Structure and uses of oxalic acid MCQs With Answer is a focused study guide designed for B. Pharm students to master the chemistry, properties, and pharmaceutical relevance of oxalic acid. This introduction covers molecular structure (ethanedioic acid), acid strength, oxalate coordination behavior, physical and chemical properties, synthesis routes, analytical applications, toxicology and practical uses such as metal cleaning, bleaching and standardization in redox titrations. These SEO-friendly MCQs emphasize exam-relevant facts, mechanisms and safety considerations to strengthen conceptual understanding and application in pharmaceutics. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the correct molecular formula of oxalic acid?
- H2C2O4
- H2C2O3
- H2C3O4
- H4C2O4
Correct Answer: H2C2O4
Q2. What is the IUPAC name of oxalic acid?
- Ethane-1,2-diol
- Ethanoic acid
- Ethandioic acid
- Oxalyl chloride
Correct Answer: Ethandioic acid
Q3. How many carboxylic acid groups are present in one molecule of oxalic acid?
- One
- Two
- Three
- None
Correct Answer: Two
Q4. Which structural formula correctly represents oxalic acid?
- HO–CH2–CH2–OH
- HOOC–COOH
- CH3COOH
- HO–C≡C–OH
Correct Answer: HOOC–COOH
Q5. Oxalic acid is classified as which type of organic acid?
- Monocarboxylic acid
- Dicarboxylic acid
- Tricarboxylic acid
- Hydroxy acid
Correct Answer: Dicarboxylic acid
Q6. Which statement about oxalic acid acidity is correct?
- It is a weaker acid than acetic acid
- It has two dissociable protons with different pKa values
- It is a non-dissociable acid in water
- Both protons dissociate simultaneously at the same pKa
Correct Answer: It has two dissociable protons with different pKa values
Q7. Which of the following best describes the oxalate ion?
- Monovalent anion CO2−
- Bidentate dianion C2O4(2−)
- Neutral molecule C2O4
- Radical species C2O4•
Correct Answer: Bidentate dianion C2O4(2−)
Q8. Oxalic acid commonly occurs in nature in which form in plants?
- As free oxalic acid gas
- As insoluble calcium oxalate crystals
- As oxalic acid esters only
- As elemental carbon deposits
Correct Answer: As insoluble calcium oxalate crystals
Q9. Which of the following is a common laboratory method to detect oxalate in urine or plant tissues?
- Test for chloride ions
- Microscopic identification of calcium oxalate crystals
- Measurement of ammonia evolution
- Color change with Benedict’s reagent
Correct Answer: Microscopic identification of calcium oxalate crystals
Q10. Which property makes oxalate a good chelating ligand for metal ions?
- Its long aliphatic chain
- Its ability to act as a bidentate ligand forming five-membered chelate rings
- Its aromatic stability
- Its monodentate binding through carbon
Correct Answer: Its ability to act as a bidentate ligand forming five-membered chelate rings
Q11. Which salt of oxalic acid is commonly used as a primary standard to standardize potassium permanganate?
- Calcium oxalate
- Sodium oxalate
- Magnesium oxalate
- Oxalic acid dihydrate
Correct Answer: Sodium oxalate
Q12. Which reagent is commonly reduced by oxalic acid in redox titrations?
- Hydrochloric acid
- Potassium permanganate (KMnO4)
- Sodium hydroxide
- Silver nitrate
Correct Answer: Potassium permanganate (KMnO4)
Q13. What is a key industrial use of oxalic acid?
- As a fuel additive
- As a metal cleaning and rust removal agent
- As a polymerization initiator for plastics
- As an oil lubricant
Correct Answer: As a metal cleaning and rust removal agent
Q14. Oxalic acid is commonly available in which solid form?
- Anhydrous only
- Dihydrate crystalline form
- Gaseous form
- Polymeric resin
Correct Answer: Dihydrate crystalline form
Q15. Which of the following hazards is most associated with oxalic acid exposure?
- Nephrotoxicity and kidney stone formation due to calcium oxalate
- Immediate cardiac arrest by contact
- Highly flammable vapor explosion
- Radioactive contamination
Correct Answer: Nephrotoxicity and kidney stone formation due to calcium oxalate
Q16. Which statement about solubility of oxalic acid dihydrate is true?
- It is insoluble in water
- It is highly soluble in water and less soluble in alcohol
- It dissolves only in nonpolar solvents
- It reacts violently with water forming a gas
Correct Answer: It is highly soluble in water and less soluble in alcohol
Q17. In coordination chemistry, oxalate can act as which types of ligand?
- Only monodentate
- Monodentate and tridentate
- Bidentate and bridging ligand
- Only tetradentate
Correct Answer: Bidentate and bridging ligand
Q18. Which of the following reactions involves oxalic acid as a reagent in organic synthesis?
- Formation of oxalyl chloride used for acylation
- Direct nitration of benzene
- Polymerization of ethylene
- Hydrogenation of alkenes
Correct Answer: Formation of oxalyl chloride used for acylation
Q19. Oxalic acid can be prepared in the laboratory by oxidation of which substance?
- Ethane by catalytic hydrogenation
- Carbohydrates such as sucrose by strong oxidizers
- Alkanes by photolysis
- Elemental sulfur by combustion
Correct Answer: Carbohydrates such as sucrose by strong oxidizers
Q20. Which analytical technique is often used to quantify oxalate concentration in solutions?
- Gravimetric precipitation of chloride
- Redox titration with potassium permanganate after acid treatment
- NMR of free protons only
- Infrared spectroscopy of alkanes
Correct Answer: Redox titration with potassium permanganate after acid treatment
Q21. Which pH behavior is expected when oxalic acid is dissolved in water?
- Solution becomes strongly basic
- Solution becomes acidic due to proton release
- Solution remains neutral
- Solution emits chlorine gas
Correct Answer: Solution becomes acidic due to proton release
Q22. Which of these best describes resonance in the oxalate ion?
- Negative charge localized only on one oxygen
- Delocalization of negative charge over oxygen atoms and C–O bonds
- No resonance due to saturated carbon atoms
- Resonance only in the presence of metal ions
Correct Answer: Delocalization of negative charge over oxygen atoms and C–O bonds
Q23. Oxalate complexes with calcium are important because they are:
- Highly soluble and nontoxic
- Insoluble and can precipitate as kidney stones
- Radioactive markers
- Volatile liquids at room temperature
Correct Answer: Insoluble and can precipitate as kidney stones
Q24. Which of the following is NOT a common use of oxalic acid in pharmacy or industry?
- Metal cleaning and rust removal
- Bleaching of wood and textiles
- Primary fuel additive in gasoline
- Reducing agent in analytical chemistry
Correct Answer: Primary fuel additive in gasoline
Q25. Which analytical property makes oxalic acid useful for standardizing KMnO4 solutions?
- It forms a colored complex with KMnO4
- It undergoes a predictable redox reaction with a known stoichiometry
- It precipitates KMnO4 quantitatively
- It is a base that neutralizes KMnO4
Correct Answer: It undergoes a predictable redox reaction with a known stoichiometry
Q26. What happens to oxalic acid on heating to decomposition?
- It polymerizes to a solid resin
- It decomposes to carbon monoxide and carbon dioxide
- It sublimes unchanged as oxalic acid vapor
- It converts to acetic acid
Correct Answer: It decomposes to carbon monoxide and carbon dioxide
Q27. Which statement about oxalic acid’s role in pharmaceutical formulations is accurate?
- It is commonly used as an active pharmaceutical ingredient in tablets
- It is mainly used as a cleaning, bleaching and analytical reagent rather than as an excipient
- It is routinely used as a preservative in parenteral drugs
- It is an approved oral supplement for calcium absorption
Correct Answer: It is mainly used as a cleaning, bleaching and analytical reagent rather than as an excipient
Q28. In coordination complexes, an oxalate ligand that binds through both oxygens to one metal center is described as:
- Monodentate
- Bidentate chelating
- Protic
- Ambidentate
Correct Answer: Bidentate chelating
Q29. Which of the following methods is a green route mentioned for oxalic acid production in modern chemistry?
- Electrochemical oxidation of biomass-derived compounds
- Combustion of plastics
- Chlorination of benzene
- Direct distillation of crude oil
Correct Answer: Electrochemical oxidation of biomass-derived compounds
Q30. Which of the following best explains why oxalic acid is stronger than acetic acid?
- Oxalic acid is aromatic
- Negative charge is stabilized by resonance and electron-withdrawing adjacent carboxyl group
- Oxalic acid has a longer alkyl chain
- It forms hydrogen gas on ionization
Correct Answer: Negative charge is stabilized by resonance and electron-withdrawing adjacent carboxyl group
Q31. Which salt forms when oxalic acid reacts with sodium hydroxide in stoichiometric amounts?
- Sodium acetate
- Sodium oxalate
- Sodium carbonate
- Calcium oxalate
Correct Answer: Sodium oxalate
Q32. Which spectral technique is most useful to identify the C=O stretch of oxalic acid?
- UV-Visible spectroscopy
- Infrared (IR) spectroscopy
- Mass spectrometry for only the molecular ion
- Polarimetry
Correct Answer: Infrared (IR) spectroscopy
Q33. In a pharmaceutical lab, why must oxalic acid waste be disposed carefully?
- It is highly flammable
- It can chelate metals and cause environmental toxicity and harm organisms
- It forms harmless water on dilution
- It converts to harmless sugar on standing
Correct Answer: It can chelate metals and cause environmental toxicity and harm organisms
Q34. Which crystalline hydrate of oxalic acid is commonly encountered?
- Monohydrate
- Dihydrate
- Tetrahydrate
- Anhydrate only
Correct Answer: Dihydrate
Q35. Which of the following is a typical melting point characteristic of oxalic acid dihydrate?
- Makes ice at 0 °C
- Decomposes before a simple melt, with decomposition around 189–191 °C for the dihydrate
- Has a melting point below 0 °C
- Vaporizes at 20 °C
Correct Answer: Decomposes before a simple melt, with decomposition around 189–191 °C for the dihydrate
Q36. Which metabolite or clinical problem is directly linked to high dietary oxalate?
- Hypoglycemia
- Calcium oxalate kidney stones
- Hypercholesterolemia
- Hypertension
Correct Answer: Calcium oxalate kidney stones
Q37. Which metal commonly forms an insoluble oxalate used as an analytical precipitate?
- Sodium
- Calcium
- Potassium
- Ammonium
Correct Answer: Calcium
Q38. Which laboratory reagent is used to liberate oxalic acid from its salts for titration with KMnO4?
- Sodium hydroxide
- Sulfuric acid
- Sodium chloride
- Ammonia
Correct Answer: Sulfuric acid
Q39. Oxalyl chloride, derived from oxalic acid, is primarily used for what purpose in organic synthesis?
- As a strong base
- To convert carboxylic acids to acyl chlorides
- As a free radical initiator
- As a polymer crosslinker
Correct Answer: To convert carboxylic acids to acyl chlorides
Q40. Which of the following best describes the odor and appearance of pure oxalic acid dihydrate?
- Colorless crystals with a faint acidic odor
- Dark oily liquid with sulfur smell
- Bright yellow powder with ammonia smell
- Gaseous pungent vapor at room temperature
Correct Answer: Colorless crystals with a faint acidic odor
Q41. Which of the following biochemical roles does oxalate play in living organisms?
- Essential vitamin for metabolism
- Byproduct of metabolism and a chelator contributing to mineral crystallization
- Main source of cellular energy
- Primary oxygen carrier like hemoglobin
Correct Answer: Byproduct of metabolism and a chelator contributing to mineral crystallization
Q42. Which reagent will effectively precipitate oxalate as an insoluble salt for gravimetric analysis?
- Silver nitrate to form silver oxalate
- Calcium chloride to form calcium oxalate
- Sodium sulfate to form sodium oxalate
- Potassium permanganate to form KMnO4 precipitate
Correct Answer: Calcium chloride to form calcium oxalate
Q43. Oxalic acid acts as which of the following in redox chemistry?
- Oxidizing agent only
- Reducing agent that can reduce Mn(VII) to Mn(II)
- Inert spectator ion
- Strong radical initiator releasing chlorine
Correct Answer: Reducing agent that can reduce Mn(VII) to Mn(II)
Q44. Which safety measure is most important when handling oxalic acid in the lab?
- Use of protective gloves and eye protection to avoid skin and eye contact
- Storing in open containers at bench top
- Eating and drinking nearby is safe
- Wearing no protection because it is harmless
Correct Answer: Use of protective gloves and eye protection to avoid skin and eye contact
Q45. Which of the following is a diagnostic use of oxalate chemistry in pharmacy or clinical labs?
- Measuring blood cholesterol directly
- Standardizing KMnO4 to assess oxidizable substances in clinical samples
- Directly measuring insulin concentration
- Determining DNA sequence
Correct Answer: Standardizing KMnO4 to assess oxidizable substances in clinical samples
Q46. In a coordination compound, oxalate bridging two metal centers is described as:
- Monodentate bridging
- Bidentate bridging (μ-oxalato)
- Non-coordinated counterion
- Inner-sphere water ligand
Correct Answer: Bidentate bridging (μ-oxalato)
Q47. Which of the following statements about oxalic acid toxicity is correct?
- Ingestion of large amounts can lead to hypocalcemia and renal failure
- It is completely safe and non-toxic at any dose
- It causes immediate paralysis on skin contact
- It acts as a nutrient supplement for bones
Correct Answer: Ingestion of large amounts can lead to hypocalcemia and renal failure
Q48. Which reagent can be used to convert oxalic acid to carbon monoxide in organic transformations?
- Heating alone at low temperature
- Thermal decomposition or decomposition of oxalyl derivatives under controlled conditions
- Treatment with sodium chloride
- Reaction with nitrogen gas at room temperature
Correct Answer: Thermal decomposition or decomposition of oxalyl derivatives under controlled conditions
Q49. Which of the following best describes why oxalate forms insoluble salts with calcium?
- Because oxalate is positively charged
- Because calcium oxalate has very low aqueous solubility due to lattice energy
- Because calcium converts oxalate to gas
- Because oxalate is volatile
Correct Answer: Because calcium oxalate has very low aqueous solubility due to lattice energy
Q50. For B.Pharm students, why is understanding oxalic acid important?
- Only for culinary uses of oxalate-rich foods
- Because oxalic acid chemistry impacts pharmaceutical analysis, safety, metal cleaning, and clinical implications like kidney stones
- It has no relevance to pharmacy education
- Because it is a primary therapeutic agent in most drugs
Correct Answer: Because oxalic acid chemistry impacts pharmaceutical analysis, safety, metal cleaning, and clinical implications like kidney stones
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