH2OH→443 Kconc. H2SO4CH2=CH2+H2OCH_3-CH_2OH \xrightarrow[443 \text{ K}]{\text{conc. } H_2SO_4} CH_2=CH_2 + H_2O

CH3CH2OH→HeatAlkaline KMnO4CH3COOHCH_3CH_2OH \xrightarrow[\text{Heat}]{\text{Alkaline } KMnO_4} CH_3COOH

💡Examples

Problem 1:

A student takes 2 mL2 \text{ mL} of ethanol in a test tube and adds a small piece of sodium metal to it. Name the gas evolved and write the chemical equation for the reaction.

Solution:

The gas evolved is Hydrogen (H2H_2). The chemical equation is: 2C2H5OH+2Na→2C2H5ONa+H2↑2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2 \uparrow

Explanation:

When alcohols like ethanol react with active metals like sodium, the acidic hydrogen of the hydroxyl group is replaced by the metal, releasing hydrogen gas which burns with a 'pop' sound.

Problem 2:

What happens when ethanol is heated with excess concentrated H2SO4H_2SO_4 at 443 K443 \text{ K}? Write the role of H2SO4H_2SO_4 in this reaction.

Solution:

Ethanol undergoes dehydration to form ethene (C2H4C_2H_4). CH3CH2OH→443 Kconc. H2SO4CH2=CH2+H2OCH_3CH_2OH \xrightarrow[443 \text{ K}]{\text{conc. } H_2SO_4} CH_2=CH_2 + H_2O The concentrated H2SO4H_2SO_4 acts as a dehydrating agent.

Explanation:

The acid facilitates the removal of a water molecule (one −OH-OH group and one hydrogen atom from adjacent carbon atoms) to create a double bond between the carbon atoms.

Problem 3:

How can you distinguish between ethanol and ethanoic acid on the basis of their reaction with carbonates?

Solution:

Ethanol does not react with sodium carbonate (Na2CO3Na_2CO_3) or sodium hydrogen carbonate (NaHCO3NaHCO_3). However, ethanoic acid reacts with them to produce brisk effervescence due to the evolution of carbon dioxide (CO2CO_2) gas.

Explanation:

Carboxylic acids are acidic enough to decompose carbonates and bicarbonates into salt, water, and CO2CO_2, whereas simple alcohols like ethanol are not acidic enough to perform this reaction.