Chapter Five · Organic chemistry · Chemistry. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 40 questions on this lesson, each with an explanation.
Ethanoic acid is added to solid sodium carbonate. The gas evolved:
Correct answer: (A) Turns limewater milky
Explanation: Carboxylic acids react with carbonates to release carbon dioxide, which turns limewater milky.
Which compound is classified as a dicarboxylic (dibasic) acid?
Correct answer: (B) Phthalic acid
Explanation: Phthalic acid under the category of dicarboxylic (dibasic) aromatic acids.
What is pure 100% acetic acid called when it freezes at 16°C forming solid substances like ice?
Correct answer: (B) Glacial acetic acid
Explanation: Acetic acid CH3COOH (pure 100%)... It freezes at 16°C forming solid substances as ice.Therefore it is called glacial acetic acid.
Which of the following arranges the substances in order of decreasing acidic strength?
Correct answer: (B) ethanoic acid > phenol > water > ethanol
Explanation: Acidity decreases in the order carboxylic acid (ethanoic) > phenol > water > alcohol (ethanol).
Why do carboxylic acids have higher boiling points than alcohols of similar molecular mass?
Correct answer: (D) Each acid molecule is linked to another by two hydrogen bonds.
Explanation: The textbook states that carboxylic acids have higher boiling points because each acid molecule is linked to another by two hydrogen bonds, forming association.
The carboxyl group (-COOH) of a carboxylic acid can be regarded as a combination of which two groups on the same carbon atom?
Correct answer: (B) A carbonyl group and a hydroxyl group
Explanation: The carboxyl group consists of a carbonyl group (C=O) and a hydroxyl group (-OH) attached to the same carbon atom.
Which of the following compounds contains a carbonyl group bound directly to a sodium oxygen ionic bond (salt)?
Correct answer: (B) CH₃-C(=O)-O-Na⁺
Explanation: Structure (c) is CH₃-C(=O)-O⁻Na⁺, which is sodium acetate.
Which of the following pairs correctly links a complex chemical with its chemical name/category?
Correct answer: (B) (COO)2Ca - Calcium salt of a carboxylic acid
Explanation: (COO)2Ca is calcium oxalate, representing a salt of a carboxylic acid as deduced from the context of organic acid derivatives.
Which chemical transformation represents the exact reverse (opposite) of reducing acetic acid with hydrogen in the presence of copper chromate at 200°C?
Correct answer: (A) Oxidation of ethanol to acetic acid
Explanation: Carboxylic acids are reduced by hydrogen in the presence of CuCrO4 at 200°C to form ethanol, and notes that 'This reaction is opposite to that of oxidation of alcohols to acids.'.
Based on the descriptions of organic acids in our life, what is the precise chemical justification for using sodium benzoate (at 0.1%) and citric acid in foods?
Correct answer: (A) Sodium benzoate prevents the growth of fungi on foods, while citric acid prevents the growth of bacteria in foods because it decreases their pH.
Explanation: Sodium benzoate 0.1% is used as foods preservating substance, because it prevents the growth of fungi on foods' and regarding citric acid: 'It prevents the growth of bacteria in foods because it decreases their (pH).
The first 10 questions in every subject are free, each with an explanation.