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Questions and Answers
What is the laboratory method for preparing formic acid?
Formic acid can be prepared by the hydrolysis of carbon monoxide in the presence of sodium hydroxide or by the oxidation of methanol.
Why are carboxylic acids like formic acid stronger acids than alcohols?
Carboxylic acids are stronger acids due to the resonance stabilization of their conjugate base, whereas alcohols do not have such stabilization.
Describe how butane can be synthesized using Kolbe electrolysis.
Butane can be synthesized through Kolbe electrolysis by electrolyzing an aqueous solution of sodium butyrate, leading to the coupling of two butyl radicals.
What are the reasons for formic acid acting as a reducing agent?
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Why is 100% pure acetic acid referred to as glacial acetic acid?
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Describe the reaction of formic acid with Tollens reagent.
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What is the modern method of synthesizing acetic acid from acetylene?
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Explain the reaction between monocarboxylic acids and diazomethane.
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Study Notes
Laboratory Preparation of Formic Acid
- Formic acid can be prepared in the lab by heating oxalic acid with glycerol.
- The reaction forms formic acid as the primary product, alongside water and carbon dioxide as byproducts.
- The chemical equation for the reaction is:
H2C2O4 + Glycerol → HCOOH + CO2 + H2O
Comparison of Formic Acid and Carboxylic Acids with Alcohols
- Carboxylic acids are stronger acids compared to alcohols due to the presence of a carboxyl group (-COOH).
- The carboxyl group contains a carbonyl group (C=O) and a hydroxyl group (-OH) connected to the same carbon atom.
- The electron-withdrawing effect of the carbonyl group increases the polarity of the O-H bond in the carboxyl group, making it easier for the hydrogen ion (H+) to be released.
- This results in a stronger acidic character compared to alcohols.
Kolbe Electrolysis to Synthesize Butane
- Kolbe electrolysis involves the electro-oxidation of carboxylate salts.
- It's a method used to synthesize alkanes with an even number of carbon atoms.
- The process involves the electrolysis of an aqueous solution of a carboxylate salt, which results in the formation of free radicals at the anode.
- These free radicals combine to form alkanes.
- To synthesize butane, the electrolysis of sodium propanoate is carried out:
2CH3CH2COO- → CH3CH2CH2CH3 + 2CO2 + 2e-
Reductive Properties of Formic Acid
- Formic acid acts as a reducing agent due to the presence of a formyl group (-CHO).
- This group readily releases a hydride ion (H-) in reactions, making formic acid a good reducing agent.
100% Pure Acetic Acid (Glacial Acetic Acid)
- 100% pure acetic acid is called glacial acetic acid because it freezes at 16.6°C, forming ice-like crystals.
Reductive Properties of Formic Acid - Reaction Details
- Formic acid reacts with Tollens reagent (ammoniacal silver nitrate) to form metallic silver.
- The chemical equation for this reaction is:
HCOOH + 2[Ag(NH3)2]+ + 2OH− → 2Ag + CO2 + 2H2O + 4NH3
- Formic acid reacts with concentrated sulfuric acid to produce carbon monoxide and water.
- The chemical equation for this reaction is:
HCOOH + H2SO4 → CO + H2O + H2SO4
- Formic acid reacts with Fehling's solution to form a red precipitate of cuprous oxide (Cu2O).
- The chemical equation for this reaction is:
HCOOH + 2Cu2+ + 5OH− → Cu2O + CO2 + 3H2O
- Formic acid reacts with ethyl alcohol in the presence of a catalyst like concentrated sulfuric acid to form ethyl formate.
- This reaction is an esterification reaction.
- The chemical equation for this reaction is:
HCOOH + C2H5OH → HCOOC2H5 + H2O
Modern Method for Synthesizing Acetic Acid from Acetylene
- Acetylene can be converted to acetic acid through a two-step process:
- Hydration: Acetylene reacts with water in the presence of mercuric sulfate (HgSO4) as a catalyst to form acetaldehyde.
- Oxidation: Acetaldehyde is then oxidized to acetic acid using an oxidizing agent (like oxygen in air).
- The chemical equations for these reactions are:
CH≡CH + H2O → CH3CHO (in presence of HgSO4) CH3CHO + ½O2 → CH3COOH
Reactions of Various Chemicals
- Oxalic acid reacts with glycerol to form formic acid, carbon dioxide and water.
- Dry chlorine reacts with acetic acid in sunlight to form monochloroacetic acid.
- Sodium acetate reacts with soda lime (a mixture of sodium hydroxide and calcium oxide) to form methane.
- Formic acid reacts with concentrated sulfuric acid to produce carbon monoxide and water.
- Formic acid reacts with ammoniacal silver nitrate (Tollens reagent) to form metallic silver along with carbon dioxide and water.
- Formic acid reacts with Fehling solution to form a red precipitate of cuprous oxide.
- Formic acid reacts with ethanol in the presence of a catalyst like concentrated sulfuric acid to form ethyl formate.
- Acetic acid reacts with chlorine in the presence of red phosphorus to form monochloroacetic acid.
- When Sodium formate is heated at a high temperature, it decomposes into sodium carbonate and hydrogen.
Reaction of Monocarboxylic Acids with Diazo Methane
- Monocarboxylic acids react with diazomethane to form methyl esters and nitrogen gas.
- The chemical equation for this reaction is:
RCOOH + CH2N2 → RCOOCH3 + N2
- The reaction produces diazomethane as a byproduct.
- Diazo methane is potentially explosive.
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Description
This quiz covers the laboratory preparation of formic acid, its comparison with alcohols, and the synthesis of butane through Kolbe electrolysis. Test your understanding of the chemical reactions and properties of carboxylic acids in this engaging quiz.
