Chemistry MCQs
Topic Notes: Chemistry
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
41
Which chemical compound serves as the primary active component in vinegar?
Answer:
Acetic acid
Vinegar is essentially a dilute solution of acetic acid (ethanoic acid) produced through the fermentation of ethanol by acetic acid bacteria. It typically contains 4-8% acetic acid by volume, which gives vinegar its characteristic sour taste and pungent smell.
42
Which of the following compounds is classified as a tribasic acid?
Answer:
Citric acid
A tribasic acid is an acid that has three replaceable hydrogen atoms per molecule. Citric acid (C6H8O7) contains three carboxylic acid groups (-COOH), each capable of donating a proton in an aqueous solution, making it a classic example of a tribasic organic acid.
43
Which organic acid is predominantly found in oranges?
Answer:
Citric acid
Citric acid is a weak organic acid that is naturally abundant in citrus fruits, including oranges, lemons, and limes. It is responsible for the characteristic tart and sour taste of these fruits and is widely used in the food industry as a natural preservative and flavoring agent.
44
Which of the following chemical substances is widely recognized for having a strong, characteristic fruity fragrance?
Answer:
Methanoic acid
Esters are generally known for their pleasant, fruity odors. Ethyl acetate is a classic example of an ester used in perfumes and food flavorings. However, the provided answer key identifies methanoic acid (formic acid) as the correct choice. Methanoic acid actually has a pungent, irritating odor. The source answer is preserved despite the factual discrepancy regarding the odor profile.
45
Which of the following compounds does not contain a carboxylic acid (-COOH) functional group?
Answer:
Ascorbic acid
Citric, lactic, and tartaric acids are all organic acids containing the carboxyl group. Ascorbic acid (Vitamin C), despite its name, is a lactone (cyclic ester) and an enediol, not a carboxylic acid. It lacks the -COOH functional group in its structure.
46
Which chemical test is commonly used to identify the presence of a carboxylic acid group?
Answer:
NaHCO3
Carboxylic acids react with sodium bicarbonate (NaHCO3) to produce carbon dioxide gas, which causes effervescence. This is a characteristic chemical test used to distinguish carboxylic acids from other organic compounds like alcohols or aldehydes, which do not typically react with bicarbonate to release CO2 gas.
47
What is the characteristic odor associated with most esters?
Answer:
fruit like
Esters are organic compounds formed by the reaction of an acid with an alcohol. They are widely known in chemistry for their pleasant, sweet, and often fruity aromas. Because of these properties, many synthetic esters are used extensively in the food and perfume industries to mimic natural fruit scents like banana, pineapple, or apple.
48
Match the organic acids in List-I with their corresponding natural sources in List-II.
Answer:
a-2, b-1, c-3, d-4
Formic acid is found in red ants (a-2). Lactic acid is found in milk (b-1). Tartaric acid is found in tamarind (c-3). Glutamic acid is found in wheat (d-4). Matching these pairs correctly results in the sequence a-2, b-1, c-3, d-4, which corresponds to option A.
49
What is the primary chemical component found in vinegar?
Answer:
acetic acid
Vinegar is an aqueous solution primarily composed of acetic acid (ethanoic acid), typically at a concentration of 5% to 8% by volume. It is produced through the fermentation of ethanol by acetic acid bacteria. The other acids listed are either strong mineral acids or toxic organic acids not found in food-grade vinegar.
50
Which class of organic compounds is characterized by the general structure R-COOH, where R represents an alkyl, alkenyl, aryl, or other group?
Answer:
Carboxylic acid
The general formula R-COOH defines a carboxylic acid. The functional group -COOH consists of a carbonyl group (C=O) attached to a hydroxyl group (-OH). This specific arrangement is the defining feature of carboxylic acids, distinguishing them from aldehydes (R-CHO), ketones (R-CO-R'), and esters (R-COOR').