Questions on Indicators
INDICATORS – MULTIPLE-CHOICE QUESTIONS
1. What is the main role of an acid–base indicator in titration?
A) To change temperature
B) To neutralize the solution
C) To detect the endpoint of a reaction
D) To dissolve the solute
E) To measure pressure
2. Which of the following indicators is colorless in acid and pink in base?
A) Methyl orange
B) Bromothymol blue
C) Phenolphthalein
D) Litmus
E) Thymol blue
3. Litmus turns red in which type of solution?
A) Basic
B) Neutral
C) Aqueous
D) Acidic
E) Saline
4. Methyl orange shows a color change from:
A) Blue to red
B) Red to yellow
C) Yellow to green
D) Colorless to pink
E) Purple to orange
5. Which indicator is most suitable for a strong acid–strong base titration?
A) Methyl orange
B) Phenolphthalein
C) Thymol blue
D) Bromophenol blue
E) Congo red
6. What is the approximate pH range for phenolphthalein?
A) 3.0 – 4.4
B) 5.2 – 6.8
C) 8.2 – 10.0
D) 6.0 – 7.5
E) 10.5 – 12.0
7. Which of the following is a universal indicator used to measure pH across a wide range?
A) Phenolphthalein
B) Litmus
C) Methyl orange
D) Universal indicator
E) Bromocresol green
8. What color does methyl orange turn in acidic solutions?
A) Red
B) Orange
C) Yellow
D) Blue
E) Green
9. What causes an indicator to change color?
A) Change in pressure
B) Change in mass
C) Change in pH
D) Change in volume
E) Change in concentration
10. Which indicator would be best for a weak acid–strong base titration?
A) Bromothymol blue
B) Methyl orange
C) Phenolphthalein
D) Litmus
E) Congo red
11. What is the typical color change of bromothymol blue from acid to base?
A) Red to blue
B) Yellow to blue
C) Orange to green
D) Blue to red
E) Purple to yellow
12. Which of the following indicators is commonly used in school laboratories for general pH testing?
A) Thymol blue
B) Phenol red
C) Universal indicator
D) Congo red
E) Alizarin yellow
13. Which indicator is not suitable for weak acid–weak base titration due to a poorly defined endpoint?
A) Methyl orange
B) Phenolphthalein
C) Litmus
D) Bromothymol blue
E) None of the above
14. What is the color of phenolphthalein in a solution with pH 3.0?
A) Red
B) Yellow
C) Blue
D) Colorless
E) Pink
15. What is the typical color of litmus in a neutral solution?
A) Red
B) Blue
C) Purple
D) Yellow
E) Colorless
16. What makes a universal indicator different from a regular acid-base indicator?
A) It has no color
B) It changes color only at pH 7
C) It works only in bases
D) It shows different colors for different pH values
E) It only works with strong acids
- Questions on Strong and Weak Acids and Acid Ionization Constant (Ka) and Base (Kb)
- Questions on Neutralization Reactions
- Questions on Titration: Experiment, Calculations, and Curves
ANSWER KEY
1. C – Indicators are used to signal the endpoint of a reaction, typically via a color change when neutralization is complete.
2. C – Phenolphthalein is colorless in acidic conditions and turns pink in basic solutions.
3. D – Litmus turns red in acidic conditions (pH below 7).
4. B – Methyl orange turns from red in acid to yellow in base.
5. B – Phenolphthalein is preferred in strong acid–strong base titrations due to its sharp color change near pH 7.
6. C – Phenolphthalein changes color in the pH range 8.2 to 10.0.
7. D – Universal indicator shows a variety of colors across a broad pH range (1–14).
8. A – Methyl orange appears red in acidic solutions.
9. C – A change in pH affects the chemical structure of the indicator, resulting in a visible color change.
10. C – Phenolphthalein is suitable for weak acid–strong base titrations because the equivalence point lies in the basic range.
11. B – Bromothymol blue changes from yellow in acid to blue in base.
12. C – Universal indicator is widely used in educational settings due to its broad range and vivid color changes.
13. E – None of the listed indicators is ideal for weak acid–weak base titrations; the pH change is too gradual for precise detection.
14. D – At pH 3.0 (acidic), phenolphthalein is colorless.
15. C – In a neutral solution (pH 7), litmus appears purple.
16. D – Unlike single-range indicators, universal indicators
Dive into the groundbreaking science of neurotransmitters—your brain’s invisible architects—in Chemical Harmony: How Neurotransmitters Shape Our Lives (2025). This meticulously researched book reveals how serotonin, dopamine, GABA, and other brain chemicals silently orchestrate every aspect of your existence, from decision-making and relationships to mental health and emotional resilience.Click here to buy
Share Online!
