Theory of titration of strong acids and bases MCQs With Answer

Theory of titration of strong acids and bases MCQs With Answer

Theory of titration of strong acids and bases is essential for B.Pharm students learning volumetric analysis, neutralization, pH curves, equivalence point and indicator selection. This concise introduction covers titration principles, titrant and titrate behaviour, calculation using MaVa = MbVb, the characteristic steep titration curve, and why the equivalence pH is ~7 at 25°C. Topics include initial and post-equivalence pH, choice of indicators (phenolphthalein, methyl orange), and practical issues like endpoint detection with indicators or pH meters. Understanding these fundamentals supports pharmaceutical assay, drug formulation and quality control. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary principle behind titration of a strong acid with a strong base?

• Gradual mixing until the titrant color changes regardless of reaction
• Neutralization reaction between known concentration titrant and unknown concentration analyte
• Formation of a precipitate to indicate endpoint
• Measuring conductivity changes only

Correct Answer: Neutralization reaction between known concentration titrant and unknown concentration analyte

Q2. At 25°C, what is the expected pH at the equivalence point when titrating a strong acid with a strong base?

• pH < 7
• pH = 7
• pH > 7
• pH depends on indicator used

Correct Answer: pH = 7

Q3. Which indicator is most commonly preferred for strong acid–strong base titrations due to its endpoint in the alkaline range?

• Methyl orange
• Bromothymol blue
• Phenolphthalein
• Litmus

Correct Answer: Phenolphthalein

Q4. How does the titration curve of a strong acid vs strong base typically appear around the equivalence point?

• Gradual slope with no steep region
• Steep, almost vertical rise in pH near equivalence
• Multiple small jumps in pH
• Flat line at pH 7 throughout

Correct Answer: Steep, almost vertical rise in pH near equivalence

Q5. For a 0.01 M strong acid, what is the initial pH before any titrant is added?

• 0.01
• 2
• 7
• 12

Correct Answer: 2

Q6. Which equation directly relates volumes and molarities at equivalence for monoprotic acids and bases?

• pH = -log[H+]
• Ma × Va = Mb × Vb
• Kw = [H+][OH-]
• Ka × Kb = Kw

Correct Answer: Ma × Va = Mb × Vb

Q7. Why is the equivalence pH exactly neutral (≈7) for strong acid–strong base titrations at 25°C?

• Because indicators force the pH to 7
• Because the resulting salt hydrolyzes strongly
• Because H+ and OH- completely neutralize leaving pure water with Kw dependent pH
• Because titration volumes are equal

Correct Answer: Because H+ and OH- completely neutralize leaving pure water with Kw dependent pH

Q8. Which statement about the half-neutralization point in a strong acid–strong base titration is correct?

• The half-neutralization point yields pH = pKa
• The half-neutralization point forms a significant buffer
• There is no meaningful buffer region; pH is not related to pKa
• It always equals pH 7

Correct Answer: There is no meaningful buffer region; pH is not related to pKa

Q9. If 25.0 mL of 0.10 M HCl is titrated with 0.10 M NaOH, what volume of NaOH is required to reach equivalence?

• 12.5 mL
• 25.0 mL
• 50.0 mL
• 100.0 mL

Correct Answer: 25.0 mL

Q10. Which parameter primarily determines the steepness of the pH change near equivalence in strong acid–strong base titrations?

• Concentration of analyte and titrant
• Color of the indicator
• Shape of the burette
• Ambient light

Correct Answer: Concentration of analyte and titrant

Q11. What is the predominant species in solution immediately after the equivalence point when NaOH is added to HCl?

• Excess HCl
• Excess NaOH
• NaCl and water, with excess OH- if past equivalence
• The undissociated acid

Correct Answer: NaCl and water, with excess OH- if past equivalence

Q12. Which instrument provides a more precise endpoint detection than visual indicators during titration?

• Analytical balance
• pH meter
• Thermometer
• Conductivity meter (not calibrated)

Correct Answer: pH meter

Q13. For strong base initial pH calculation, which formula is appropriate given [OH-]?

• pH = -log[H+]
• pOH = -log[OH-], then pH = 14 – pOH
• pH = -log[OH-]
• pH = Ka × [base]

Correct Answer: pOH = -log[OH-], then pH = 14 – pOH

Q14. Which indicator range is closest to phenolphthalein’s transition useful for strong acid–strong base titrations?

• pH 3.1 – 4.4
• pH 6.0 – 7.6
• pH 8.2 – 10.0
• pH 1.0 – 2.0

Correct Answer: pH 8.2 – 10.0

Q15. In pharmaceutical assays, why is volumetric titration of strong acid–strong base still widely used?

• It requires expensive instrumentation only
• It provides simple, accurate assay of active ingredients via neutralization
• It avoids any sample preparation
• It is insensitive to concentration changes

Correct Answer: It provides simple, accurate assay of active ingredients via neutralization

Q16. When titrating 50.0 mL of 0.200 M NaOH with 0.100 M HCl, what volume of HCl is required for equivalence?

• 25.0 mL
• 50.0 mL
• 100.0 mL
• 200.0 mL

Correct Answer: 100.0 mL

Q17. Which of these salts formed by neutralization of a strong acid and strong base will hydrolyze significantly in water?

• NaCl
• KNO3
• NH4Cl
• All are neutral and do not hydrolyze significantly

Correct Answer: All are neutral and do not hydrolyze significantly

Q18. Which factor can cause an apparent endpoint error if not controlled during titration?

• Slow titrant addition near the end point
• Using a correct molarity titrant
• Calibration of pH meter
• Precise burette readings

Correct Answer: Slow titrant addition near the end point

Q19. Which statement best describes the buffer region in strong acid–strong base titrations?

• A broad buffer region exists due to weak acid formation
• No significant buffer region is present because both species fully dissociate
• Buffer region equals the equivalence region
• Buffer forms only with methyl orange

Correct Answer: No significant buffer region is present because both species fully dissociate

Q20. What is the effect of increasing both titrant and analyte concentrations proportionally on the titration curve?

• The equivalence point pH shifts dramatically
• The steepness around equivalence increases, making endpoint detection sharper
• The titration becomes impossible
• The equivalence volume changes unpredictably

Correct Answer: The steepness around equivalence increases, making endpoint detection sharper

Q21. When selecting an indicator for a given titration, what is the most important criterion?

• Indicator price
• Indicator pH transition range should overlap the titration curve’s steep region near equivalence
• Indicator color should be red
• Indicator must be weak

Correct Answer: Indicator pH transition range should overlap the titration curve’s steep region near equivalence

Q22. For strong acid–strong base titration, what is the effect of temperature on the equivalence point pH?

• No effect; always pH 7 at any temperature
• Equivalence pH can vary slightly because Kw changes with temperature
• Equivalence pH becomes extremely acidic at high temperatures
• Temperature only affects indicator color, not pH

Correct Answer: Equivalence pH can vary slightly because Kw changes with temperature

Q23. What is the best choice of indicator to detect the endpoint when titrating a strong base with a strong acid?

• Phenolphthalein (turns color in alkaline range)
• Methyl orange (turns color in acidic range)
• Any indicator works equally well
• Indicator selection is not necessary if volumes are measured

Correct Answer: Methyl orange (turns color in acidic range)

Q24. During titration, why are smaller additions of titrant recommended when approaching the endpoint?

• To save titrant
• Because pH changes are smallest and unimportant
• To avoid overshooting the equivalence point due to the steep pH change
• To reduce the effect of temperature

Correct Answer: To avoid overshooting the equivalence point due to the steep pH change

Q25. Which expression correctly gives the relationship of Kw, Ka and Kb?

• Ka × Kb = Kw
• Ka + Kb = Kw
• Ka / Kb = Kw
• Ka – Kb = Kw

Correct Answer: Ka × Kb = Kw

Q26. Which statement is true about the endpoint detected by a visual indicator?

• Endpoint always exactly equals the equivalence point
• Endpoint approximates the equivalence point; choice of indicator affects closeness
• Visual endpoints are more accurate than pH meters
• Endpoint is unrelated to pH changes

Correct Answer: Endpoint approximates the equivalence point; choice of indicator affects closeness

Q27. In a titration curve of 0.1 M HCl with 0.1 M NaOH, what is the pH just before adding any NaOH?

• 0.0
• 1.0
• 7.0
• 14.0

Correct Answer: 1.0

Q28. Which salt resulting from strong acid–strong base neutralization is expected to be neutral in aqueous solution?

• NH4Cl
• NaCl
• NaF
• CH3COONa

Correct Answer: NaCl

Q29. Which practical technique improves precision when reading burette volumes during titration?

• Reading from different angles each time
• Ensuring meniscus is read at eye level and using consistent technique
• Vigorously shaking the burette before use
• Using a colored titrant regardless of chemistry

Correct Answer: Ensuring meniscus is read at eye level and using consistent technique

Q30. Which statement correctly distinguishes strong acid–strong base titration from weak acid titration?

• Only weak acid titrations have a steep equivalence steepness
• Strong acid–strong base titrations show a sharp, steep pH change at equivalence and equivalence pH near neutrality, while weak acid titrations show buffer regions and equivalence pH ≠ 7
• Weak acid titrations never require indicators
• Strong acid titrations always produce basic salts

Correct Answer: Strong acid–strong base titrations show a sharp, steep pH change at equivalence and equivalence pH near neutrality, while weak acid titrations show buffer regions and equivalence pH ≠ 7

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com