Acidifiers: Dilute HCl MCQs With Answer

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Acidifiers: Dilute HCl is an essential topic for B.Pharm students, covering the pharmaceutical use of dilute hydrochloric acid in formulations, pH adjustment, and dissolution testing. This introduction explains dilute HCl roles in forming hydrochloride salts, enhancing solubility of weak bases, influencing stability of acid-labile drugs, and meeting pharmacopoeial standards. It also highlights practical skills like titration, molarity/normality calculations, safe handling, storage, and lab techniques, plus regulatory requirements and illustrative case examples. Keywords such as acidifiers, dilute HCl, pH adjustment, dissolution testing, and pharmaceutical acidification are included to aid exam preparation and SEO visibility. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary function of an acidifier like dilute HCl in a pharmaceutical formulation?

  • To act as an antioxidant
  • To lower pH and improve solubility of basic drugs
  • To increase viscosity of solutions
  • To act as a chelating agent

Correct Answer: To lower pH and improve solubility of basic drugs

Q2. Which concentration of dilute HCl is commonly used as simulated gastric fluid in dissolution testing?

  • 1.0 N HCl
  • 0.01 N HCl
  • 0.1 N HCl
  • 0.5 N HCl

Correct Answer: 0.1 N HCl

Q3. How does dilute HCl enhance the solubility of a weakly basic drug?

  • By forming insoluble salts
  • By converting the base to its more water-soluble hydrochloride salt
  • By oxidizing the drug molecule
  • By removing water from the solution

Correct Answer: By converting the base to its more water-soluble hydrochloride salt

Q4. Which statement about hydrochloric acid (HCl) is correct?

  • HCl is a weak diprotic acid
  • HCl is a strong monoprotic acid that fully dissociates in water
  • HCl partially dissociates at all concentrations
  • HCl is a base at low concentrations

Correct Answer: HCl is a strong monoprotic acid that fully dissociates in water

Q5. When preparing a buffer or adjusting pH in a formulation, why might dilute HCl be used?

  • To increase ionic strength without changing pH
  • To lower pH by supplying protons and shifting ionization equilibria
  • To chelate metal ions
  • To act as a surfactant

Correct Answer: To lower pH by supplying protons and shifting ionization equilibria

Q6. Which indicator is commonly suitable for titration of dilute HCl with a strong base like NaOH?

  • Starch
  • Phenolphthalein
  • Methyl red only
  • Alizarin

Correct Answer: Phenolphthalein

Q7. What is the pH of a 0.1 N (0.1 M) solution of HCl at 25°C (ignoring activity coefficients)?

  • pH 7.0
  • pH 1.0
  • pH 3.0
  • pH 0.1

Correct Answer: pH 1.0

Q8. Which is the correct safety practice when diluting concentrated HCl?

  • Always add water to acid
  • Always add acid to water slowly with stirring
  • Heat the mixture to speed dilution
  • Mix acid and organic solvent directly

Correct Answer: Always add acid to water slowly with stirring

Q9. Which material is least suitable for long-term storage of concentrated HCl?

  • Glass bottle
  • HDPE plastic container
  • Aluminum canister
  • PTFE-lined container

Correct Answer: Aluminum canister

Q10. How many milliliters of 1 M HCl are required to prepare 500 mL of 0.1 M HCl?

  • 50 mL
  • 100 mL
  • 5 mL
  • 500 mL

Correct Answer: 50 mL

Q11. In a titration, which primary standard is commonly used to standardize dilute HCl?

  • Potassium hydrogen phthalate (KHP)
  • Sodium chloride
  • Sodium carbonate (Na2CO3)
  • Calcium carbonate

Correct Answer: Sodium carbonate (Na2CO3)

Q12. Which effect would dilute HCl have on an acid-labile drug during formulation?

  • It would stabilize the drug against hydrolysis
  • It could catalyze degradation (hydrolysis) of the drug
  • It would convert the drug to a less soluble form
  • It would chelate the drug and protect it

Correct Answer: It could catalyze degradation (hydrolysis) of the drug

Q13. Which of the following is a direct consequence of lowering gastric pH with an acidifier when dosing a weak base drug?

  • Decreased dissolution of the weak base
  • Increased ionization and often increased dissolution of the weak base
  • No change in ionization
  • Formation of a less soluble neutral species

Correct Answer: Increased ionization and often increased dissolution of the weak base

Q14. Which of these statements about normality (N) and molarity (M) for HCl is correct?

  • Normality is always twice the molarity for HCl
  • For monoprotic HCl, normality equals molarity
  • Normality is not defined for HCl
  • Molarity is always greater than normality for HCl

Correct Answer: For monoprotic HCl, normality equals molarity

Q15. Which practice is recommended for neutralizing a small lab spill of dilute HCl?

  • Neutralize with sodium bicarbonate then absorb and dispose
  • Flush directly into a metal sink
  • Add concentrated sulfuric acid to neutralize
  • Evaporate the acid under heat

Correct Answer: Neutralize with sodium bicarbonate then absorb and dispose

Q16. What happens when an amine-containing drug is treated with dilute HCl?

  • The amine is oxidized to a nitro compound
  • The amine is converted to a water-soluble hydrochloride salt
  • The drug becomes lipid-soluble and precipitates
  • The amine is transformed into an ester

Correct Answer: The amine is converted to a water-soluble hydrochloride salt

Q17. Which effect does chloride ion from dilute HCl commonly have in pharmaceutical preparations?

  • Acts as a strong oxidizing agent
  • May participate in salt formation and affect ionic strength
  • Precipitates proteins by chelation
  • Acts as a surfactant

Correct Answer: May participate in salt formation and affect ionic strength

Q18. Which drug type is most likely to show increased gastric absorption in the presence of dilute HCl?

  • Weak acids (pKa < 4)
  • Non-ionizable lipophilic drugs
  • Weak bases (higher pKa) that ionize at low pH
  • Large protein biologics

Correct Answer: Weak bases (higher pKa) that ionize at low pH

Q19. Which of the following excipients may react adversely with dilute HCl to release CO2 gas?

  • Sodium chloride
  • Sodium bicarbonate
  • Microcrystalline cellulose
  • Magnesium stearate

Correct Answer: Sodium bicarbonate

Q20. Why is it important to control the concentration of dilute HCl in dissolution media?

  • Concentration only affects osmolarity, not dissolution
  • pH influences drug ionization and dissolution rate
  • Higher HCl always prevents microbial growth only
  • It prevents oxidation of the drug

Correct Answer: pH influences drug ionization and dissolution rate

Q21. Which clinical formulation commonly uses hydrochloride salts of active drugs?

  • Free base oral suspensions only
  • Hydrochloride salts for improved water solubility and bioavailability
  • Lipidic prodrugs exclusively
  • None; HCl is not used in drug salts

Correct Answer: Hydrochloride salts for improved water solubility and bioavailability

Q22. Which measurement technique commonly involves dilute HCl as a solvent or medium in pharmaceutical analysis?

  • UV-visible spectroscopy when acid media required
  • Gas chromatography for volatile substances only
  • Mass spectrometry that requires basic media
  • Flame photometry exclusively for organic solvents

Correct Answer: UV-visible spectroscopy when acid media required

Q23. Which precaution is most important when handling dilute HCl in the laboratory?

  • Wear PPE: gloves, goggles, and lab coat
  • Store it near flammable solvents
  • Always pipette by mouth for accuracy
  • Never ventilate the area

Correct Answer: Wear PPE: gloves, goggles, and lab coat

Q24. Which drug is known to be acid-labile and may degrade in the presence of dilute HCl?

  • Penicillin G
  • Propranolol
  • Metformin
  • Ibuprofen

Correct Answer: Penicillin G

Q25. What is the major hazard pictogram for concentrated hydrochloric acid under GHS/CLP?

  • Exploding bomb
  • Corrosion (acid burns to skin/eyes)
  • Flame over circle
  • Skull and crossbones only

Correct Answer: Corrosion (acid burns to skin/eyes)

Q26. Which of the following best describes the role of dilute HCl in salt formation during drug development?

  • It oxidizes the drug to create a salt
  • It protonates basic functional groups to form hydrochloride salts
  • It esterifies drugs with chloride
  • It polymerizes small molecules

Correct Answer: It protonates basic functional groups to form hydrochloride salts

Q27. How many moles of NaOH are required to neutralize 0.2 mol of HCl?

  • 0.1 mol
  • 0.2 mol
  • 0.4 mol
  • 0.05 mol

Correct Answer: 0.2 mol

Q28. Which statement about the dissolution medium “0.1 N HCl” is TRUE?

  • It is used to simulate intestinal fluid
  • It approximates the acidic environment of the stomach
  • It is alkaline
  • It contains enzymes like pepsin by default

Correct Answer: It approximates the acidic environment of the stomach

Q29. When converting the free base of a drug to its hydrochloride salt, which process typically occurs?

  • Deprotonation of the drug
  • Protonation of the basic amine to give a chloride counterion
  • Oxidation of the amine to a nitroso derivative
  • Formation of an ester linkage

Correct Answer: Protonation of the basic amine to give a chloride counterion

Q30. Which of these procedures is essential when standardizing a NaOH solution against dilute HCl?

  • Use an appropriate primary standard and titration method
  • Assume concentration from label without testing
  • Never use an indicator
  • Heat the solution to 100°C before titration

Correct Answer: Use an appropriate primary standard and titration method

Q31. Which is the best first-aid measure for skin contact with dilute HCl?

  • Wipe off with dry cloth and leave
  • Rinse with copious water for at least 15 minutes
  • Cover with oil immediately
  • Apply baking soda paste and wrap tightly

Correct Answer: Rinse with copious water for at least 15 minutes

Q32. Which property of a drug is most directly altered when forming a hydrochloride salt?

  • Optical rotation only
  • Melting point only
  • Water solubility and dissolution behavior
  • Color only

Correct Answer: Water solubility and dissolution behavior

Q33. Which of the following best explains why dilute HCl can accelerate ester hydrolysis?

  • Acid catalysis increases the rate of ester hydrolysis by protonating the carbonyl oxygen
  • HCl acts as a base to attack the ester
  • HCl removes water from the reaction
  • HCl forms stable ester complexes that slow hydrolysis

Correct Answer: Acid catalysis increases the rate of ester hydrolysis by protonating the carbonyl oxygen

Q34. Which container labeling detail is most important for stored dilute HCl in the pharmaceutical lab?

  • Date of preparation and concentration
  • Only the supplier name
  • Color of the cap
  • Storage shelf number only

Correct Answer: Date of preparation and concentration

Q35. What is the recommended method of disposal for moderate amounts of dilute HCl after neutralization?

  • Neutralize to near pH 7 and flush to sanitary sewer if permitted
  • Pour directly into storm drains
  • Incinerate the liquid
  • Dispose as hazardous organic solvent waste

Correct Answer: Neutralize to near pH 7 and flush to sanitary sewer if permitted

Q36. Which of the following excipients is most likely to be incompatible with dilute HCl due to acid-catalyzed degradation?

  • Cellulose derivatives that are acid-stable
  • Sugar alcohols (generally stable)
  • Lactose (may undergo acid-catalyzed hydrolysis or Maillard reactions)
  • Magnesium stearate (generally stable)

Correct Answer: Lactose (may undergo acid-catalyzed hydrolysis or Maillard reactions)

Q37. A student needs 250 mL of 0.05 M HCl. How many mL of 1.0 M HCl should be measured and diluted to volume?

  • 12.5 mL
  • 125 mL
  • 25 mL
  • 2.5 mL

Correct Answer: 12.5 mL

Q38. Which analytical parameter in formulation testing can be directly affected by chloride ions from dilute HCl?

  • Viscosity only
  • Buffer capacity and ionic strength, which influence solubility and assay outcomes
  • Color exclusively
  • Lipid partitioning only

Correct Answer: Buffer capacity and ionic strength, which influence solubility and assay outcomes

Q39. Which of the following is a correct statement about using dilute HCl in quality control of tablets?

  • It is never used in QC testing
  • It can be used in dissolution tests to simulate gastric conditions
  • It must be replaced with organic solvents
  • It always denatures APIs

Correct Answer: It can be used in dissolution tests to simulate gastric conditions

Q40. Which of these is a common sign of HCl inhalation exposure in the laboratory?

  • Asymptomatic in all cases
  • Coughing, throat irritation, and difficulty breathing
  • Immediate euphoria
  • Loss of vision only

Correct Answer: Coughing, throat irritation, and difficulty breathing

Q41. Why is it important to consider activity coefficients when working with concentrated HCl solutions in calculations?

  • Because ionic strength alters effective concentration and pH
  • Activity coefficients are irrelevant for all acids
  • They only matter for nonpolar solvents
  • They increase molecular weight

Correct Answer: Because ionic strength alters effective concentration and pH

Q42. Which practice improves accuracy when preparing dilute HCl volumetrically?

  • Use uncalibrated beakers for final volume
  • Use a calibrated volumetric flask and pipette the concentrated aliquot
  • Estimate volumes by eye
  • Prepare by serial dilution without calibration

Correct Answer: Use a calibrated volumetric flask and pipette the concentrated aliquot

Q43. Which one of these is a likely storage condition to minimize HCl degradation of nearby sensitive materials?

  • Store dilute HCl next to reactive metals
  • Store dilute HCl in a ventilated, acid-compatible cabinet away from alkalis and metals
  • Store dilute HCl in direct sunlight at high temperature
  • Store dilute HCl with flammable solvents

Correct Answer: Store dilute HCl in a ventilated, acid-compatible cabinet away from alkalis and metals

Q44. Which pharmaceutical test may require adjustment of pH to an acidic range using dilute HCl?

  • Osmolarity measurement only
  • Determination of API solubility and forced degradation in acidic hydrolysis studies
  • Microbial endotoxin assay only
  • Sterility testing exclusively

Correct Answer: Determination of API solubility and forced degradation in acidic hydrolysis studies

Q45. What is the stoichiometric relationship between HCl and carbonate ion during neutralization?

  • One mole HCl reacts with two moles carbonate ion
  • Two moles HCl react with one mole carbonate ion to produce CO2, H2O, and chloride
  • HCl does not react with carbonate
  • One HCl reacts with one carbonate to produce metal salts only

Correct Answer: Two moles HCl react with one mole carbonate ion to produce CO2, H2O, and chloride

Q46. Which change in formulation performance is expected if an excipient is neutralized by dilute HCl?

  • No change in dissolution at all
  • Possible change in tablet disintegration, dissolution, and drug release profile
  • Guaranteed increased potency
  • Immediate conversion to a gaseous product

Correct Answer: Possible change in tablet disintegration, dissolution, and drug release profile

Q47. Which analytical quality attribute is directly impacted by incorrect concentration of dilute HCl in a dissolution medium?

  • Color only
  • Drug release profile and dissolution rate
  • Tablet hardness only
  • Ambient humidity

Correct Answer: Drug release profile and dissolution rate

Q48. Which PPE is least important when handling dilute HCl compared to the others?

  • Chemical-resistant gloves
  • Safety goggles
  • Lab coat
  • Flame-retardant apron (for dilute acid only)

Correct Answer: Flame-retardant apron (for dilute acid only)

Q49. Which of these actions should you avoid when a bottle of concentrated HCl is found leaking in the lab?

  • Evacuate and ventilate the area and alert trained personnel
  • Neutralize small controlled spills only if trained and equipped
  • Contain the spill with reactive metals to absorb acid
  • Don appropriate PPE before attempting any cleanup

Correct Answer: Contain the spill with reactive metals to absorb acid

Q50. Which is a correct summary of why dilute HCl is important in pharmaceutical education for B.Pharm students?

  • It is only relevant to organic chemistry and not formulations
  • It plays a key role in pH control, dissolution testing, salt formation, stability studies, and safe laboratory practice
  • It is obsolete and not used in modern pharmaceutics
  • It has no effect on drug solubility or formulation

Correct Answer: It plays a key role in pH control, dissolution testing, salt formation, stability studies, and safe laboratory practice

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