BharatNotes Indicator
nounUsage in a UPSC answer
Per capita income alone is a misleading indicator of well-being, for it masks the stark inequalities that composite measures such as the Human Development Index are designed to expose.
Synonyms
Antonyms
Word Family
indicate (v), indication (n), indicative (adj), indicatively (adv), indicators (n pl)
Root
Late Latin indicātor = one who points out; Latin indicāre = to make known; in- = towards + dicāre = to proclaim
Etymology
From Late Latin indicātor (one who points out), from Latin indicāre (to make known, point out), from in- (towards) + dicāre (to proclaim); first recorded in English in the 1660s.
Memory Hook
In-DICA-tor: think of the Latin dicare, 'to proclaim' — an indicator is a finger that 'proclaims' and points out (in-dicates) where things stand.
How This Word Works in UPSC Writing
A substance that changes colour over a characteristic pH range, signalling the acidity of a solution or the end point of a titration. The point that turns a definition into understanding is that indicators are themselves weak acids or bases whose undissociated and dissociated forms differ in colour, so the colour reports the ratio of the two, which is why each indicator changes over a range rather than at a single value. It follows that the indicator must be matched to the titration: phenolphthalein, colourless in acid and pink in base with a range around 8.3 to 10.0, suits a strong base against a weak acid, while methyl orange, red to yellow around 3.1 to 4.4, suits a strong acid against a weak base. Natural indicators such as litmus from lichens, turmeric and red cabbage extract make the same chemistry demonstrable without a laboratory.
Don’t Confuse It With
An indicator changes colour over a pH range, while universal indicator is a mixture giving a graded series of colours across the whole scale rather than a single sharp change. An olfactory indicator such as onion or vanilla signals by change in smell rather than colour, which allows the concept to be taught to students who cannot see colour. The end point is what the indicator marks, while the equivalence point is the true stoichiometric completion. Note the general statistical sense of indicator, meaning a measurable proxy for something harder to observe, which is the sense used in the sentence above.
Hindi Meaning
सूचक (sūchak); सार्वत्रिक सूचक for universal indicator.
Common Questions
- What is an indicator in chemistry?
- A substance that changes colour over a specific pH range, used to show whether a solution is acidic or basic and to mark the end point of a titration.
- Why do different titrations need different indicators?
- Because each indicator changes colour over its own pH range, and it must be chosen so that its range falls close to the pH at the equivalence point of that particular titration.
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