Concentration unit definition:\nThe number of gram-moles of solute dissolved per litre of solution is called…

Difficulty: Easy

Correct Answer: molarity

Explanation:


Introduction / Context:
Different analytical and process problems call for different concentration measures. Molarity is ubiquitous in laboratory work and reaction-rate expressions because it references the actual solution volume at the condition of interest.



Given Data / Assumptions:

  • Molarity (M) = moles of solute per litre of solution.
  • Other units exist (molality, normality, formality) and should not be confused with molarity.
  • Temperature can change solution volume, hence molarity can be temperature-dependent.


Concept / Approach:
Identify the unit that matches “gram-moles per litre of solution.” This maps directly to molarity. Molality uses kilograms of solvent; normality uses equivalents per litre; equivalent weight is not a concentration unit.



Step-by-Step Clarification:

Molarity M = n_solute / V_solution(L).Molality m = n_solute / mass_solvent(kg).Normality N = equivalents / litre (context-dependent on reaction).


Verification / Alternative check:
Check typical notations: 1.0 M HCl means 1 mole HCl in each litre of final solution volume, consistent with the definition.



Why Other Options Are Wrong:

  • Equivalent weight: Property of a substance, not a concentration unit.
  • Molality/Normality/Formality: Do not match the “per litre of solution” wording.


Common Pitfalls:
Interchanging molarity and molality; ignoring temperature effects on solution volume when high precision is needed.



Final Answer:
molarity

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