Methods of expressing concentration MCQs With Answer

Methods of expressing concentration MCQs With Answer

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Understanding methods of expressing concentration is essential for B. Pharm students performing pharmaceutical calculations, compounding, formulation, and analytical assays. This topic covers molarity, molality, normality, mole fraction, mass percent, percent w/v and v/v, parts per million (ppm), and equivalents — explaining when and why each unit is used, how to convert between units, and common pitfalls in dilution and titration problems. Emphasis on practical examples, units, and significant figures helps ensure accuracy in dosage calculations, stability studies, and quality control. Mastery of these concepts supports safe formulation and precise assay interpretation in pharmacy practice. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which definition correctly describes molarity?

  • Moles of solute per kilogram of solvent
  • Moles of solute per liter of solution
  • Grams of solute per 100 mL of solution
  • Moles of solute per liter of solvent

Correct Answer: Moles of solute per liter of solution

Q2. Molality is most useful compared to molarity because it is independent of which variable?

  • Temperature
  • Pressure
  • Volume changes with temperature
  • Concentration gradient

Correct Answer: Volume changes with temperature

Q3. Normality (N) expresses concentration based on:

  • Moles of solute per liter of solution
  • Moles of solute per kilogram of solvent
  • Equivalents of reactive species per liter of solution
  • Mass fraction of solute in solution

Correct Answer: Equivalents of reactive species per liter of solution

Q4. How many grams of NaCl (MW = 58.44 g/mol) are required to prepare 1 L of 0.9% w/v NaCl?

  • 0.9 g
  • 9 g
  • 90 g
  • 900 g

Correct Answer: 9 g

Q5. Percent w/v is defined as:

  • Grams of solute per 100 grams of solution
  • Milligrams of solute per liter of solution
  • Grams of solute per 100 mL of solution
  • Volume of solute per 100 mL of solution

Correct Answer: Grams of solute per 100 mL of solution

Q6. Which concentration expression is dimensionless?

  • Molarity
  • Mole fraction
  • Molality
  • Normality

Correct Answer: Mole fraction

Q7. Parts per million (ppm) commonly equals:

  • mg per L for dilute aqueous solutions
  • g per 100 mL
  • Moles per kilogram
  • Equivalents per liter

Correct Answer: mg per L for dilute aqueous solutions

Q8. To convert molarity to molality one must know:

  • The molecular weight of solvent only
  • The density of the solution
  • The percent purity of solute only
  • The boiling point elevation constant

Correct Answer: The density of the solution

Q9. A 1 M solution of H2SO4 contains how many equivalents per liter for acid–base reactions?

  • 0.5 equivalents per liter
  • 1 equivalent per liter
  • 2 equivalents per liter
  • Depends on titrant concentration

Correct Answer: 2 equivalents per liter

Q10. Which method expresses concentration as mass of solute divided by mass of solution multiplied by 100?

  • Percent w/v
  • Percent v/v
  • Mass percent (w/w)
  • Molarity

Correct Answer: Mass percent (w/w)

Q11. If a solution has a mole fraction of ethanol of 0.2, the mole fraction of water is:

  • 0.8
  • 0.2
  • 1.2
  • Cannot be determined

Correct Answer: 0.8

Q12. Which concentration unit is most appropriate for expressing ionic strength and osmotic effects?

  • Molality
  • Mole fraction
  • Osmolarity (osmol per liter)
  • Percent v/v

Correct Answer: Osmolarity (osmol per liter)

Q13. A 5% v/v ethanol solution means:

  • 5 mL ethanol in 100 mL solution
  • 5 g ethanol in 100 g solution
  • 5 mol ethanol in 100 L solution
  • 5 mL ethanol per liter

Correct Answer: 5 mL ethanol in 100 mL solution

Q14. Which statement about molarity and temperature is true?

  • Molarity is independent of temperature
  • Molarity varies with temperature due to volume change
  • Molarity equals molality at all temperatures
  • Molarity depends only on mass of solute

Correct Answer: Molarity varies with temperature due to volume change

Q15. In a titration, the normality of an acid solution is 0.1 N. For monoprotic acid, its molarity is:

  • 0.05 M
  • 0.1 M
  • 0.2 M
  • Cannot determine

Correct Answer: 0.1 M

Q16. Which conversion is correct for a strong electrolyte that dissociates completely: 1 osmole of NaCl equals:

  • 1 mole of particles in solution
  • 2 osmoles of particles in solution
  • 0.5 osmole of particles
  • Depends on ionic strength only

Correct Answer: 2 osmoles of particles in solution

Q17. What is the main drawback of using percent v/v for concentrated mixtures?

  • It is temperature-independent
  • Volumes are strictly additive for all mixtures
  • Volumes may not be additive due to contraction or expansion
  • It requires molar mass

Correct Answer: Volumes may not be additive due to contraction or expansion

Q18. A stock solution is 2 M. To prepare 500 mL of 0.5 M from it, the required volume of stock is:

  • 125 mL
  • 250 mL
  • 50 mL
  • 1000 mL

Correct Answer: 125 mL

Q19. Which concentration expression would you choose to report composition in vapor–liquid equilibrium calculations?

  • Molality
  • Mole fraction
  • Percent w/v
  • Normality

Correct Answer: Mole fraction

Q20. For very dilute aqueous solutions, 1 ppm roughly equals:

  • 1 mg/L
  • 1 g/L
  • 1 μg/L
  • 1 mol/L

Correct Answer: 1 mg/L

Q21. Equivalent weight for an acid is defined as:

  • Molecular weight divided by number of moles
  • Molecular weight divided by valence (number of replaceable H+)
  • Molecular weight multiplied by valence
  • Mass of solvent per mole of solute

Correct Answer: Molecular weight divided by valence (number of replaceable H+)

Q22. A solution containing 10 g of solute in 200 g of solution has what percent w/w?

  • 2%
  • 5%
  • 20%
  • 50%

Correct Answer: 5%

Q23. Which concentration unit is most appropriate for reporting gravimetric assay results of an active pharmaceutical ingredient in tablet powder?

  • Molarity
  • Percent w/w
  • Normality
  • Osmolarity

Correct Answer: Percent w/w

Q24. When converting between molarity and normality for polyprotic acids, you must consider:

  • Only the molecular weight
  • The number of reactive equivalents per molecule
  • Density of pure acid only
  • Temperature of reaction

Correct Answer: The number of reactive equivalents per molecule

Q25. Which expression gives the concentration in terms of mass of solute per total volume of solution?

  • Percent w/v
  • Mole fraction
  • Molality
  • Normality

Correct Answer: Percent w/v

Q26. A pharmacist prepares 250 mL of 0.2 M glucose (MW 180 g/mol). The mass of glucose required is closest to:

  • 9.0 g
  • 36.0 g
  • 0.9 g
  • 180 g

Correct Answer: 9.0 g

Q27. In solution chemistry, colligative properties depend primarily on:

  • Nature of solute particles
  • Type of solvent only
  • Number of solute particles per unit solvent
  • Color of solution

Correct Answer: Number of solute particles per unit solvent

Q28. Which concentration unit would be most convenient when preparing intravenous electrolyte solutions where osmotic effect matters?

  • Molarity
  • Normality
  • Osmolarity
  • Mole fraction

Correct Answer: Osmolarity

Q29. For a solution containing 0.1 mol solute in 1 kg solvent, the concentration is:

  • 0.1 M
  • 0.1 m (molal)
  • 0.1 N
  • 0.1 mole fraction

Correct Answer: 0.1 m (molal)

Q30. When expressing concentration for quality control limits of trace impurities, which units are commonly used?

  • Percent w/v only
  • Molality and normality
  • ppm or ppb
  • Molarity and mole fraction

Correct Answer: ppm or ppb

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