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Which of the following is used as an olfactory indicator to detect the acidic or basic nature of a substance?
Phenolphthalein
Methyl orange
Vanilla essence
Litmus paper
Vanilla essence
Olfactory indicators are substances whose smell changes in acidic or basic media. Vanilla essence is a classic olfactory indicator because its characteristic pleasant smell is retained in acidic solutions but completely destroyed or neutralized in basic solutions.
Olfactory indicators are substances whose smell changes in acidic or basic media. Vanilla essence is a classic olfactory indicator because its characteristic pleasant smell is retained in acidic solutions but completely destroyed or neutralized in basic solutions.
Think of it like a perfume that smells wonderful normally but loses its scent when sprayed on a specific fabric; here, the 'fabric' is the base, and the 'scent' is the indicator.
O-V-O: Olfactory, Vanilla, Onion (as these are common examples).
C8тАЛH8тАЛO3тАЛ тАФ The chemical formula for Vanillin
The principle relies on the chemical reaction between the active components of the indicator and the ions present. Vanilla essence contains vanillin (C8тАЛH8тАЛO3тАЛ), an aromatic aldehyde. In the presence of a strong base like NaOH, the aldehyde group undergoes chemical changes, leading to the loss of its distinct aromatic volatile character, thus rendering it odorless.
Olfactory indicators are useful for visually impaired students for qualitative analysis.
Common olfactory indicators include onion, vanilla extract, and clove oil.
Onion juice loses its characteristic smell in a basic solution but retains it in an acidic solution.
Useful for students with visual impairment.
Requires no complex equipment, just the sense of smell.
Cannot provide exact pH values.
Subjective, as different people have different olfactory sensitivity.
Quick field tests for identifying alkaline contaminants.
Educational demonstrations in chemistry labs.
Phenolphthalein is a synthetic acid-base indicator that is colorless in acidic and pink in basic solutions.
Methyl orange is a synthetic indicator that turns red in acidic and yellow in basic solutions.
Litmus is a natural dye derived from lichens, turning red in acid and blue in base.
C is correct тАФ Vanilla essence acts as an olfactory indicator because its distinct scent disappears in the presence of a basic substance while remaining stable in an acidic environment.
Remember that synthetic indicators like Phenolphthalein and Methyl orange change color, whereas olfactory indicators change smell. Keep these categories distinct for exam questions.